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  • 1. Acke, B.
    et al.
    Min, M.
    Dominik, C.
    Vandenbussche, B.
    Sibthorpe, B.
    Waelkens, C.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Degroote, P.
    Smolders, K.
    Pantin, E.
    Barlow, M. J.
    Blommaert, J. A. D. L.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    De Meester, W.
    Dent, W. R. F.
    Exter, K.
    Di Francesco, J.
    Fridlund, M.
    Gear, W. K.
    Glauser, A. M.
    Greaves, J. S.
    Harvey, P. M.
    Henning, Th
    Hogerheijde, M. R.
    Holland, W. S.
    Huygen, R.
    Ivison, R. J.
    Jean, C.
    Liseau, R.
    Naylor, D. A.
    Pilbratt, G. L.
    Polehampton, E. T.
    Regibo, S.
    Royer, P.
    Sicilia-Aguilar, A.
    Swinyard, B. M.
    Herschel images of Fomalhaut An extrasolar Kuiper belt at the height of its dynamical activity2012Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 540, s. A125-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Fomalhaut is a young (2 +/- 1 x 10(8) years), nearby (7.7 pc), 2 M-circle dot star that is suspected to harbor an infant planetary system, interspersed with one or more belts of dusty debris. Aims. We present far-infrared images obtained with the Herschel Space Observatory with an angular resolution between 5.7 '' and 36.7 '' at wavelengths between 70 mu m and 500 mu m. The images show the main debris belt in great detail. Even at high spatial resolution, the belt appears smooth. The region in between the belt and the central star is not devoid of material; thermal emission is observed here as well. Also at the location of the star, excess emission is detected. We aim to construct a consistent image of the Fomalhaut system. Methods. We use a dynamical model together with radiative-transfer tools to derive the parameters of the debris disk. We include detailed models of the interaction of the dust grains with radiation, for both the radiation pressure and the temperature determination. Comparing these models to the spatially resolved temperature information contained in the images allows us to place strong constraints on the presence of grains that will be blown out of the system by radiation pressure. We use this to derive the dynamical parameters of the system. Results. The appearance of the belt points toward a remarkably active system in which dust grains are produced at a very high rate by a collisional cascade in a narrow region filled with dynamically excited planetesimals. Dust particles with sizes below the blow-out size are abundantly present. The equivalent of 2000 one-km-sized comets are destroyed every day, out of a cometary reservoir amounting to 110 Earth masses. From comparison of their scattering and thermal properties, we find evidence that the dust grains are fluffy aggregates, which indicates a cometary origin. The excess emission at the location of the star may be produced by hot dust with a range of temperatures, but may also be due to gaseous free-free emission from a stellar wind.

  • 2. Amiaux, J
    et al.
    Andra, 40
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Development approach and first infrared test results of JWST/Mid Infra Red Imager Optical Bench2008Ingår i: Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter, 2008Konferensbidrag (Övrigt vetenskapligt)
  • 3. Barlow, M. J.
    et al.
    Krause, O.
    Swinyard, B. M.
    Sibthorpe, B.
    Besel, M. -A
    Wesson, R.
    Ivison, R. J.
    Dunne, L.
    Gear, W. K.
    Gomez, H. L.
    Hargrave, P. C.
    Henning, Th.
    Leeks, S. J.
    Lim, T. L.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Polehampton, E. T.
    A Herschel PACS and SPIRE study of the dust content of the Cassiopeia A supernova remnant2010Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, s. L138-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using the 3.5-m Herschel Space Observatory, imaging photometry of Cas A has been obtained in six bands between 70 and 500 mu m with the PACS and SPIRE instruments, with angular resolutions ranging from 6 to 37 ''. In the outer regions of the remnant the 70-mu m PACS image resembles the 24-mu m image Spitzer image, with the emission attributed to the same warm dust component, located in the reverse shock region. At longer wavelengths, the three SPIRE bands are increasingly dominated by emission from cold interstellar dust knots and filaments, particularly across the central, western and southern parts of the remnant. Nonthermal emission from the northern part of the remnant becomes prominent at 500 mu m. We have estimated and subtracted the contributions from the nonthermal, warm dust and cold interstellar dust components. We confirm and resolve for the first time a cool (similar to 35 K) dust component, emitting at 70-160 mu m, that is located interior to the reverse shock region, with an estimated mass of 0.075 M-circle dot.

  • 4. Barlow, M. J.
    et al.
    Swinyard, B. M.
    Owen, P. J.
    Cernicharo, J.
    Gomez, H. L.
    Ivison, R. J.
    Krause, O.
    Lim, T. L.
    Matsuura, M.
    Miller, S.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Polehampton, E. T.
    Detection of a Noble Gas Molecular Ion, (ArH+)-Ar-36, in the Crab Nebula2013Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 342, nr 6164, s. 1343-1345Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Noble gas molecules have not hitherto been detected in space. From spectra obtained with the Herschel Space Observatory, we report the detection of emission in the 617.5- and 1234.6-gigahertz J = 1-0 and 2-1 rotational lines of (ArH+)-Ar-36 at several positions in the Crab Nebula, a supernova remnant known to contain both molecular hydrogen and regions of enhanced ionized argon emission. Argon-36 is believed to have originated from explosive nucleosynthesis in massive stars during core-collapse supernova events. Its detection in the Crab Nebula, the product of such a supernova event, confirms this expectation. The likely excitation mechanism for the observed (ArH+)-Ar-36 emission lines is electron collisions in partially ionized regions with electron densities of a few hundred per centimeter cubed.

  • 5. Barrado, David
    et al.
    Mollière, Paul
    Patapis, Polychronis
    Min, Michiel
    Tremblin, Pascal
    Ardevol Martinez, Francisco
    Whiteford, Niall
    Vasist, Malavika
    Argyriou, Ioannis
    Samland, Matthias
    Lagage, Pierre-Olivier
    Decin, Leen
    Waters, Rens
    Henning, Thomas
    Morales-Calderón, María
    Guedel, Manuel
    Vandenbussche, Bart
    Absil, Olivier
    Baudoz, Pierre
    Boccaletti, Anthony
    Bouwman, Jeroen
    Cossou, Christophe
    Coulais, Alain
    Crouzet, Nicolas
    Gastaud, René
    Glasse, Alistair
    Glauser, Adrian M.
    Kamp, Inga
    Kendrew, Sarah
    Krause, Oliver
    Lahuis, Fred
    Mueller, Michael
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Pye, John
    Rouan, Daniel
    Royer, Pierre
    Scheithauer, Silvia
    Waldmann, Ingo
    Colina, Luis
    van Dishoeck, Ewine F.
    Ray, Tom
    Östlin, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Wright, Gillian
    15NH3 in the atmosphere of a cool brown dwarf2023Ingår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 624, nr 7991, s. 263-266Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Brown dwarfs serve as ideal laboratories for studying the atmospheres of giant exoplanets on wide orbits, as the governing physical and chemical processes within them are nearly identical. Understanding the formation of gas-giant planets is challenging, often involving the endeavour to link atmospheric abundance ratios, such as the carbon-to-oxygen (C/O) ratio, to formation scenarios. However, the complexity of planet formation requires further tracers, as the unambiguous interpretation of the measured C/O ratio is fraught with complexity. Isotope ratios, such as deuterium to hydrogen and 14N/15N, offer a promising avenue to gain further insight into this formation process, mirroring their use within the Solar System. For exoplanets, only a handful of constraints on 12C/13C exist, pointing to the accretion of 13C-rich ice from beyond the CO iceline of the disks. Here we report on the mid-infrared detection of the 14NH3 and 15NH3 isotopologues in the atmosphere of a cool brown dwarf with an effective temperature of 380 K in a spectrum taken with the Mid-Infrared Instrument (MIRI) of JWST. As expected, our results reveal a 14N/15N value consistent with star-like formation by gravitational collapse, demonstrating that this ratio can be accurately constrained. Because young stars and their planets should be more strongly enriched in the 15N isotope, we expect that 15NH3 will be detectable in several cold, wide-separation exoplanets. 

  • 6. Barros, S. C. C.
    et al.
    Akinsanmi, B.
    Boue, G.
    Smith, A. M. S.
    Laskar, J.
    Ulmer-Moll, S.
    Lillo-Box, J.
    Queloz, D.
    Collier Cameron, A.
    Sousa, S. G.
    Ehrenreich, D.
    Hooton, M. J.
    Bruno, G.
    Demory, B.-O.
    Correia, A. C. M.
    Demangeon, O. D. S.
    Wilson, T. G.
    Bonfanti, A.
    Hoyer, S.
    Alibert, Y.
    Alonso, R.
    Anglada Escude, G.
    Barbato, D.
    Barczy, T.
    Barrado, D.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Benz, W.
    Bergomi, M.
    Billot, N.
    Bonfils, X.
    Bouchy, F.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Broeg, C.
    Cabrera, J.
    Cessa, V.
    Charnoz, S.
    Damme, C. C.
    Davies, M. B.
    Deleuil, M.
    Deline, A.
    Delrez, L.
    Erikson, A.
    Fortier, A.
    Fossati, L.
    Fridlund, M.
    Gandolfi, D.
    García Muñoz, A.
    Gillon, M.
    Güdel, M.
    Isaak, K. G.
    Heng, K.
    Kiss, L.
    Lecavelier des Etangs, A.
    Lendl, M.
    Lovis, C.
    Magrin, D.
    Nascimbeni, V.
    Maxted, P. F. L.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ottensamer, R.
    Pagano, I.
    Pallé, E.
    Parviainen, H.
    Peter, G.
    Piotto, G.
    Pollacco, D.
    Ragazzoni, R.
    Rando, N.
    Rauer, H.
    Ribas, I.
    Santos, N. C.
    Scandariato, G.
    Ségransan, D.
    Simon, A. E.
    Steller, M.
    Szabó, Gy. M.
    Thomas, N.
    Udry, S.
    Ulmer, B.
    Van Grootel, V.
    Walton, N. A.
    Detection of the tidal deformation of WASP-103b at 3σ with CHEOPS2022Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 657, artikel-id A52Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Ultra-short period planets undergo strong tidal interactions with their host star which lead to planet deformation and orbital tidal decay.

    Aims. WASP-103b is the exoplanet with the highest expected deformation signature in its transit light curve and one of the shortest expected spiral-in times. Measuring the tidal deformation of the planet would allow us to estimate the second degree fluid Love number and gain insight into the planet's internal structure. Moreover, measuring the tidal decay timescale would allow us to estimate the stellar tidal quality factor, which is key to constraining stellar physics.

    Methods. We obtained 12 transit light curves of WASP-103b with the CHaracterising ExOplanet Satellite (CHEOPS) to estimate the tidal deformation and tidal decay of this extreme system. We modelled the high-precision CHEOPS transit light curves together with systematic instrumental noise using multi-dimensional Gaussian process regression informed by a set of instrumental parameters. To model the tidal deformation, we used a parametrisation model which allowed us to determine the second degree fluid Love number of the planet. We combined our light curves with previously observed transits of WASP-103b with the Hubble Space Telescope (HST) and Spitzer to increase the signal-to-noise of the light curve and better distinguish the minute signal expected from the planetary deformation.

    Results. We estimate the radial Love number of WASP-103b to be h(f) = 1.59(-0.53)(+0.45). This is the first time that the tidal deformation is directly detected (at 3 sigma) from the transit light curve of an exoplanet. Combining the transit times derived from CHEOPS, HST, and Spitzer light curves with the other transit times available in the literature, we find no significant orbital period variation for WASP-103b. However, the data show a hint of an orbital period increase instead of a decrease, as is expected for tidal decay. This could be either due to a visual companion star if this star is bound, the Applegate effect, or a statistical artefact.

    Conclusions. The estimated Love number of WASP-103b is similar to Jupiter's. This will allow us to constrain the internal structure and composition of WASP-103b, which could provide clues on the inflation of hot Jupiters. Future observations with James Webb Space Telescope can better constrain the radial Love number of WASP-103b due to their high signal-to-noise and the smaller signature of limb darkening in the infrared. A longer time baseline is needed to constrain the tidal decay in this system.

  • 7. Benz, W.
    et al.
    Broeg, C.
    Fortier, A.
    Rando, N.
    Beck, T.
    Beck, M.
    Queloz, D.
    Ehrenreich, D.
    Maxted, P. F. L.
    Isaak, K. G.
    Billot, N.
    Alibert, Y.
    Alonso, R.
    Antonio, C.
    Asquier, J.
    Bandy, T.
    Barczy, T.
    Barrado, D.
    Barros, S. C. C.
    Baumjohann, W.
    Bekkelien, A.
    Bergomi, M.
    Biondi, F.
    Bonfils, X.
    Borsato, L.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Busch, M.-D.
    Cabrera, J.
    Cessa, V.
    Charnoz, S.
    Chazelas, B.
    Collier Cameron, A.
    Corral Van Damme, C.
    Cortes, D.
    Davies, M. B.
    Deleuil, M.
    Deline, A.
    Delrez, L.
    Demangeon, O.
    Demory, B. O.
    Erikson, A.
    Farinato, J.
    Fossati, L.
    Fridlund, M.
    Futyan, D.
    Gandolfi, D.
    Garcia Munoz, A.
    Gillon, M.
    Guterman, P.
    Gutierrez, A.
    Hasiba, J.
    Heng, K.
    Hernandez, E.
    Hoyer, S.
    Kiss, L. L.
    Kovacs, Z.
    Kuntzer, T.
    Laskar, J.
    Lecavelier des Etangs, A.
    Lendl, M.
    Lopez, A.
    Lora, I.
    Lovis, C.
    Lueftinger, T.
    Magrin, D.
    Malvasio, L.
    Marafatto, L.
    Michaelis, H.
    de Miguel, D.
    Modrego, D.
    Munari, M.
    Nascimbeni, V.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ottacher, H.
    Ottensamer, R.
    Pagano, I.
    Palacios, R.
    Pall, E.
    Peter, G.
    Piazza, D.
    Piotto, G.
    Pizarro, A.
    Pollaco, D.
    Ragazzoni, R.
    Ratti, F.
    Rauer, H.
    Ribas, I.
    Rieder, M.
    Rohlfs, R.
    Safa, F.
    Salatti, M.
    Santos, N. C.
    Scandariato, G.
    Segransan, D.
    Simon, A. E.
    Smith, A. M. S.
    Sordet, M.
    Sousa, S. G.
    Steller, M.
    Szabo, G. M.
    Szoke, J.
    Thomas, N.
    Tschentscher, M.
    Udry, S.
    Van Grootel, V.
    Viotto, V.
    Walter, I.
    Walton, N. A.
    Wildi, F.
    Wolter, D.
    The CHEOPS mission2021Ingår i: Experimental astronomy, ISSN 0922-6435, E-ISSN 1572-9508, Vol. 51, s. 109-151Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The CHaracterising ExOPlanet Satellite (CHEOPS) was selected on October 19, 2012, as the first small mission (S-mission) in the ESA Science Programme and successfully launched on December 18, 2019, as a secondary passenger on a Soyuz-Fregat rocket from Kourou, French Guiana. CHEOPS is a partnership between ESA and Switzerland with important contributions by ten additional ESA Member States. CHEOPS is the first mission dedicated to search for transits of exoplanets using ultrahigh precision photometry on bright stars already known to host planets. As a follow-up mission, CHEOPS is mainly dedicated to improving, whenever possible, existing radii measurements or provide first accurate measurements for a subset of those planets for which the mass has already been estimated from ground-based spectroscopic surveys. The expected photometric precision will also allow CHEOPS to go beyond measuring only transits and to follow phase curves or to search for exo-moons, for example. Finally, by unveiling transiting exoplanets with high potential for in-depth characterisation, CHEOPS will also provide prime targets for future instruments suited to the spectroscopic characterisation of exoplanetary atmospheres. To reach its science objectives, requirements on the photometric precision and stability have been derived for stars with magnitudes ranging from 6 to 12 in the V band. In particular, CHEOPS shall be able to detect Earth-size planets transiting G5 dwarf stars (stellar radius of 0.9R(circle dot)) in the magnitude range 6 <= V <= 9 by achieving a photometric precision of 20 ppm in 6 hours of integration time. In the case of K-type stars (stellar radius of 0.7R(circle dot)) of magnitude in the range 9 <= V <= 12, CHEOPS shall be able to detect transiting Neptune-size planets achieving a photometric precision of 85 ppm in 3 hours of integration time. This precision has to be maintained over continuous periods of observation for up to 48 hours. This precision and stability will be achieved by using a single, frame-transfer, back-illuminated CCD detector at the focal plane assembly of a 33.5 cm diameter, on-axis Ritchey-Chretien telescope. The nearly 275 kg spacecraft is nadir-locked, with a pointing accuracy of about 1 arcsec rms, and will allow for at least 1 Gbit/day downlink. The sun-synchronous dusk-dawn orbit at 700 km altitude enables having the Sun permanently on the backside of the spacecraft thus minimising Earth stray light. A mission duration of 3.5 years in orbit is foreseen to enable the execution of the science programme. During this period, 20% of the observing time is available to the wider community through yearly ESA call for proposals, as well as through discretionary time approved by ESA's Director of Science. At the time of this writing, CHEOPS commissioning has been completed and CHEOPS has been shown to fulfill all its requirements. The mission has now started the execution of its science programme.

  • 8. Bjerkeli, P.
    et al.
    Liseau, R.
    Brinch, C.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Santangelo, G.
    Cabrit, S.
    Benedettini, M.
    Black, J. H.
    Herczeg, G.
    Justtanont, K.
    Kristensen, L. E.
    Larsson, Bengt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Nisini, B.
    Tafalla, M.
    Resolving the shocked gas in HH54 with Herschel CO line mapping at high spatial and spectral resolution2014Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 571, artikel-id A90Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The HH 54 shock is a Herbig-Haro object, located in the nearby Chamaeleon II cloud. Observed CO line profiles are due to a complex distribution in density, temperature, velocity, and geometry. Aims. Resolving the HH 54 shock wave in the far-infrared (FIR) cooling lines of CO constrain the kinematics, morphology, and physical conditions of the shocked region. Methods. We used the PACS and SPIRE instruments on board the Herschel space observatory to map the full FIR spectrum in a region covering the HH 54 shock wave. Complementary Herschel-HIFI, APEX, and Spitzer data are used in the analysis as well. The observed features in the line profiles are reproduced using a 3D radiative transfer model of a bow-shock, constructed with the Line Modeling Engine code (LIME). Results. The FIR emission is confined to the HH 54 region and a coherent displacement of the location of the emission maximum of CO with increasing J is observed. The peak positions of the high-J CO lines are shifted upstream from the lower J CO lines and coincide with the position of the spectral feature identified previously in CO(10-9) profiles with HIFI. This indicates a hotter molecular component in the upstream gas with distinct dynamics. The coherent displacement with increasing J for CO is consistent with a scenario where IRAS12500 - 7658 is the exciting source of the flow, and the 180 K bow-shock is accompanied by a hot (800 K) molecular component located upstream from the apex of the shock and blueshifted by -7 km s(-1). The spatial proximity of this knot to the peaks of the atomic fine-structure emission lines observed with Spitzer and PACS ([O I]63, 145 mu m) suggests that it may be associated with the dissociative shock as the jet impacts slower moving gas in the HH 54 bow-shock.

  • 9. Boldog, Á.
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Walton, N. A.
    Glancing through the debris disk: Photometric analysis of DE Boo with CHEOPS star2023Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 671, artikel-id A127Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims. DE Boo is a unique system, with an edge-on view through the debris disk around the star. The disk, which is analogous to the Kuiper belt in the Solar System, was reported to extend from 74 to 84 AU from the central star. The high photometric precision of the Characterising Exoplanet Satellite (CHEOPS) provided an exceptional opportunity to observe small variations in the light curve due to transiting material in the disk. This is a unique chance to investigate processes in the debris disk.

    Methods. Photometric observations of DE Boo of a total of four days were carried out with CHEOPS. Photometric variations due to spots on the stellar surface were subtracted from the light curves by applying a two-spot model and a fourth-order polynomial. The photometric observations were accompanied by spectroscopic measurements with the 1m RCC telescope at Piszkéstető and with the SOPHIE spectrograph in order to refine the astrophysical parameters of DE Boo.

    Results. We present a detailed analysis of the photometric observation of DE Boo. We report the presence of nonperiodic transient features in the residual light curves with a transit duration of 0.3–0.8 days. We calculated the maximum distance of the material responsible for these variations to be 2.47 AU from the central star, much closer than most of the mass of the debris disk. Furthermore, we report the first observation of flaring events in this system.

    Conclusions. We interpreted the transient features as the result of scattering in an inner debris disk around DE Boo. The processes responsible for these variations were investigated in the context of interactions between planetesimals in the system.

  • 10. Bonfanti, A.
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Zingales, T.
    Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley2024Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 682, artikel-id A66Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context

    TOI-732 is an M dwarf hosting two transiting planets that are located on the two opposite sides of the radius valley. Inferring a reliable demographics for this type of systems is key to understanding their formation and evolution mechanisms.

    Aims

    By doubling the number of available space-based observations and increasing the number of radial velocity (RV) measurements, we aim at refining the parameters of TOI-732 b and c. We also use the results to study the slope of the radius valley and the density valley for a well-characterised sample of M-dwarf exoplanets.

    Methods

    We performed a global Markov chain Monte Carlo analysis by jointly modelling ground-based light curves and CHEOPS and TESS observations, along with RV time series both taken from the literature and obtained with the MAROON-X spectrograph. The slopes of the M-dwarf valleys were quantified via a support vector machine (SVM) procedure.

    Results

    TOI-732b is an ultrashort-period planet (P = 0.76837931-0.00000042+0.0000039 days) with a radius Rb = 1.325-0.058+0.057R, a mass Mb = 2.46 ± 0.19 M, and thus a mean density ρb = 5.8-0.8+1.0 g cm-3, while the outer planet at P = 12.252284 ± 0.000013 days has Rc = 2.39-0.11+0.10RMc = 8.04-0.48+0.50M, and thus ρc = 3.24-0.43+0.55 g cm-3. Even with respect to the most recently reported values, this work yields uncertainties on the transit depths and on the RV semi-amplitudes that are smaller up to a factor of ~1.6 and ~2.4 for TOI-732 b and c, respectively. Our calculations for the interior structure and the location of the planets in the mass-radius diagram lead us to classify TOI-732 b as a super-Earth and TOI-732 c as a mini-Neptune. Following the SVM approach, we quantified d log Rp,valley / d logP = -0.065-0.013+0.024, which is flatter than for Sun-like stars. In line with former analyses, we note that the radius valley for M-dwarf planets is more densely populated, and we further quantify the slope of the density valley as d log ρ^valley / d log P = -0.02-0.04+0.12.

    Conclusions

    Compared to FGK stars, the weaker dependence of the position of the radius valley on the orbital period might indicate that the formation shapes the radius valley around M dwarfs more strongly than the evolution mechanisms.

  • 11. Bonfanti, A.
    et al.
    Delrez, L.
    Hooton, M. J.
    Wilson, T. G.
    Fossati, L.
    Alibert, Y.
    Hoyer, S.
    Mustill, A. J.
    Osborn, H. P.
    Adibekyan, V.
    Gandolfi, D.
    Salmon, S.
    Sousa, S. G.
    Tuson, A.
    Van Grootel, V.
    Cabrera, J.
    Nascimbeni, V.
    Maxted, P. F. L.
    Barros, S. C. C.
    Billot, N.
    Bonfils, X.
    Borsato, L.
    Broeg, C.
    Davies, M. B.
    Deleuil, M.
    Demangeon, O. D. S.
    Fridlund, M.
    Lacedelli, G.
    Lendl, M.
    Persson, C.
    Santos, N. C.
    Scandariato, G.
    Szabo, Gy M.
    Collier Cameron, A.
    Udry, S.
    Benz, W.
    Beck, M.
    Ehrenreich, D.
    Fortier, A.
    Isaak, K. G.
    Queloz, D.
    Alonso, R.
    Asquier, J.
    Bandy, T.
    Barczy, T.
    Barrado, D.
    Barragan, O.
    Baumjohann, W.
    Beck, T.
    Bekkelien, A.
    Bergomi, M.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Busch, M.-D.
    Cessa, V.
    Charnoz, S.
    Chazelas, B.
    Corral Van Damme, C.
    Demory, B.-O.
    Erikson, A.
    Farinato, J.
    Futyan, D.
    Garcia Munoz, A.
    Gillon, M.
    Guedel, M.
    Guterman, P.
    Hasiba, J.
    Heng, K.
    Hernandez, E.
    Kiss, L.
    Kuntzer, T.
    Laskar, J.
    Lecavelier des Etangs, A.
    Lovis, C.
    Magrin, D.
    Malvasio, L.
    Marafatto, L.
    Michaelis, H.
    Munari, M.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ottacher, H.
    Ottensamer, R.
    Pagano, I.
    Palle, E.
    Peter, G.
    Piazza, D.
    Piotto, G.
    Pollacco, D.
    Ragazzoni, R.
    Rando, N.
    Ratti, F.
    Rauer, H.
    Ribas, I.
    Rieder, M.
    Rohlfs, R.
    Safa, F.
    Salatti, M.
    Segransan, D.
    Simon, A. E.
    Smith, A. M. S.
    Sordet, M.
    Steller, M.
    Thomas, N.
    Tschentscher, M.
    Van Eylen, V.
    Viotto, V.
    Walter, I.
    Walton, N. A.
    Wildi, F.
    Wolter, D.
    CHEOPS observations of the HD 108236 planetary system: a fifth planet, improved ephemerides, and planetary radii2021Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 646, artikel-id A157Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The detection of a super-Earth and three mini-Neptunes transiting the bright (V = 9.2 mag) star HD 108236 (also known as TOI-1233) was recently reported on the basis of TESS and ground-based light curves.

    Aims. We perform a first characterisation of the HD 108236 planetary system through high-precision CHEOPS photometry and improve the transit ephemerides and system parameters.

    Methods. We characterise the host star through spectroscopic analysis and derive the radius with the infrared flux method. We constrain the stellar mass and age by combining the results obtained from two sets of stellar evolutionary tracks. We analyse the available TESS light curves and one CHEOPS transit light curve for each known planet in the system.

    Results. We find that HD 108236 is a Sun-like star with R-star = 0.877 +/- 0.008 R-circle dot, M-star = 0.869(-0.048)(+0.050)M(circle dot), and an age of 6.7(-5.1)(+4.0) Gyr. We report the serendipitous detection of an additional planet, HD 108236 f, in one of the CHEOPS light curves. For this planet, the combined analysis of the TESS and CHEOPS light curves leads to a tentative orbital period of about 29.5 days. From the light curve analysis, we obtain radii of 1.615 +/- 0.051, 2.071 +/- 0.052, 2.539(-0.065)(+0.062), 3.083 +/- 0.052, and 2.017(-0.057)(+0.052) R-circle plus for planets HD 108236 b to HD 108236 f, respectively. These values are in agreement with previous TESS-based estimates, but with an improved precision of about a factor of two. We perform a stability analysis of the system, concluding that the planetary orbits most likely have eccentricities smaller than 0.1. We also employ a planetary atmospheric evolution framework to constrain the masses of the five planets, concluding that HD 108236 b and HD 108236 c should have an Earth-like density, while the outer planets should host a low mean molecular weight envelope.

    Conclusions. The detection of the fifth planet makes HD 108236 the third system brighter than V = 10 mag to host more than four transiting planets. The longer time span enables us to significantly improve the orbital ephemerides such that the uncertainty on the transit times will be of the order of minutes for the years to come. A comparison of the results obtained from the TESS and CHEOPS light curves indicates that for a V similar to 9 mag solar-like star and a transit signal of similar to 500 ppm, one CHEOPS transit light curve ensures the same level of photometric precision as eight TESS transits combined, although this conclusion depends on the length and position of the gaps in the light curve.

  • 12. Bonfanti, A.
    et al.
    Florén, Hans Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Walton, N. A.
    TOI-1055 b: Neptunian planet characterised with HARPS, TESS, and CHEOPS2023Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 671, artikel-id L8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. TOI-1055 is a Sun-like star known to host a transiting Neptune-sized planet on a 17.5-day orbit (TOI-1055 b). Radial velocity (RV) analyses carried out by two independent groups using nearly the same set of HARPS spectra have provided measurements of planetary masses that differ by ∼2σ.

    Aims. Our aim in this work is to solve the inconsistency in the published planetary masses by significantly extending the set of HARPS RV measurements and employing a new analysis tool that is able to account and correct for stellar activity. Our further aim was to improve the precision on measurements of the planetary radius by observing two transits of the planet with the CHEOPS space telescope.

    Methods. We fit a skew normal function to each cross correlation function extracted from the HARPS spectra to obtain RV measurements and hyperparameters to be used for the detrending. We evaluated the correlation changes of the hyperparameters along the RV time series using the breakpoint technique. We performed a joint photometric and RV analysis using a Markov chain Monte Carlo scheme to simultaneously detrend the light curves and the RV time series.

    Results. We firmly detected the Keplerian signal of TOI-1055 b, deriving a planetary mass of Mb = 20.4−2.5+2.6 M (∼12%). This value is in agreement with one of the two estimates in the literature, but it is significantly more precise. Thanks to the TESS transit light curves combined with exquisite CHEOPS photometry, we also derived a planetary radius of Rb = 3.490−0.064+0.070 R (∼1.9%). Our mass and radius measurements imply a mean density of ρb = 2.65−0.35+0.37 g cm−3 (∼14%). We further inferred the planetary structure and found that TOI-1055 b is very likely to host a substantial gas envelope with a mass of 0.41−0.20+0.34 M and a thickness of 1.05−0.29+0.30 R.

    Conclusions. Our RV extraction combined with the breakpoint technique has played a key role in the optimal removal of stellar activity from the HARPS time series, enabling us to solve the tension in the planetary mass values published so far for TOI-1055 b.

  • 13. Borsato, L.
    et al.
    Piotto, G.
    Gandolfi, D.
    Nascimbeni, V
    Lacedelli, G.
    Marzari, F.
    Billot, N.
    Maxted, P. F. L.
    Sousa, S.
    Cameron, A. C.
    Bonfanti, A.
    Wilson, T. G.
    Serrano, L. M.
    Garai, Z.
    Alibert, Y.
    Alonso, R.
    Asquier, J.
    Bárczy, T.
    Bandy, T.
    Barrado, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Benz, W.
    Bonfils, X.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Broeg, C.
    Cabrera, J.
    Charnoz, S.
    Csizmadia, S.
    Davies, M. B.
    Deleuil, M.
    Delrez, L.
    Demangeon, O.
    Demory, B-O
    des Etangs, A. L.
    Ehrenreich, D.
    Erikson, A.
    Escudé, G. A.
    Fortier, A.
    Fossati, L.
    Fridlund, M.
    Gillon, M.
    Guedel, M.
    Hasiba, J.
    Heng, K.
    Hoyer, S.
    Isaak, K. G.
    Kiss, L.
    Kopp, E.
    Laskar, J.
    Lendl, M.
    Lovis, C.
    Magrin, D.
    Munari, M.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ottensamer, R.
    Pagano, I
    Pallé, E.
    Peter, G.
    Pollacco, D.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Rauer, H.
    Ribas, I
    Ségransan, D.
    Santos, N. C.
    Scandariato, G.
    Simon, A.
    Smith, A. M. S.
    Steller, M.
    Szabó, G.
    Thomas, N.
    Udry, S.
    Van Grootel, V.
    Walton, N.
    Exploiting timing capabilities of the CHEOPS mission with warm-Jupiter planets2021Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 506, nr 3, s. 3810-3830Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present 17 transit light curves of seven known warm-Jupiters observed with the CHaracterising ExOPlanet Satellite (CHEOPS). The light curves have been collected as part of the CHEOPS Guaranteed Time Observation (GTO) program that searches for transit-timing variation (TTV) of warm-Jupiters induced by a possible external perturber to shed light on the evolution path of such planetary systems. We describe the CHEOPS observation process, from the planning to the data analysis. In this work, we focused on the timing performance of CHEOPS, the impact of the sampling of the transit phases, and the improvement we can obtain by combining multiple transits together. We reached the highest precision on the transit time of about 13–16 s for the brightest target (WASP-38, G = 9.2) in our sample. From the combined analysis of multiple transits of fainter targets with G ≥ 11, we obtained a timing precision of ∼2 min. Additional observations with CHEOPS, covering a longer temporal baseline, will further improve the precision on the transit times and will allow us to detect possible TTV signals induced by an external perturber.

  • 14.
    Brandeker, Alexis
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Cataldi, Gianni
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Vandenbussche, B.
    Acke, B.
    Barlow, M. J.
    Blommaert, J. A. D. L.
    Cohen, M.
    Dent, W. R. F.
    Dominik, C.
    Di Francesco, J.
    Fridlund, M.
    Gear, W. K.
    Glauser, A. M.
    Greaves, J. S.
    Harvey, P. M.
    Heras, A. M.
    Hogerheijde, M. R.
    Holland, W. S.
    Huygen, R.
    Ivison, R. J.
    Leeks, S. J.
    Lim, T. L.
    Liseau, R.
    Matthews, B. C.
    Pantin, E.
    Pilbratt, G. L.
    Royer, P.
    Sibthorpe, B.
    Waelkens, C.
    Walker, H. J.
    Herschel detects oxygen in the beta Pictoris debris disk2016Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 591, artikel-id A27Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The young star beta Pictoris is well known for its dusty debris disk produced through collisional grinding of planetesimals, kilometre-sized bodies in orbit around the star. In addition to dust, small amounts of gas are also known to orbit the star; this gas is likely the result of vaporisation of violently colliding dust grains. The disk is seen edge on and from previous absorption spectroscopy we know that the gas is very rich in carbon relative to other elements. The oxygen content has been more difficult to assess, however, with early estimates finding very little oxygen in the gas at a C/O ratio that is 20x higher than the cosmic value. A C/O ratio that high is difficult to explain and would have far-reaching consequences for planet formation. Here we report on observations by the far-infrared space telescope Herschel, using PACS, of emission lines from ionised carbon and neutral oxygen. The detected emission from C+ is consistent with that previously reported observed by the HIFI instrument on Herschel, while the emission from O is hard to explain without assuming a higher density region in the disk, perhaps in the shape of a clump or a dense torus required to sufficiently excite the O atoms. A possible scenario is that the C/O gas is produced by the same process responsible for the CO clump recently observed by the Atacama Large Millimeter/submillimeter Array in the disk and that the redistribution of the gas takes longer than previously assumed. A more detailed estimate of the C/O ratio and the mass of O will have to await better constraints on the C/O gas spatial distribution.

  • 15.
    Brandeker, Alexis
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Cataldi, Gianni
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Vandenbussche, Bart
    Acke, Bram
    Barlow, Michael J.
    Blommaert, Joris A. D. L.
    Cohen, Martin
    Dent, William R. F.
    Dominik, Carsten
    Di Francesco, James
    Fridlund, Malcolm
    Gear, Walter K.
    Glauser, Adrian Michael
    Greaves, Jane S.
    Harvey, Paul M.
    Heras, Ana M.
    Hogerheijde, Michiel R.
    Holland, Wayne S.
    Huygen, Rik
    Ivison, Rob J.
    Leeks, Sarah J.
    Lim, Tanya L.
    Liseau, René
    Matthews, Brenda C.
    Pantin, Eric
    Pilbratt, Göran L.
    Royer, Pierre
    Sibthorpe, Bruce
    Waelkens, Christoffel
    Walker, Helen J.
    Herschel detects oxygen in the β Pictoris debris diskIngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Artikel i tidskrift (Refereegranskat)
  • 16.
    Brandeker, Alexis
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Florén, Hans Gustav Axel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    The HD 93963 A transiting system: A 1.04d super-Earth and a 3.65 d sub-Neptune discovered by TESS and CHEOPS2022Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 667, artikel-id A1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the discovery of two small planets transiting HD 93963A (TOI-1797), a GOV star (M* = 1.109 ± 0.043MR* = 1.043 ± 0.009 R) in a visual binary system. We combined TESS and CHEOPS space-borne photometry with MuSCAT 2 ground-based photometry, ‘Alopeke and PHARO high-resolution imaging, TRES and FIES reconnaissance spectroscopy, and SOPHIE radial velocity measurements. We validated and spectroscopically confirmed the outer transiting planet HD 93963 A c, a sub-Neptune with an orbital period of Pc ≈ 3.65 d that was reported to be a TESS object of interest (TOI) shortly after the release of Sector 22 data. HD 93963 A c has amass of Mc = 19.2 ± 4.1 M and a radius of Rc = 3.228 ± 0.059 R, implying a mean density of ρc = 3.1 ± 0.7 g cm-3. The inner object, HD 93963 A b, is a validated 1.04 d ultra-short period (USP) transiting super-Earth that we discovered in the TESS light curve and that was not listed as a TOI, owing to the low significance of its signal (TESS signal-to-noise ratio ≈6.7, TESS + CHEOPS combined transit depth Db = 141.5−8.3+8.5 ppm). We intensively monitored the star with CHEOPS by performing nine transit observations to confirm the presence of the inner planet and validate the system. HD 93963 A b is the first small (Rb = 1.35 ± 0.042 R) USP planet discovered and validated by TESS and CHEOPS. Unlike planet c, HD 93963 Ab is not significantly detected in our radial velocities (Mb = 7.8 ± 3.2 M). The two planets are on either side of the radius valley, implying that they could have undergone completely different evolution processes. We also discovered a linear trend in our Doppler measurements, suggesting the possible presence of a long-period outer planet. With a V-band magnitude of 9.2, HD 93963 A is among the brightest stars known to host a USP planet, making it one of the most favourable targets for precise mass measurement via Doppler spectroscopy and an important laboratory to test formation, evolution, and migration models of planetary systems hosting ultra-short period planets.

  • 17.
    Brandeker, Alexis
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Heng, K.
    Lendl, M.
    Patel, Jayshil Ashokkumar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Morris, B. M.
    Broeg, C.
    Guterman, P.
    Beck, M.
    Maxted, P. F. L.
    Demangeon, O.
    Delrez, L.
    Demory, B-O
    Kitzmann, D.
    Santos, N. C.
    Singh, V
    Alibert, Y.
    Alonso, R.
    Anglada, G.
    Barczy, T.
    Barrado y Navascues, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, T.
    Benz, W.
    Billot, N.
    Bonfils, X.
    Bruno, G.
    Cabrera, J.
    Charnoz, S.
    Collier Cameron, A.
    van Damme, C. Corral
    Csizmadia, Sz
    Davies, M. B.
    Deleuil, M.
    Deline, A.
    Ehrenreich, D.
    Erikson, A.
    Farinato, J.
    Fortier, A.
    Fossati, L.
    Fridlund, M.
    Gandolfi, D.
    Gillon, M.
    Guedel, M.
    Hoyer, S.
    Isaak, K. G.
    Kiss, L.
    Laskar, J.
    Lecavelier des Etangs, A.
    Lovis, C.
    Luntzer, A.
    Magrin, D.
    Nascimbeni, V
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ottensamer, R.
    Pagano, I
    Pallé, E.
    Peter, G.
    Piotto, G.
    Pollacco, D.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Rauer, H.
    Ribas, I
    Scandariato, G.
    Ségransan, D.
    Simon, A. E.
    Smith, A. M. S.
    Sousa, S. G.
    Steller, M.
    Szabó, G. M.
    Thomas, N.
    Udry, S.
    Van Grootel, V.
    Walton, N.
    Wolter, D.
    CHEOPS geometric albedo of the hot Jupiter HD 209458 b2022Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 659, artikel-id L4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the detection of the secondary eclipse of the hot Jupiter HD 209458 b in optical/visible light using the CHEOPS space telescope. Our measurement of 20.4−3.3+3.2 parts per million translates into a geometric albedo of Ag = 0.096 ± 0.016. The previously estimated dayside temperature of about 1500 K implies that our geometric albedo measurement consists predominantly of reflected starlight and is largely uncontaminated by thermal emission. This makes the present result one of the most robust measurements of Ag for any exoplanet. Our calculations of the bandpass-integrated geometric albedo demonstrate that the measured value of Ag is consistent with a cloud-free atmosphere, where starlight is reflected via Rayleigh scattering by hydrogen molecules, and the water and sodium abundances are consistent with stellar metallicity. We predict that the bandpass-integrated TESS geometric albedo is too faint to detect and that a phase curve of HD 209458 b observed by CHEOPS would have a distinct shape associated with Rayleigh scattering if the atmosphere is indeed cloud free.

  • 18.
    Brandeker, Alexis
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Lendl, M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Patel, Jayshil Ashokkumar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    55 Cancri e's occultation captured with CHEOPS2023Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 669, artikel-id A64Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Past occultation and phase-curve observations of the ultra-short period super-Earth 55 Cnc e obtained at visible and infrared wavelengths have been challenging to reconcile with a planetary reflection and emission model. In this study, we analyse a set of 41 occultations obtained over a two-year timespan with the CHEOPS satellite. We report the detection of 55 Cnc e’s occultation with an average depth of 12 ± 3 ppm. We derive a corresponding 2σ upper limit on the geometric albedo of Ag < 0.55 once decontaminated from the thermal emission measured by Spitzer at 4.5 µm. CHEOPS’s photometric performance enables, for the first time, the detection of individual occultations of this super-Earth in the visible and identifies short-timescale photometric corrugations likely induced by stellar granulation. We also find a clear 47.3-day sinusoidal pattern in the time-dependent occultation depths that we are unable to relate to stellar noise, nor instrumental systematics, but whose planetary origin could be tested with upcoming JWST occultation observations of this iconic super-Earth.

  • 19.
    Brandeker, Alexis
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    A new dynamical modeling of the WASP-47 system with CHEOPS observations star2023Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 673, artikel-id A42Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Among the hundreds of known hot Jupiters (HJs), only five have been found to have companions on short-period orbits. Within this rare class of multiple planetary systems, the architecture of WASP-47 is unique, hosting an HJ (planet-b) with both an inner and an outer sub-Neptunian mass companion (-e and -d, respectively) as well as an additional non-transiting, long-period giant (-c). The small period ratio between planets -b and -d boosts the transit time variation (TTV) signal, making it possible to reliably measure the masses of these planets in synergy with the radial velocity (RV) technique. In this paper, we present new space- and ground-based photometric data of WASP-47b and WASP-47-d, including 11 unpublished light curves from the ESA mission CHaracterising ExOPlanet Satellite (CHEOPS). We analyzed the light curves in a homogeneous way together with all the publicly available data to carry out a global N-body dynamical modeling of the TTV and RV signals. We retrieved, among other parameters, a mass and density for planet -d of Md = 15.5 ± 0.8 M and ρd = 1.69 ± 0.22 g cm−3, which is in good agreement with the literature and consistent with a Neptune-like composition. For the inner planet (-e), we found a mass and density of Me = 9.0 ± 0.5 M and ρe = 8.1 ± 0.5 g cm−3, suggesting an Earth-like composition close to other ultra-hot planets at similar irradiation levels. Though this result is in agreement with previous RV plus TTV studies, it is not in agreement with the most recent RV analysis (at 2.8σ), which yielded a lower density compatible with a pure silicate composition. This discrepancy highlights the still unresolved issue of suspected systematic offsets between RV and TTV measurements. In this paper, we also significantly improve the orbital ephemerides of all transiting planets, which will be crucial for any future follow-up.

  • 20.
    Brandeker, Alexis
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Connecting photometric and spectroscopic granulation signals with CHEOPS and ESPRESSO2023Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 670, artikel-id A24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Stellar granulation generates fluctuations in photometric and spectroscopic data whose properties depend on the stellar type, composition, and evolutionary state. Characterizing granulation is key for understanding stellar atmospheres and detecting planets.

    Aims. We aim to detect the signatures of stellar granulation, link spectroscopic and photometric signatures of convection for main-sequence stars, and test predictions from 3D hydrodynamic models.

    Methods. For the first time, we observed two bright stars (Teff = 5833 and 6205 K) with high-precision observations taken simultaneously with CHEOPS and ESPRESSO. We analyzed the properties of the stellar granulation signal in each individual dataset. We compared them to Kepler observations and 3D hydrodynamic models. While isolating the granulation-induced changes by attenuating and filtering the p-mode oscillation signals, we studied the relationship between photometric and spectroscopic observables.

    Results. The signature of stellar granulation is detected and precisely characterized for the hotter F star in the CHEOPS and ESPRESSO observations. For the cooler G star, we obtain a clear detection in the CHEOPS dataset only. The TESS observations are blind to this stellar signal. Based on CHEOPS observations, we show that the inferred properties of stellar granulation are in agreement with both Kepler observations and hydrodynamic models. Comparing their periodograms, we observe a strong link between spectroscopic and photometric observables. Correlations of this stellar signal in the time domain (flux versus radial velocities, RV) and with specific spectroscopic observables (shape of the cross-correlation functions) are however difficult to isolate due to S/N dependent variations.

    Conclusions. In the context of the upcoming PLATO mission and the extreme precision RV surveys, a thorough understanding of the properties of the stellar granulation signal is needed. The CHEOPS and ESPRESSO observations pave the way for detailed analyses of this stellar process.

  • 21.
    Brandeker, Alexis
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Refining the properties of the TOI-178 system with CHEOPS and TESS2023Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 678, artikel-id A200Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The TOI-178 system consists of a nearby late K-dwarf transited by six planets in the super-Earth to mini-Neptune regime, with radii ranging from ~1.1 to 2.9 R and orbital periods between 1.9 and 20.7 days. All planets but the innermost one form a chain of Laplace resonances. Mass estimates derived from a preliminary radial velocity (RV) dataset suggest that the planetary densities do not decrease in a monotonic way with the orbital distance to the star, contrary to what one would expect based on simple formation and evolution models.

    Aims. To improve the characterisation of this key system and prepare for future studies (in particular with JWST), we performed a detailed photometric study based on 40 new CHEOPS visits, one new TESS sector, and previously published CHEOPS, TESS, and NGTS data.

    Methods. First we updated the parameters of the host star using the new parallax from Gaia EDR3. We then performed a global analysis of the 100 transits contained in our data to refine the physical and orbital parameters of the six planets and study their transit timing variations (TTVs). We also used our extensive dataset to place constraints on the radii and orbital periods of potential additional transiting planets in the system.

    Results. Our analysis significantly refines the transit parameters of the six planets, most notably their radii, for which we now obtain relative precisions of ≲3%, with the exception of the smallest planet, b, for which the precision is 5.1%. Combined with the RV mass estimates, the measured TTVs allow us to constrain the eccentricities of planets c to g, which are found to be all below 0.02, as expected from stability requirements. Taken alone, the TTVs also suggest a higher mass for planet d than that estimated from the RVs, which had been found to yield a surprisingly low density for this planet. However, the masses derived from the current TTV dataset are very prior-dependent, and further observations, over a longer temporal baseline, are needed to deepen our understanding of this iconic planetary system.

  • 22.
    Brandeker, Alexis
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    The stable climate of KELT-9b2022Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 666, artikel-id A118Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Even among the most irradiated gas giants, so-called ultra-hot Jupiters, KELT-9b stands out as the hottest planet thus far discovered with a dayside temperature of over 4500 K. At these extreme irradiation levels, we expect an increase in heat redistribution efficiency and a low Bond albedo owed to an extended atmosphere with molecular hydrogen dissociation occurring on the planetary dayside. We present new photometric observations of the KELT-9 system throughout 4 full orbits and 9 separate occultations obtained by the 30 cm space telescope CHEOPS. The CHEOPS bandpass, located at optical wavelengths, captures the peak of the thermal emission spectrum of KELT-9b. In this work we simultaneously analyse CHEOPS phase curves along with public phase curves from TESS and Spitzer to infer joint constraints on the phase curve variation, gravity-darkened transits, and occultation depth in three bandpasses, as well as derive 2D temperature maps of the atmosphere at three different depths. We find a day-night heat redistribution efficiency of ~0.3 which confirms expectations of enhanced energy transfer to the planetary nightside due to dissociation and recombination of molecular hydrogen. We also calculate a Bond albedo consistent with zero. We find no evidence of variability of the brightness temperature of the planet, excluding variability greater than 1%

  • 23. Cataldi, Gianni
    et al.
    Aikawa, Yuri
    Iwasaki, Kazunari
    Marino, Sebastian
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Hales, Antonio
    Henning, Thomas
    Higuchi, Aya E.
    Hughes, A. Meredith
    Janson, Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Kral, Quentin
    Matra, Luca
    Moor, Attila
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Redfield, Seth
    Roberge, Aki
    Primordial or Secondary? Testing Models of Debris Disk Gas with ALMA*2023Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 951, nr 2, artikel-id 111Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The origin and evolution of gas in debris disks are still not well understood. Secondary gas production from cometary material or a primordial origin have been proposed. So far, observations have mostly concentrated on CO, with only a few C observations available. We overview the C and CO content of debris disk gas and test state-of-the-art models. We use new and archival Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO and C i emission, complemented by C ii data from Herschel, for a sample of 14 debris disks. This expands the number of disks with ALMA measurements of both CO and C i by 10 disks. We present new detections of C i emission toward three disks: HD 21997, HD 121191, and HD 121617. We use a simple disk model to derive gas masses and column densities. We find that current state-of-the-art models of secondary gas production overpredict the C-0 content of debris disk gas. This does not rule out a secondary origin, but might indicate that the models require an additional C removal process. Alternatively, the gas might be produced in transient events rather than a steady-state collisional cascade. We also test a primordial gas origin by comparing our results to a simplified thermochemical model. This yields promising results, but more detailed work is required before a conclusion can be reached. Our work demonstrates that the combination of C and CO data is a powerful tool to advance our understanding of debris disk gas.

  • 24.
    Cataldi, Gianni
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Chen, C. H.
    Dent, W. R. F.
    Kamp, I.
    Roberge, A.
    Vandenbussche, B.
    Constraints on the gas content of the Fomalhaut debris belt Can gas-dust interactions explain the belt's morphology?2015Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 574, artikel-id L1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The 440 Myr old main-sequence A-star Fomalhaut is surrounded by an eccentric debris belt with sharp edges. This sort of a morphology is usually attributed to planetary perturbations, but the orbit of the only planetary candidate detected so far, Fomalhaut b, is too eccentric to efficiently shape the belt. Alternative models that could account for the morphology without invoking a planet are stellar encounters and gas-dust interactions. Aims. We aim to test the possibility of gas-dust interactions as the origin of the observed morphology by putting upper limits on the total gas content of the Fomalhaut belt. Methods. We derive upper limits on the CII 158 mu m and 01 63 pint emission by using non detections from the Photocletector Array Camera and Spectrometer (PACS) onboard the Herschel Space Observatory. Line fluxes are converted into total gas mass using the non-local thermodynamic equilibrium (non-LTE) code RADEX. We consider two different cases for the elemental abundances of the gas: solar abundances and abundances similar to those observed for the gas in the beta Pictoris debris disc. Results. The gas mass is shown to be below the millimetre dust mass by a factor of at least similar to 3 (for solar abundances) respectively similar to 300 (for beta Pic-like abundances). Conclusions. The lack of gas co-spatial with the dust implies that gas-dust interactions cannot efficiently shape the Fomalhaut debris belt. The morphology is therefore more likely due to a yet unseen planet (Fomalhaut c) or stellar encounters.

  • 25.
    Cataldi, Gianni
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Larsson, Bengt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Liseau, R.
    Blommaert, J.
    Fridlund, M.
    Ivison, R.
    Pantin, E.
    Sibthorpe, B.
    Vandenbussche, B.
    Wu, Y.
    Herschel/HIFI observations of ionised carbon in the beta Pictoris debris disk2014Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 563, artikel-id A66Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The dusty debris disk around the similar to 20 Myr old main-sequence A-star beta Pictoris is known to contain gas. Evidence points towards a secondary origin of the gas as opposed to being a direct remnant from the initial protoplanetary disk, although the dominant gas production mechanism is so far not identified. The origin of the observed overabundance of C and O compared with solar abundances of metallic elements such as Na and Fe is also unclear. Aims. Our goal is to constrain the spatial distribution of C in the disk, and thereby the gas origin and its abundance pattern. Methods. We used the HIFI instrument on board the Herschel Space Observatory to observe and spectrally resolve C II emission at 158 mu m from the beta Pic debris disk. Assuming a disk in Keplerian rotation and a model for the line emission from the disk, we used the spectrally resolved line profile to constrain the spatial distribution of the gas. Results. We detect the C II 158 mu m emission. Modelling the shape of the emission line shows that most of the gas is located at about similar to 100 AU or beyond. We estimate a total C gas mass of 1.3(-0.5)(+1.3) x 10(2) M-circle plus (central 90% confidence interval). The data suggest that more gas is located on the south-west side of the disk than on the north-east side. The shape of the emission line is consistent with the hypothesis of a well mixed gas (constant C/Fe ratio throughout the disk). Assuming instead a spatial profile expected from a simplified accretion disk model, we found it to give a significantly poorer fit to the observations. Conclusions. Since the bulk of the gas is found outside 30 AU, we argue that the cometary objects known as falling evaporating bodies are probably not the dominant source of gas; production from grain-grain collisions or photodesorption seems more likely. The incompatibility of the observations with a simplified accretion disk model might favour a preferential depletion explanation for the overabundance of C and O, although it is unclear how much this conclusion is affected by the simplifications made. More stringent constraints on the spatial distribution will be available from ALMA observations of C I emission at 609 mu m.

  • 26.
    Cataldi, Gianni
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Thébault, Philippe
    Ahmed, Engy
    de Vries, Bernard L.
    Neubeck, Anna
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Singer, Kelsi
    Searching for biosignatures in exoplanetary impact ejectaIngår i: Astrobiology, ISSN 1531-1074, E-ISSN 1557-8070Artikel i tidskrift (Refereegranskat)
  • 27.
    Cataldi, Gianni
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Thébault, Philippe
    Singer, Kelsi
    Ahmed, Engy
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Royal Institute of Technology (KTH), Sweden.
    de Vries, Bernard L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. European Space Research and Technology Centre (ESA/ESTEC), The Netherlands.
    Neubeck, Anna
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Searching for Biosignatures in Exoplanetary Impact Ejecta2017Ingår i: Astrobiology, ISSN 1531-1074, E-ISSN 1557-8070, Vol. 17, nr 8, s. 721-746Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With the number of confirmed rocky exoplanets increasing steadily, their characterization and the search for exoplanetary biospheres are becoming increasingly urgent issues in astrobiology. To date, most efforts have concentrated on the study of exoplanetary atmospheres. Instead, we aim to investigate the possibility of characterizing an exoplanet (in terms of habitability, geology, presence of life, etc.) by studying material ejected from the surface during an impact event. For a number of impact scenarios, we estimate the escaping mass and assess its subsequent collisional evolution in a circumstellar orbit, assuming a Sun-like host star. We calculate the fractional luminosity of the dust as a function of time after the impact event and study its detectability with current and future instrumentation. We consider the possibility to constrain the dust composition, giving information on the geology or the presence of a biosphere. As examples, we investigate whether calcite, silica, or ejected microorganisms could be detected. For a 20km diameter impactor, we find that the dust mass escaping the exoplanet is roughly comparable to the zodiacal dust, depending on the exoplanet's size. The collisional evolution is best modeled by considering two independent dust populations, a spalled population consisting of nonmelted ejecta evolving on timescales of millions of years, and dust recondensed from melt or vapor evolving on much shorter timescales. While the presence of dust can potentially be inferred with current telescopes, studying its composition requires advanced instrumentation not yet available. The direct detection of biological matter turns out to be extremely challenging. Despite considerable difficulties (small dust masses, noise such as exozodiacal dust, etc.), studying dusty material ejected from an exoplanetary surface might become an interesting complement to atmospheric studies in the future.

  • 28.
    Cataldi, Gianni
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. National Astronomical Observatory of Japan, USA; Hungarian Academy of Sciences, Hungary.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Wu, Yanqin
    Chen, Christine
    Dents, William
    de Vries, Bernard L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. European Space Research and Technology Centre (ESA/ESTEC), The Netherlands.
    Kamp, Inga
    Liseau, René
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Pantin, Eric
    Roberge, Aki
    ALMA Resolves CI Emission from the beta Pictoris Debris Disk2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 861, nr 1, artikel-id 72Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The debris disk around beta Pictoris is known to contain gas. Previous ALMA observations revealed a CO belt at similar to 85 au with a distinct clump, interpreted as a location of enhanced gas production. Photodissociation converts CO into C and O within similar to 50 a. We resolve C I emission at 492 GHz using ALMA and study its spatial distribution. C I shows the same clump as seen for CO. This is surprising, as C is expected to quickly spread in azimuth. We derive a low C mass (between 5 x 10(-4) and 3.1 x 10(-3) MA(circle plus)), indicating that gas production started only recently (within similar to 5000 a). No evidence is seen for an atomic accretion disk inward of the CO belt, perhaps because the gas did not yet have time to spread radially. The fact that C and CO share the same asymmetry argues against a previously proposed scenario where the clump is due to an outward-migrating planet trapping planetesimals in a resonance, nor can the observations be explained by an eccentric planetesimal belt secularly forced by a planet. Instead, we suggest that the dust and gas disks should be eccentric. Such a configuration, we further speculate, might be produced by a recent tidal disruption event. Assuming that the disrupted body has had a CO mass fraction of 10%, its total mass would be greater than or similar to 3M(Moon).

  • 29. Cataldi, Gianni
    et al.
    Wu, Yanqin
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ohashi, Nagayoshi
    Moór, Attila
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ábrahám, Péter
    Asensio-Torres, Ruben
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Cavallius, Maria
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Dent, William R. F.
    Grady, Carol
    Henning, Thomas
    Higuchi, Aya E.
    Hughes, A. Meredith
    Janson, Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Kamp, Inga
    Kóspál, Ágnes
    Redfield, Seth
    Roberge, Aki
    Weinberger, Alycia
    Welsh, Barry
    The Surprisingly Low Carbon Mass in the Debris Disk around HD 322972020Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 892, nr 2, artikel-id 99Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Gas has been detected in a number of debris disks. It is likely secondary, i.e., produced by colliding solids. Here, we report ALMA Band 8 observations of neutral carbon in the CO-rich debris disk around the 15-30 Myr old A-type star HD 32297. We find that C-0 is located in a ring at similar to 110 au with an FWHM of similar to 80 au and has a mass of (3.5 0.2) x 10(-3) M-circle plus. Naively, such a surprisingly small mass can be accumulated from CO photodissociation in a time as short as similar to 10(4) yr. We develop a simple model for gas production and destruction in this system, properly accounting for CO self-shielding and shielding by neutral carbon, and introducing a removal mechanism for carbon gas. We find that the most likely scenario to explain both C-0 and CO observations is one where the carbon gas is rapidly removed on a timescale of order a thousand years and the system maintains a very high CO production rate of similar to 15 M-circle plus Myr(-1), much higher than the rate of dust grind-down. We propose a possible scenario to meet these peculiar conditions: the capture of carbon onto dust grains, followed by rapid CO re-formation and rerelease. In steady state, CO would continuously be recycled, producing a CO-rich gas ring that shows no appreciable spreading over time. This picture might be extended to explain other gas-rich debris disks.

  • 30.
    Cavallius, Maria
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Cataldi, Gianni
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Hungarian Academy of Sciences, Hungary; National Astronomical Observatory of Japan, Japan; University of Toronto, Canada.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Larsson, Bengt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Liseau, R.
    Upper limits on the water vapour content of the β Pictoris debris disk2019Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 628, artikel-id A127Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The debris disk surrounding β Pictoris has been observed with ALMA to contain a belt of CO gas with a distinct peak at ~85 au. This CO clump is thought to be the result of a region of enhanced density of solids that collide and release CO through vaporisation. The parent bodies are thought to be comparable to solar system comets, in which CO is trapped inside a water ice matrix

    Aims. Since H2O should be released along with CO, we aim to put an upper limit on the H2O gas mass in the disk of β Pictoris.

    Methods. We used archival data from the Heterodyne Instrument for the Far-Infrared (HIFI) aboard the Herschel Space Observatory to study the ortho-H2O 1(10)-1(01) emission line. The line is undetected. Using a python implementation of the radiative transfer code RADEX, we converted upper limits on the line flux to H2O gas masses. The resulting lower limits on the CO/H2O mass ratio are compared to the composition of solar system comets.

    Results. Depending on the assumed gas spatial distribution, we find a 95% upper limit on the ortho-H2O line flux of7.5×10−20W m−2or1.2×10−19W m−2. These translate into an upper limit on the H2O mass of7.4×1016–1.1×1018kg depending on both the electron density and gas kinetic temperature. The range of derived gas-phase CO/H2O ratios is marginally consistent with low-ratio solar system comets.

  • 31. Cernicharo, J.
    et al.
    Decin, L.
    Barlow, M. J.
    Agundez, M.
    Royer, P.
    Vandenbussche, B.
    Wesson, R.
    Polehampton, E. T.
    De Beck, E.
    Blommaert, J. A. D. L.
    Daniel, F.
    De Meester, W.
    Exter, K. M.
    Feuchtgruber, H.
    Gear, W. K.
    Goicoechea, J. R.
    Gomez, H. L.
    Groenewegen, M. A. T.
    Hargrave, P. C.
    Huygen, R.
    Imhof, P.
    Ivison, R. J.
    Jean, C.
    Kerschbaum, F.
    Leeks, S. J.
    Lim, T. L.
    Matsuura, M.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Posch, T.
    Regibo, S.
    Savini, G.
    Sibthorpe, B.
    Swinyard, B. M.
    Waelkens, C.
    Detection of anhydrous hydrochloric acid, HCl, in IRC+10216 with the Herschel SPIRE and PACS spectrometers Detection of HCI in IRC+102162010Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, s. L136-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on the detection of anhydrous hydrochloric acid (hydrogen chlorine, HCl) in the carbon-rich star IRC+10216 using the spectroscopic facilities onboard the Herschel satellite. Lines from J = 1-0 up to J = 7-6 have been detected. From the observed intensities, we conclude that HCl is produced in the innermost layers of the circumstellar envelope with an abundance relative to H-2 of 5 x 10(-8) and extends until the molecules reach its photodissociation zone. Upper limits to the column densities of AlH, MgH, CaH, CuH, KH, NaH, FeH, and other diatomic hydrides have also been obtained.

  • 32. Chauvin, M.
    et al.
    Florén, Hans-Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Jackson, M.
    Kamae, T.
    Kawano, T.
    Kiss, M.
    Kole, M.
    Mikhalev, V.
    Moretti, E.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Rydström, S.
    Takahashi, H.
    Iyudin, A.
    Arimoto, M.
    Fukazawa, Y.
    Kataoka, J.
    Kawai, N.
    Mizuno, T.
    Ryde, F.
    Tajima, H.
    Takahashi, T.
    Pearce, M.
    Observation of polarized hard X-ray emission from the Crab by the PoGOLite Pathfinder2016Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 456, nr 1, s. l84-L88Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have measured the linear polarization of hard X-ray emission from the Crab in a previously unexplored energy interval, 20-120 keV. The introduction of two new observational parameters, the polarization fraction and angle stands to disentangle geometrical and physical effects, thereby providing information on the pulsar wind geometry and magnetic field environment. Measurements are conducted using the PoGOLite Pathfinder - a balloon-borne polarimeter. Polarization is determined by measuring the azimuthal Compton scattering angle of incident X-rays in an array of plastic scintillators housed in an anticoincidence well. The polarimetric response has been characterized prior to flight using both polarized and unpolarized calibration sources. We address possible systematic effects through observations of a background field. The measured polarization fraction for the integrated Crab light curve is 18.4(-10.6)(+9.8) per cent, corresponding to an upper limit (99 per cent credibility) of 42.4 per cent, for a polarization angle of (149.2 +/- 16.0)degrees.

  • 33. Chauvin, M.
    et al.
    Florén, Hans-Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Jackson, M.
    Kamae, T.
    Kawano, T.
    Kiss, M.
    Kole, M.
    Mikhalev, V.
    Moretti, E.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Rydström, S.
    Takahashi, H.
    Lind, J.
    Strömberg, J. -E.
    Welin, O.
    Iyudin, A.
    Shifrin, D.
    Pearce, M.
    The design and flight performance of the PoGOLite Pathfinder balloon-borne hard X-ray polarimeter2016Ingår i: Experimental astronomy, ISSN 0922-6435, E-ISSN 1572-9508, Vol. 41, nr 1, s. 17-41Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the 50 years since the advent of X-ray astronomy there have been many scientific advances due to the development of new experimental techniques for detecting and characterising X-rays. Observations of X-ray polarisation have, however, not undergone a similar development. This is a shortcoming since a plethora of open questions related to the nature of X-ray sources could be resolved through measurements of the linear polarisation of emitted X-rays. The PoGOLite Pathfinder is a balloon-borne hard X-ray polarimeter operating in the 25-240 keV energy band from a stabilised observation platform. Polarisation is determined using coincident energy deposits in a segmented array of plastic scintillators surrounded by a BGO anticoincidence system and a polyethylene neutron shield. The PoGOLite Pathfinder was launched from the SSC Esrange Space Centre in July 2013. A near-circumpolar flight was achieved with a duration of approximately two weeks. The flight performance of the Pathfinder design is discussed for the three Crab observations conducted. The signal-to-background ratio for the observations is shown to be 0.25 +/- 0.03 and the Minimum Detectable Polarisation (99 % C.L.) is (28.4 +/- 2.2) %. A strategy for the continuation of the PoGOLite programme is outlined based on experience gained during the 2013 maiden flight.

  • 34. Clayton, Geoffrey C.
    et al.
    Sugerman, Ben E. K.
    Stanford, S. Adam
    Whitney, B. A.
    Honor, J.
    Babler, B.
    Barlow, M. J.
    Gordon, K. D.
    Andrews, J. E.
    Geballe, T. R.
    Bond, Howard E.
    De Marco, O.
    Lawson, W. A.
    Sibthorpe, B.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Polehampton, E.
    Gomez, H. L.
    Matsuura, M.
    Hargrave, P. C.
    Ivison, R. J.
    Wesson, R.
    Leeks, S. J.
    Swinyard, B. M.
    Lim, T. L.
    THE CIRCUMSTELLAR ENVIRONMENT OF R CORONAE BOREALIS: WHITE DWARF MERGER OR FINAL-HELIUM-SHELL FLASH?2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 743, nr 1, s. 44-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In 2007, R Coronae Borealis (R CrB) went into a historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 mu m with Gemini/GMOS, Hubble Space Telescope/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around R CrB are cometary globules caused by wind from the star streaming past dense blobs. The estimated dust mass of the knots is consistent with their being responsible for the R CrB declines if they form along the line of sight to the star. In addition, there is a large diffuse shell extending up to 4 pc away from the star containing cool 25 K dust that is detected all the way out to 500 mu m. The spectral energy distribution of R CrB can be well fitted by a 150 AU disk surrounded by a very large diffuse envelope which corresponds to the size of the observed nebulosity. The total masses of the disk and envelope are 10(-4) and 2M(circle dot), respectively, assuming a gas-to-dust ratio of 100. The evidence pointing toward a white dwarf merger or a final-helium-shell flash origin for R CrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that R CrB shows significant lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of R CrB and its high fluorine abundance support a white dwarf merger.

  • 35. Covino, S.
    et al.
    Andra, 14
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Andra, 39
    The complex light curve of the afterglow of GRB071010A2008Ingår i: Monthly Notices of the Royal Astronomical Society, Vol. 388, nr 1, s. 347-356Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present and discuss the results of an extensive observational campaign devoted to GRB071010A, a long-duration gamma-ray burst detected by the Swift satellite. This event was followed for almost a month in the optical/near-infrared (NIR) with various telescopes starting from about 2min after the high-energy event. Swift XRT observations started only later at about 0.4d. The light-curve evolution allows us to single out an initial rising phase with a maximum at about 7min, possibly the afterglow onset in the context of the standard fireball model, which is then followed by a smooth decay interrupted by a sharp rebrightening at about 0.6d. The rebrightening was visible in both the optical/NIR and X-rays and can be interpreted as an episode of discrete energy injection, although various alternatives are possible. A steepening of the afterglow light curve is recorded at about 1d. The entire evolution of the optical/NIR afterglow is consistent with being achromatic. This could be one of the few identified GRB afterglows with an achromatic break in the X-ray through the optical/NIR bands. Polarimetry was also obtained at about 1d, just after the rebrightening and almost coincident with the steepening. This provided a fairly tight upper limit of 0.9 per cent for the polarized-flux fraction.

  • 36. Danilovich, T.
    et al.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Black, J. H.
    Justtanont, K.
    Olofsson, H.
    Classifying the secondary component of the binary star W Aquilae2015Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 574, artikel-id A23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims. The object W Aql is an asymptotic giant branch (AGB) star with a faint companion. By determining more carefully the properties of the companion, we hope to better constrain the properties of the AGB star. Methods. We present new spectral observations of the binary star W Aql at minimum and maximum brightness and new photometric observations of W Aql at minimum brightness. Results. The composite spectrum near minimum light is predominantly from the companion at wavelengths lambda 6000 angstrom. This spectrum can be classified as F8 to G0, and the brightness of the companion is that of a dwarf star. Therefore, it can be concluded that the companion is a main sequence star. From this, we are able to constrain the mass of the AGB component to 1.04-3 M-circle dot and the mass of the W Aql system to 2.1-4.1 M-circle dot. Our photometric results are broadly consistent with this classification and suggest that the main sequence component suffers from approximately 2 mag of extinction in the V band primarily due to the dust surrounding the AGB component.

  • 37. de Vries, B. L.
    et al.
    Acke, B.
    Blommaert, J. A. D. L.
    Waelkens, C.
    Waters, L. B. F. M.
    Vandenbussche, B.
    Min, M.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Dominik, C.
    Decin, L.
    Barlow, M. J.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Di Francesco, J.
    Glauser, A. M.
    Greaves, J.
    Harvey, P. M.
    Holland, W. S.
    Ivison, R. J.
    Liseau, R.
    Pantin, E. E.
    Pilbratt, G. L.
    Royer, P.
    Sibthorpe, B.
    Comet-like mineralogy of olivine crystals in an extrasolar proto-Kuiper belt2012Ingår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 490, nr 7418, s. 74-76Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Some planetary systems harbour debris disks containing planetesimals such as asteroids and comets(1). Collisions between such bodies produce small dust particles(2), the spectral features of which reveal their composition and, hence, that of their parent bodies. A measurement of the composition of olivine crystals (Mg2-2xFe2xSiO4) has been done for the protoplanetary disk HD 100546 (refs 3, 4) and for olivine crystals in the warm inner parts of planetary systems. The latter compares well with the iron-rich olivine in asteroids(5,6) (x approximate to 0.29). In the cold outskirts of the beta Pictoris system, an analogue to the young Solar System, olivine crystals were detected(7) but their composition remained undetermined, leaving unknown how the composition of the bulk of Solar System cometary olivine grains compares with that of extrasolar comets(8,9). Here we report the detection of the 69-micrometre-wavelength band of olivine crystals in the spectrum of beta Pictoris. Because the disk is optically thin, we can associate the crystals with an extrasolar proto-Kuiper belt a distance of 15-45 astronomical units from the star (one astronomical unit is the Sun-Earth distance), determine their magnesium-rich composition (x = 0.01 +/- 0.001) and show that they make up 3.6 +/- 1.0 per cent of the total dust mass. These values are strikingly similar to those for the dust emitted by the most primitive comets in the Solar System(8-10), even though beta Pictoris is more massive and more luminous and has a different planetary system architecture.

  • 38. Decin, L.
    et al.
    Agundez, M.
    Barlow, M. J.
    Daniel, F.
    Cernicharo, J.
    Lombaert, R.
    De Beck, E.
    Royer, P.
    Vandenbussche, B.
    Wesson, R.
    Polehampton, E. T.
    Blommaert, J. A. D. L.
    De Meester, W.
    Exter, K.
    Feuchtgruber, H.
    Gear, W. K.
    Gomez, H. L.
    Groenewegen, M. A. T.
    Guelin, M.
    Hargrave, P. C.
    Huygen, R.
    Imhof, P.
    Ivison, R. J.
    Jean, C.
    Kahane, C.
    Kerschbaum, F.
    Leeks, S. J.
    Lim, T.
    Matsuura, M.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Posch, T.
    Regibo, S.
    Savini, G.
    Sibthorpe, B.
    Swinyard, B. M.
    Yates, J. A.
    Waelkens, C.
    Warm water vapour in the sooty outflow from a luminous carbon star2010Ingår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 467, nr 7311, s. 64-67Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The detection(1) of circumstellar water vapour around the ageing carbon star IRC + 10216 challenged the current understanding of chemistry in old stars, because water was predicted(2) to be almost absent in carbon-rich stars. Several explanations for the water were postulated, including the vaporization of icy bodies (comets or dwarf planets) in orbit around the star(1), grain surface reactions(3), and photochemistry in the outer circumstellar envelope(4). With a single water line detected so far from this one carbon-rich evolved star, it is difficult to discriminate between the different mechanisms proposed. Here we report the detection of dozens of water vapour lines in the far-infrared and sub-millimetre spectrum of IRC + 10216 using the Herschel satellite(5). This includes some high-excitation lines with energies corresponding to similar to 1,000 K, which can be explained only if water is present in the warm inner sooty region of the envelope. A plausible explanation for the warm water appears to be the penetration of ultraviolet photons deep into a clumpy circumstellar envelope. This mechanism also triggers the formation of other molecules, such as ammonia, whose observed abundances(6) are much higher than hitherto predicted(7).

  • 39. Decin, L.
    et al.
    Cernicharo, J.
    Barlow, M. J.
    Royer, P.
    Vandenbussche, B.
    Wesson, R.
    Polehampton, E. T.
    De Beck, E.
    Agundez, M.
    Blommaert, J. A. D. L.
    Cohen, M.
    Daniel, F.
    De Meester, W.
    Exter, K.
    Feuchtgruber, H.
    Fonfria, J. P.
    Gear, W. K.
    Goicoechea, J. R.
    Gomez, H. L.
    Groenewegen, M. A. T.
    Hargrave, P. C.
    Huygen, R.
    Imhof, P.
    Ivison, R. J.
    Jean, C.
    Kerschbaum, F.
    Leeks, S. J.
    Lim, T.
    Matsuura, M.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Posch, T.
    Regibo, S.
    Savini, G.
    Sibthorpe, B.
    Swinyard, B. M.
    Tercero, B.
    Waelkens, C.
    Witherick, D. K.
    Yates, J. A.
    Silicon in the dust formation zone of IRC+102162010Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, s. L143-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interstellar medium is enriched primarily by matter ejected from evolved low and intermediate mass stars. The outflows from these stars create a circumstellar envelope in which a rich gas-phase and dust-nucleation chemistry takes place. We observed the nearest carbon-rich evolved star, IRC + 10216, using the PACS (55-210 mu m) and SPIRE (194-672 mu m) spectrometers on board Herschel. We find several tens of lines from SiS and SiO, including lines from the v = 1 vibrational level. For SiS these transitions range up to J = 124-123, corresponding to energies around 6700 K, while the highest detectable transition is J = 90-89 for SiO, which corresponds to an energy around 8400 K. Both species trace the dust formation zone of IRC + 10216, and the broad energy ranges involved in their detected transitions permit us to derive the physical properties of the gas and the particular zone in which each species has been formed. This allows us to check the accuracy of chemical thermodynamical equilibrium models and the suggested depletion of SiS and SiO due to accretion onto dust grains.

  • 40. Deline, A.
    et al.
    Hooton, M. J.
    Lendl, M.
    Morris, B.
    Salmon, S.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Broeg, C.
    Ehrenreich, D.
    Beck, M.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Hoyer, S.
    Sulis, S.
    Van Grootel, V.
    Bourrier, V.
    Demangeon, O.
    Demory, B.-O.
    Heng, K.
    Parviainen, H.
    Serrano, L. M.
    Singh, V.
    Bonfanti, A.
    Fossati, L.
    Kitzmann, D.
    Sousa, S. G.
    Wilson, T. G.
    Alibert, Y.
    Alonso, R.
    Anglada, G.
    Bárczy, T.
    Barrado Navascues, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, T.
    Bekkelien, A.
    Benz, W.
    Billot, N.
    Bonfils, X.
    Cabrera, J.
    Charnoz, S.
    Collier Cameron, A.
    Corral van Damme, C.
    Csizmadia, Sz.
    Davies, M. B.
    Deleuil, M.
    Delrez, L.
    de Roche, T.
    Erikson, A.
    Fortier, A.
    Fridlund, M.
    Futyan, D.
    Gandolfi, D.
    Gillon, M.
    Güdel, M.
    Gutermann, P.
    Hasiba, J.
    Isaak, K. G.
    Kiss, L.
    Laskar, J.
    Lecavelier des Etangs, A.
    Lovis, C.
    Magrin, D.
    Maxted, P. F. L.
    Munari, M.
    Nascimbeni, V.
    Ottensamer, R.
    Pagano, I.
    Pallé, E.
    Peter, G.
    Piotto, G.
    Pollacco, D.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Rauer, H.
    Ribas, I.
    Santos, N. C.
    Scandariato, G.
    Ségransan, D.
    Simon, A. E.
    Smith, A. M. S.
    Steller, M.
    Szabó, Gy. M.
    Thomas, N.
    Udry, S.
    Walter, I.
    Walton, N.
    The atmosphere and architecture of WASP-189 b probed by its CHEOPS phase curve2022Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 659, artikel-id A74Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Gas giants orbiting close to hot and massive early-type stars can reach dayside temperatures that are comparable to thoseof the coldest stars. These ‘ultra-hot Jupiters’ have atmospheres made of ions and atomic species from molecular dissociation andfeature strong day-to-night temperature gradients. Photometric observations at different orbital phases provide insights on the planet’satmospheric properties.

    Aims. We aim to analyse the photometric observations of WASP-189 acquired with the Characterising Exoplanet Satellite (CHEOPS)to derive constraints on the system architecture and the planetary atmosphere.

    Methods. We implemented a light-curve model suited for an asymmetric transit shape caused by the gravity-darkened photosphere ofthe fast-rotating host star. We also modelled the reflective and thermal components of the planetary flux, the effect of stellar oblatenessand light-travel time on transit-eclipse timings, the stellar activity, and CHEOPS systematics.

    Results. From the asymmetric transit, we measure the size of the ultra-hot Jupiter WASP-189 b, Rp = 1.600+0.017−0.016 RJ, with a precisionof 1%, and the true orbital obliquity of the planetary system, Ψp = 89.6 ± 1.2 deg (polar orbit). We detect no significant hotspot offsetfrom the phase curve and obtain an eclipse depth of δecl = 96.5+4.5−5.0ppm, from which we derive an upper limit on the geometric albedo:Ag < 0.48. We also find that the eclipse depth can only be explained by thermal emission alone in the case of extremely inefficientenergy redistribution. Finally, we attribute the photometric variability to the stellar rotation, either through superficial inhomogeneitiesor resonance couplings between the convective core and the radiative envelope.

    Conclusions. Based on the derived system architecture, we predict the eclipse depth in the upcoming Transiting Exoplanet SurveySatellite (TESS) observations to be up to ∼165 ppm. High-precision detection of the eclipse in both CHEOPS and TESS passbandsmight help disentangle reflective and thermal contributions. We also expect the right ascension of the ascending node of the orbit toprecess due to the perturbations induced by the stellar quadrupole moment J2 (oblateness).

  • 41. Demangeon, O. D. S.
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Walton, N. A.
    Asymmetry in the atmosphere of the ultra-hot Jupiter WASP-76 b2024Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 684, artikel-id A27Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. WASP-76 b has been a recurrent subject of study since the detection of a signature in high-resolution transit spectroscopy data indicating an asymmetry between the two limbs of the planet. The existence of this asymmetric signature has been confirmed by multiple studies, but its physical origin is still under debate. In addition, it contrasts with the absence of asymmetry reported in the infrared (IR) phase curve.

    Aims. We provide a more comprehensive dataset of WASP-76 b with the goal of drawing a complete view of the physical processes at work in this atmosphere. In particular, we attempt to reconcile visible high-resolution transit spectroscopy data and IR broadband phase curves.

    Methods. We gathered 3 phase curves, 20 occultations, and 6 transits for WASP-76 b in the visible with the CHEOPS space telescope. We also report the analysis of three unpublished sectors observed by the TESS space telescope (also in the visible), which represents 34 phase curves.

    Results. WASP-76 b displays an occultation of 260 ± 11 and 152 ± 10 ppm in TESS and CHEOPS bandpasses respectively. Depending on the composition assumed for the atmosphere and the data reduction used for the IR data, we derived geometric albedo estimates that range from 0.05 ± 0.023 to 0.146 ± 0.013 and from <0.13 to 0.189 ± 0.017 in the CHEOPS and TESS bandpasses, respectively. As expected from the IR phase curves, a low-order model of the phase curves does not yield any detectable asymmetry in the visible either. However, an empirical model allowing for sharper phase curve variations offers a hint of a flux excess before the occultation, with an amplitude of ~40 ppm, an orbital offset of ~ −30°, and a width of ~20º. We also constrained the orbital eccentricity of WASP-76 b to a value lower than 0.0067, with a 99.7% confidence level. This result contradicts earlier proposed scenarios aimed at explaining the asymmetry observed in high-resolution transit spectroscopy.

    Conclusions. In light of these findings, we hypothesise that WASP-76 b could have night-side clouds that extend predominantly towards its eastern limb. At this limb, the clouds would be associated with spherical droplets or spherically shaped aerosols of an unknown species, which would be responsible for a glory effect in the visible phase curves.

  • 42. Djupvik, A. A.
    et al.
    André, Philippe
    Bontemps, Sylvain
    Motte, F.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Gålfalk, Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Florén, Hans-Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    A multi-wavelength census of star formation activity in the young embedded cluster around Serpens/G3-G62006Ingår i: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 458, nr 3, s. 789-803Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims.The aim of this paper is to characterise the star formation activity in the poorly studied embedded cluster Serpens/G3-G6, located ~45 arcmin (3 pc) to the south of the Serpens Cloud Core, and to determine the luminosity and mass functions of its population of Young Stellar Objects (YSOs).

    Methods: .Multi-wavelength broadband photometry was obtained to sample the near and mid-IR spectral energy distributions to separate YSOs from field stars and classify the YSO evolutionary stage. ISOCAM mapping in the two filters LW2 (5-8.5 μm) and LW3 (12-18 μm) of a 19 arcmin × 16 arcmin field was combined with JHKS data from 2MASS, KS data from Arnica/NOT, and L arcmin data from SIRCA/NOT. Continuum emission at 1.3 mm (IRAM) and 3.6 cm (VLA) was mapped to study the cloud structure and the coldest/youngest sources. Deep narrow band imaging at the 2.12 μm S(1) line of H2 from NOTCam/NOT was obtained to search for signs of bipolar outflows.

    Results: .We have strong evidence for a stellar population of 31 Class II sources, 5 flat-spectrum sources, 5 Class I sources, and two Class 0 sources. Our method does not sample the Class III sources. The cloud is composed of two main dense clumps aligned along a ridge over ~0.5 pc plus a starless core coinciding with absorption features seen in the ISOCAM maps. We find two S-shaped bipolar collimated flows embedded in the NE clump, and propose the two driving sources to be a Class 0 candidate (MMS3) and a double Class I (MMS2). For the Class II population we find a best age of ~2 Myr and compatibility with recent Initial Mass Functions (IMFs) by comparing the observed Class II luminosity function (LF), which is complete to 0.08 Lȯ, to various model LFs with different star formation scenarios and input IMFs.

  • 43. Dyrek, Achrène
    et al.
    Min, Michiel
    Decin, Leen
    Bouwman, Jeroen
    Crouzet, Nicolas
    Mollière, Paul
    Lagage, Pierre-Olivier
    Konings, Thomas
    Tremblin, Pascal
    Güdel, Manuel
    Pye, John
    Waters, Rens
    Henning, Thomas
    Vandenbussche, Bart
    Martinez, Francisco Ardevol
    Argyriou, Ioannis
    Ducrot, Elsa
    Heinke, Linus
    van Looveren, Gwenael
    Absil, Olivier
    Barrado, David
    Baudoz, Pierre
    Boccaletti, Anthony
    Cossou, Christophe
    Coulais, Alain
    Edwards, Billy
    Gastaud, René
    Glasse, Alistair
    Glauser, Adrian
    Greene, Thomas P.
    Kendrew, Sarah
    Krause, Oliver
    Lahuis, Fred
    Mueller, Michael
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Patapis, Polychronis
    Rouan, Daniel
    Royer, Pierre
    Scheithauer, Silvia
    Waldmann, Ingo
    Whiteford, Niall
    Colina, Luis
    van Dishoeck, Ewine F.
    Östlin, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Ray, Tom P.
    Wright, Gillian
    SO2, silicate clouds, but no CH4 detected in a warm Neptune2024Ingår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 625, s. 51-54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    WASP-107b is a warm (approximately 740 K) transiting planet with a Neptune-like mass of roughly 30.5 M and Jupiter-like radius of about 0.94 RJ (refs. 1,2), whose extended atmosphere is eroding3. Previous observations showed evidence for water vapour and a thick, high-altitude condensate layer in the atmosphere of WASP-107b (refs. 4,5). Recently, photochemically produced sulfur dioxide (SO2) was detected in the atmosphere of a hot (about 1,200 K) Saturn-mass planet from transmission spectroscopy near 4.05 μm (refs. 6,7), but for temperatures below about 1,000 K, sulfur is predicted to preferably form sulfur allotropes instead of SO2 (refs. 8,9,10). Here we report the 9σ detection of two fundamental vibration bands of SO2, at 7.35 μm and 8.69 μm, in the transmission spectrum of WASP-107b using the Mid-Infrared Instrument (MIRI) of JWST. This discovery establishes WASP-107b as the second irradiated exoplanet with confirmed photochemistry, extending the temperature range of exoplanets exhibiting detected photochemistry from about 1,200 K down to about 740 K. Furthermore, our spectral analysis reveals the presence of silicate clouds, which are strongly favoured (around 7σ) over simpler cloud set-ups. Furthermore, water is detected (around 12σ) but methane is not. These findings provide evidence of disequilibrium chemistry and indicate a dynamically active atmosphere with a super-solar metallicity.

  • 44. Ehrenreich, D.
    et al.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Florén, Hans Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Walton, N. A.
    A full transit of v2 Lupi d and the search for an exomoon in its Hill sphere with CHEOPS2023Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 671, artikel-id A154Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The planetary system around the naked-eye star v2 Lupi (HD 136352; TOI-2011) is composed of three exoplanets with masses of 4.7, 11.2, and 8.6 Earth masses (M). The TESS and CHEOPS missions revealed that all three planets are transiting and have radii straddling the radius gap separating volatile-rich and volatile-poor super-earths. Only a partial transit of planet d had been covered so we re-observed an inferior conjunction of the long-period 8.6 M exoplanet v2 Lup d with the CHEOPS space telescope. We confirmed its transiting nature by covering its whole 9.1 h transit for the first time. We refined the planet transit ephemeris to P = 107.1361−0.0022+0.0019 days and Tc = 2459009.7759−0.0096+0.0101 BJDTDB, improving by ~40 times on the previously reported transit timing uncertainty. This refined ephemeris will enable further follow-up of this outstanding long-period transiting planet to search for atmospheric signatures or explore the planet’s Hill sphere in search for an exomoon. In fact, the CHEOPS observations also cover the transit of a large fraction of the planet’s Hill sphere, which is as large as the Earth’s, opening the tantalising possibility of catching transiting exomoons. We conducted a search for exomoon signals in this single-epoch light curve but found no conclusive photometric signature of additional transiting bodies larger than Mars. Yet, only a sustained follow-up of v2 Lup d transits will warrant a comprehensive search for a moon around this outstanding exoplanet.

  • 45. Eiroa, C.
    et al.
    Fedele, D.
    Maldonado, J.
    Gonzalez-Garcia, B. M.
    Rodmann, J.
    Heras, A. M.
    Pilbratt, G. L.
    Augereau, J. -Ch.
    Mora, A.
    Montesinos, B.
    Ardila, D.
    Bryden, G.
    Liseau, R.
    Stapelfeldt, K.
    Launhardt, R.
    Solano, E.
    Bayo, A.
    Absil, O.
    Arevalo, M.
    Barrado, D.
    Beichmann, C.
    Danchi, W.
    del Burgo, C.
    Ertel, S.
    Fridlund, M.
    Fukagawa, M.
    Gutierrez, R.
    Gruen, E.
    Kamp, I.
    Krivov, A.
    Lebreton, J.
    Loehne, T.
    Lorente, R.
    Marshall, J.
    Martinez-Arnaiz, R.
    Meeus, G.
    Montes, D.
    Morbidelli, A.
    Mueller, S.
    Mutschke, H.
    Nakagawa, T.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ribas, I.
    Roberge, A.
    Sanz-Forcada, J.
    Thebault, P.
    Walker, H.
    White, G. J.
    Wolf, S.
    Cold DUst around NEarby Stars (DUNES). First results A resolved exo-Kuiper belt around the solar-like star zeta(2) Ret2010Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, s. L131-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the first far-IR observations of the solar-type stars delta Pav, HR 8501, 51 Peg and zeta(2) Ret, taken within the context of the DUNES Herschel open time key programme (OTKP). This project uses the PACS and SPIRE instruments with the objective of studying infrared excesses due to exo-Kuiper belts around nearby solar-type stars. The observed 100 mu m fluxes from delta Pav, HR 8501, and 51 Peg agree with the predicted photospheric fluxes, excluding debris disks brighter than L-dust/L-star similar to 5 x 10(-7) (1 sigma level) around those stars. A flattened, disk-like structure with a semi-major axis of similar to 100 AU in size is detected around zeta(2) Ret. The resolved structure suggests the presence of an eccentric dust ring, which we interpret as an exo-Kuiper belt with L-dust/L-star approximate to 10(-5).

  • 46.
    Florén, Hans Gustav Axel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    A CHEOPS-enhanced view of the HD 3167 system2022Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 668, artikel-id A31Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Much remains to be understood about the nature of exoplanets smaller than Neptune, most of which have been discovered in compact multi-planet systems. With its inner ultra-short period planet b aligned with the star and two larger outer planets d-c on polar orbits, the multi-planet system HD 3167 features a peculiar architecture and offers the possibility to investigate both dynamical and atmospheric evolution processes. To this purpose we combined multiple datasets of transit photometry and radial velocimetry (RV) to revise the properties of the system and inform models of its planets. This effort was spearheaded by CHEOPS observations of HD 3167b, which appear inconsistent with a purely rocky composition despite its extreme irradiation. Overall the precision on the planetary orbital periods are improved by an order of magnitude, and the uncertainties on the densities of the transiting planets b and c are decreased by a factor of 3. Internal structure and atmospheric simulations draw a contrasting picture between HD 3167d, likely a rocky super-Earth that lost its atmosphere through photo-evaporation, and HD 3167c, a mini-Neptune that kept a substantial primordial gaseous envelope. We detect a fourth, more massive planet on a larger orbit, likely coplanar with HD 3167d-c. Dynamical simulations indeed show that the outer planetary system d-c-e was tilted, as a whole, early in the system history, when HD 3167b was still dominated by the star influence and maintained its aligned orbit. RV data and direct imaging rule out that the companion that could be responsible for the present-day architecture is still bound to the HD 3167 system. Similar global studies of multi-planet systems will tell how many share the peculiar properties of the HD 3167 system, which remains a target of choice for follow-up observations and simulations.

  • 47.
    Florén, Hans Gustav Axel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Characterization of the HD 108236 system with CHEOPS and TESS Confirmation of a fifth transiting planet2022Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 668, artikel-id A117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. The HD 108236 system was first announced with the detection of four small planets based on TESS data. Shortly after, the transit of an additional planet with a period of 29.54 d was serendipitously detected by CHEOPS. In this way, HD 108236 (V = 9.2) became one of the brightest stars known to host five small transiting planets (Rp < 3 R).

    Aims. We characterize the planetary system by using all the data available from CHEOPS and TESS space missions. We use the flexible pointing capabilities of CHEOPS to follow up the transits of all the planets in the system, including the fifth transiting body.

    Methods. After updating the host star parameters by using the results from Gaia eDR3, we analyzed 16 and 43 transits observed by CHEOPS and TESS, respectively, to derive the planets’ physical and orbital parameters. We carried out a timing analysis of the transits of each of the planets of HD 108236 to search for the presence of transit timing variations.

    Results. We derived improved values for the radius and mass of the host star (R = 0.876 ± 0.007 R0 and M = 0.867-0.046+0.047M⊙). We confirm the presence of the fifth transiting planet f in a 29.54 d orbit. Thus, the HD 108236 system consists of five planets of Rb = 1.587±0.028, Rc = 2.122±0.025, Rd = 2.629 ± 0.031, Re = 3.008 ± 0.032, and Rf = 1.89 ± 0.04 [R]. We refine the transit ephemeris for each planet and find no significant transit timing variations for planets c, d, and e. For planets b and f, instead, we measure significant deviations on their transit times (up to 22 and 28 min, respectively) with a non-negligible dispersion of 9.6 and 12.6 min in their time residuals.

    Conclusions. We confirm the presence of planet f and find no significant evidence for a potential transiting planet in a 10.9 d orbital period, as previously suggested. Further monitoring of the transits, particularly for planets b and f, would confirm the presence of the observed transit time variations. HD 108236 thus becomes a key multi-planetary system for the study of formation and evolution processes. The reported precise results on the planetary radii – together with a profuse RV monitoring – will allow for an accurate characterization of the internal structure of these planets.

  • 48.
    Florén, Hans Gustav Axel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Discovery of TOI-1260d and the characterization of the multiplanet system2023Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 519, nr 1, s. 1437-1451Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the discovery of a third planet transiting the star TOI-1260, previously known to host two transiting sub-Neptune planets with orbital periods of 3.127 and 7.493 d, respectively. The nature of the third transiting planet with a 16.6-d orbit is supported by ground-based follow-up observations, including time-series photometry, high-angular resolution images, spectroscopy, and archival imagery. Precise photometric monitoring with CHEOPS allows to improve the constraints on the parameters of the system, improving our knowledge on their composition. The improved radii of TOI-1260b and TOI-1260c are 2.36±0.06R⊕2.36±0.06R⊕⁠, 2.82±0.08R⊕2.82±0.08R⊕⁠, respectively while the newly discovered third planet has a radius of 3.09±0.09R⊕3.09±0.09R⊕⁠. The radius uncertainties are in the range of 3 per cent, allowing a precise interpretation of the interior structure of the three planets. Our planet interior composition model suggests that all three planets in the TOI-1260 system contains some fraction of gas. The innermost planet TOI-1260b has most likely lost all of its primordial hydrogen-dominated envelope. Planets c and d were also likely to have experienced significant loss of atmospheric through escape, but to a lesser extent compared to planet b.

  • 49.
    Florén, Hans Gustav Axel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Examining the orbital decay targets KELT-9 b, KELT-16 b, and WASP-4 b, and the transit-timing variations of HD 97658 b2023Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 669, artikel-id A124Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Tidal orbital decay is suspected to occur for hot Jupiters in particular, with the only observationally confirmed case of this being WASP-12b. By examining this effect, information on the properties of the host star can be obtained using the so-called stellar modified tidal quality factor Q*, which describes the efficiency with which the kinetic energy of the planet is dissipated within the star. This can provide information about the interior of the star.

    Aims. In this study, we aim to improve constraints on the tidal decay of the KELT-9, KELT-16, and WASP-4 systems in order to find evidence for or against the presence of tidal orbital decay. With this, we want to constrain the Q* value for each star. In addition, we aim to test the existence of the transit timing variations (TTVs) in the HD 97658 system, which previously favoured a quadratic trend with increasing orbital period.

    Methods. Making use of newly acquired photometric observations from CHEOPS (CHaracterising ExOplanet Satellite) and TESS (Transiting Exoplanet Survey Satellite), combined with archival transit and occultation data, we use Markov chain Monte Carlo (MCMC) algorithms to fit three models to the data, namely a constant-period model, an orbital-decay model, and an apsidal-precession model.

    Results. We find that the KELT-9 system is best described by an apsidal-precession model for now, with an orbital decay trend at over 2 σ being a possible solution as well. A Keplerian orbit model with a constant orbital period provides the best fit to the transit timings of KELT-16 b because of the scatter and scale of their error bars. The WASP-4 system is best represented by an orbital decay model at a 5 σ significance, although apsidal precession cannot be ruled out with the present data. For HD 97658 b, using recently acquired transit observations, we find no conclusive evidence for a previously suspected strong quadratic trend in the data.

  • 50. Fridlund, M.
    et al.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Florén, Hans Gustav Axel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Walton, N. A.
    Planets observed with CHEOPS: Two super-Earths orbiting the red dwarf star TOI-7762024Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 684, artikel-id A12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. M-dwarf stars are the most common of potential exoplanet host stars in the Galaxy. It is therefore very important to understand planetary systems orbiting such stars and to determine the physical parameters of such planets with high precision. Also with the launch of the James Webb Space Telescope (JWST) the observation of atmospheric parameters of planets orbiting these stars has begun. It is therefore required to determine properties of potential targets.

    Aims. Two planets around the red dwarf TOI-776 were detected by TESS. The objective of our study was to use transit observations obtained by the CHEOPS space mission to improve the current precision of the planetary radii, as well as additional radial velocity (RV) data in order to improve mass estimates of the two planets. Using these quantities, we wanted to derive the bulk densities of those planets, improving the precision in earlier results, and use this information to put them in context of other exoplanetary systems involving very low mass stars.

    Methods. Utilizing new transit data from the CHEOPS satellite and its photometric telescope, we obtained very high precision planetary transit measurements. Interpretation of these provides updated planetary radii, along with other system parameters. A concurrent ESO large observing program using the high precision spectrograph HARPS has doubled the available radial velocity data. Calculating the power spectrum of a number of stellar activity indices we update the previously estimated stellar rotation period to a lower value.

    Results. The CHEOPS data provide precise transit depths of 909 and 1177 ppm translating into radii of Rb = R and Rc = R, respectively. Our interpretation of the radial velocities and activity indicator time series data estimates a stellar rotation period for this early M dwarf of ~21.1 days. A further multi-dimensional Gaussian process approach confirm this new estimate. By performing a Skew-Normal (SN) fit onto the Cross Correlation Functions we extracted the RV data and the activity indicators to estimate the planetary masses, obtaining Mb = M and Mc = M.

    Conclusions. We improve the precision in planetary radius for TOI-776 b and c by a factor of more than two. Our data and modelling give us parameters of both bodies consistent with mini-Neptunes, albeit with a relatively high density. The stellar activity of TOI-776 is found to have increased by a factor larger than 2 since the last set of observations.

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