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  • 101. Scholz, Alexander
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Rotation and Activity of Pre-Main-Sequence Stars2007Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, The Astrophysical JournalArtikkel i tidsskrift (Fagfellevurdert)
  • 102. Sebastian, D
    et al.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Walton, N A
    The EBLM project - IX: Five fully convective M-dwarfs, precisely measured with CHEOPS and TESS light curves2023Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 519, nr 3, s. 3546-3563Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Eclipsing binaries are important benchmark objects to test and calibrate stellar structure and evolution models. This is especially true for binaries with a fully convective M-dwarf component for which direct measurements of these stars' masses and radii are difficult using other techniques. Within the potential of M-dwarfs to be exoplanet host stars, the accuracy of theoretical predictions of their radius and effective temperature as a function of their mass is an active topic of discussion. Not only the parameters of transiting exoplanets but also the success of future atmospheric characterization relies on accurate theoretical predictions. We present the analysis of five eclipsing binaries with low-mass stellar companions out of a subsample of 23, for which we obtained ultra-high-precision light curves using the CHEOPS satellite. The observation of their primary and secondary eclipses are combined with spectroscopic measurements to precisely model the primary parameters and derive the M-dwarfs mass, radius, surface gravity, and effective temperature estimates using the PYCHEOPS data analysis software. Combining these results to the same set of parameters derived from TESS light curves, we find very good agreement (better than 1 percent for radius and better than 0.2 percent for surface gravity). We also analyse the importance of precise orbits from radial velocity measurements and find them to be crucial to derive M-dwarf radii in a regime below 5 percent accuracy. These results add five valuable data points to the mass-radius diagram of fully convective M-dwarfs.

  • 103. Sibthorpe, B.
    et al.
    Vandenbussche, B.
    Greaves, J. S.
    Pantin, E.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Acke, B.
    Barlow, M. J.
    Blommaert, J. A. D. L.
    Bouwman, J.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Cohen, M.
    De Meester, W.
    Dent, W. R. F.
    Di Francesco, J.
    Dominik, C.
    Fridlund, M.
    Gear, W. K.
    Glauser, A. M.
    Gomez, H. L.
    Hargrave, P. C.
    Harvey, P. M.
    Henning, Th.
    Heras, A. M.
    Hogerheijde, M. R.
    Holland, W. S.
    Ivison, R. J.
    Leeks, S. J.
    Lim, T. L.
    Liseau, R.
    Matthews, B. C.
    Naylor, D. A.
    Pilbratt, G. L.
    Polehampton, E. T.
    Regibo, S.
    Royer, P.
    Sicilia-Aguilar, A.
    Swinyard, B. M.
    Waelkens, C.
    Walker, H. J.
    Wesson, R.
    The Vega debris disc: A view from Herschel2010Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, s. L130-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present five band imaging of the Vega debris disc obtained using the Herschel Space Observatory. These data span a wavelength range of 70-500 mu m with full-width half-maximum angular resolutions of 5.6-36.9 ''. The disc is well resolved in all bands, with the ring structure visible at 70 and 160 mu m. Radial profiles of the disc surface brightness are produced, and a disc radius of 11 '' (similar to 85AU) is determined. The disc is seen to have a smooth structure thoughout the entire wavelength range, suggesting that the disc is in a steady state, rather than being an ephemeral structure caused by the recent collision of two large planetesimals.

  • 104. Sicardy, B.
    et al.
    Brandeker, Alexis
    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.
    Kate, A.
    Constraints on the evolution of the Triton atmosphere from occultations: 1989-20222024Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 682, artikkel-id L24Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. In about 2000, the south pole of Triton experienced an extreme summer solstice that occurs every ∼650 years, when the subsolar latitude reached about 50°S. Bracketing this epoch, a few occultations probed the Triton atmosphere in 1989, 1995, 1997, 2008, and 2017. A recent ground-based stellar occultation observed on 6 October 2022 provides a new measurement of the atmospheric pressure on Triton. This is presented here.

    Aims. The goal is to constrain the volatile transport models (VTMs) of the Triton atmosphere. The atmosphere is basically in vapor pressure equilibrium with the nitrogen ice at its surface.

    Methods. Fits to the occultation light curves yield the atmospheric pressure of Triton at the reference radius 1400 km, from which the surface pressure is deduced.

    Results. The fits provide a pressure p1400 = 1.211 ± 0.039 μbar at radius 1400 km (47 km altitude), from which a surface pressure of psurf = 14.54 ± 0.47 μbar is deduced (1σ error bars). To within the error bars, this is identical to the pressure derived from the previous occultation of 5 October 2017, p1400 = 1.18 ± 0.03 μbar and psurf = 14.1 ± 0.4 μbar, respectively. Based on recent models of the volatile cycles of Triton, the overall evolution of the surface pressure over the last 30 years is consistent with N2 condensation taking place in the northern hemisphere. However, models typically predict a steady decrease in the surface pressure for the period 2005-2060, which is not confirmed by this observation. Complex surface-atmosphere interactions, such as ice albedo runaway and formation of local N2 frosts in the equatorial regions of Triton, could explain the relatively constant pressure between 2017 and 2022.

  • 105. Singh, V.
    et al.
    Brandeker, Alexis
    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.
    Zingales, T.
    CHEOPS observations of KELT-20 b/MASCARA-2 b: An aligned orbit and signs of variability from a reflective day side2024Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 683, artikkel-id A1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. Occultations are windows of opportunity to indirectly peek into the dayside atmosphere of exoplanets. High-precision transit events provide information on the spin-orbit alignment of exoplanets around fast-rotating hosts.

    Aims. We aim to precisely measure the planetary radius and geometric albedo of the ultra-hot Jupiter (UHJ) KELT-20 b along with the spin-orbit alignment of the system.

    Methods. We obtained optical high-precision transits and occultations of KELT-20 b using CHEOPS observations in conjunction with simultaneous TESS observations. We interpreted the occultation measurements together with archival infrared observations to measure the planetary geometric albedo and dayside temperatures. We further used the host star’s gravity-darkened nature to measure the system’s obliquity.

    Results. We present a time-averaged precise occultation depth of 82 ± 6 ppm measured with seven CHEOPS visits and from the analysis of all available TESS photometry. Using these measurements, we precisely constrain the geometric albedo of KELT-20 b to 0.26 ± 0.04 and the brightness temperature of the dayside hemisphere to K. Assuming Lambertian scattering law, we constrain the Bond albedo to along with a minimal heat transfer to the night side (ϵ = ). Furthermore, using five transit observations we provide stricter constraints of 3 9 ± 1 1 deg on the sky-projected obliquity of the system.

    Conclusions. The aligned orbit of KELT-20 b is in contrast to previous CHEOPS studies that have found strongly inclined orbits for planets orbiting other A-type stars. The comparably high planetary geometric albedo of KELT-20 b corroborates a known trend of strongly irradiated planets being more reflective. Finally, we tentatively detect signs of temporal variability in the occultation depths, which might indicate variable cloud cover advecting onto the planetary day side.

  • 106. Swayne, M I
    et al.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Wilson, T G
    The EBLM Project- XI. Mass, radius, and effective temperature measurements for 23 M-dwarf companions to solar-type stars observed with CHEOPS2024Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 528, nr 4, s. 5703-5722Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Observations of low-mass stars have frequently shown a disagreement between observed stellar radii and radii predicted by theoretical stellar structure models. This 'radius inflation' problem could have an impact on both stellar and exoplanetary science. We present the final results of our observation programme with the CHaracterising ExOPlanet Satellite (CHEOPS) to obtain high-precision light curves of eclipsing binaries with low-mass stellar companions (EBLMs). Combined with the spectroscopic orbits of the solar-type companions, we can derive the masses, radii, and effective temperatures of 23 M-dwarf stars. We use the pycheops data analysis software to analyse their primary and secondary occultations. For all but one target, we also perform analyses with Transiting Exoplanet Survey Satellite (TESS) light curves for comparison. We have assessed the impact of starspot-induced variation on our derived parameters and account for this in our radius and effective temperature uncertainties using simulated light curves. We observe trends in inflation with both metallicity and orbital separation. We also observe a strong trend in the difference between theoretical and observational effective temperatures with metallicity. There is no such trend with orbital separation. These results are not consistent with the idea that the observed inflation in stellar radius combines with lower effective temperature to preserve the luminosity predicted by low-mass stellar models. Our EBLM systems provide high-quality and homogeneous measurements that can be used in further studies of radius inflation.

  • 107. Swayne, M.
    et al.
    Maxted, P. F. L.
    Triaud, A. H. M. J.
    Sousa, S. G.
    Broeg, C.
    Florén, Hans Gustav Axel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Guterman, P.
    Simon, A. E.
    Boisse, I.
    Bonfanti, A.
    Martin, D.
    Santerne, A.
    Salmon, S.
    Standing, M. R.
    Van Grootel, V.
    Wilson, T. G.
    Alibert, Y.
    Alonso, R.
    Anglada Escudé, G.
    Asquier, J.
    Bárczy, T.
    Barrado, D.
    Barros, S. C. C.
    Battley, M.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Bekkelien, A.
    Benz, W.
    Billot, N.
    Bonfils, X.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Busch, M.-D.
    Cabrera, J.
    Charnoz, S.
    Collier Cameron, A.
    Csizmadia, Sz.
    Davies, M. B.
    Deleuil, M.
    Deline, A.
    Delrez, L.
    Demangeon, O. D. S.
    Demory, B.-O.
    Dransfield, G.
    Ehrenreich, D.
    Erikson, A.
    Fortier, A.
    Fossati, L.
    Fridlund, M.
    Futyan, D.
    Gandolfi, D.
    Gillon, M.
    Guedel, M.
    Hébrard, G.
    Heidari, N.
    Hellier, C.
    Heng, K.
    Hobson, M.
    Hoyer, S.
    Isaak, K. G.
    Kiss, L.
    Kunovac Hodžić, V.
    Lalitha, S.
    Laskar, J.
    Lecavelier des Etangs, A.
    Lendl, M.
    Lovis, C.
    Magrin, D.
    Marafatto, L.
    McCormac, J.
    Miller, N.
    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.
    Santos, N. C.
    Scandariato, G.
    Ségransan, D.
    Smith, A. M. S.
    Steinberger, M.
    Steller, M.
    Szabó, Gy. M.
    Thomas, N.
    Udry, S.
    Walter, I.
    Walton, N. A.
    Willett, E.
    The EBLM project – VIII. First results for M-dwarf mass, radius, and effective temperature measurements using CHEOPS light curves 2021Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 506, nr 1, s. 306-322Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The accuracy of theoretical mass, radius, and effective temperature values for M-dwarf stars is an active topic of debate. Differences between observed and theoretical values have raised the possibility that current theoretical stellar structure and evolution models are inaccurate towards the low-mass end of the main sequence. To explore this issue, we use the CHEOPS satellite to obtain high-precision light curves of eclipsing binaries with low-mass stellar companions. We use these light curves combined with the spectroscopic orbit for the solar-type companion to measure the mass, radius, and effective temperature of the M-dwarf star. Here, we present the analysis of three eclipsing binaries. We use the PYCHEOPS data analysis software to fit the observed transit and eclipse events of each system. Two of our systems were also observed by the TESS satellite – we similarly analyse these light curves for comparison. We find consistent results between CHEOPS and TESS, presenting three stellar radii and two stellar effective temperature values of low-mass stellar objects. These initial results from our on-going observing programme with CHEOPS show that we can expect to have ∼24 new mass, radius, and effective temperature measurements for very low-mass stars within the next few years.

  • 108. Szabo, Gy M.
    et al.
    Gandolfi, D.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Csizmadia, Sz
    Garai, Z.
    Billot, N.
    Broeg, C.
    Ehrenreich, D.
    Fortier, A.
    Fossati, L.
    Hoyer, S.
    Kiss, L.
    Lecavelier des Etangs, A.
    Maxted, P. F. L.
    Ribas, I.
    Alibert, Y.
    Alonso, R.
    Anglada Escude, G.
    Barczy, T.
    Barros, S. C. C.
    Barrado, D.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Bekkelien, A.
    Bonfils, X.
    Benz, W.
    Borsato, L.
    Busch, M.-D.
    Cabrera, J.
    Charnoz, S.
    Collier Cameron, A.
    Corral Van Damme, C.
    Davies, M. B.
    Delrez, L.
    Deleuil, M.
    Demangeon, O. D. S.
    Demory, B.-O.
    Erikson, A.
    Fridlund, M.
    Futyan, D.
    Garcia Munoz, A.
    Gillon, M.
    Guedel, M.
    Guterman, P.
    Heng, K.
    Isaak, K. G.
    Lacedelli, G.
    Laskar, J.
    Lendl, M.
    Lovis, C.
    Luntzer, A.
    Magrin, D.
    Nascimbeni, V.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Osborn, H. P.
    Ottensamer, R.
    Pagano, I.
    Palle, E.
    Peter, G.
    Piazza, D.
    Piotto, G.
    Pollacco, D.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Rauer, H.
    Santos, N. C.
    Scandariato, G.
    Segransan, D.
    Serrano, L. M.
    Sicilia, D.
    Simon, A. E.
    Smith, A. M. S.
    Sousa, S. G.
    Steller, M.
    Thomas, N.
    Udry, S.
    Van Grootel, V.
    Walton, N. A.
    Wilson, T. G.
    The changing face of AU Mic b: stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS2021Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 654, artikkel-id A159Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    AU Mic is a young planetary system with a resolved debris disc showing signs of planet formation and two transiting warm Neptunes near mean-motion resonances. Here we analyse three transits of AU Mic b observed with the CHaracterising ExOPlanet Satellite (CHEOPS), supplemented with sector 1 and 27 Transiting Exoplanet Survey Satellite (TESS) photometry, and the All-Sky Automated Survey from the ground. The refined orbital period of AU Mic b is 8.462995 +/- 0.000003 d, whereas the stellar rotational period is P-rot = 4.8367 +/- 0.0006 d. The two periods indicate a 7:4 spin-orbit commensurability at a precision of 0.1%. Therefore, all transits are observed in front of one of the four possible stellar central longitudes. This is strongly supported by the observation that the same complex star-spot pattern is seen in the second and third CHEOPS visits that were separated by four orbits (and seven stellar rotations). Using a bootstrap analysis we find that flares and star spots reduce the accuracy of transit parameters by up to 10% in the planet-to-star radius ratio and the accuracy on transit time by 3-4 min. Nevertheless, occulted stellar spot features independently confirm the presence of transit timing variations (TTVs) with an amplitude of at least 4 min. We find that the outer companion, AU Mic c, may cause the observed TTVs.

  • 109. Szabó, Gy. M.
    et al.
    Garai, Z.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Gandolfi, D.
    Wilson, T. G.
    Deline, A.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Fortier, A.
    Queloz, D.
    Borsato, L.
    Kiefer, F.
    Lecavelier des Etangs, A.
    Lendl, M.
    Serrano, L. M.
    Sulis, S.
    Ulmer Moll, S.
    Van Grootel, V.
    Alibert, Y.
    Alonso, R.
    Anglada, G.
    Bárczy, T.
    Barrado y Navascues, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Benz, W.
    Billot, N.
    Bonfanti, A.
    Bonfils, X.
    Broeg, C.
    Cabrera, J.
    Charnoz, S.
    Collier Cameron, A.
    Csizmadia, Sz.
    Davies, M. B.
    Deleuil, M.
    Delrez, L.
    Demangeon, O.
    Demory, B.-O.
    Ehrenreich, D.
    Erikson, A.
    Fossati, L.
    Fridlund, M.
    Gillon, M.
    Güdel, M.
    Heng, K.
    Hoyer, S.
    Isaak, K. G.
    Kiss, L. L.
    Laskar, J.
    Lovis, C.
    Magrin, D.
    Maxted, P. F. L.
    Mecina, M.
    Nascimbeni, V.
    Ottensamer, R.
    Pagano, I.
    Pallé, E.
    Peter, G.
    Piotto, G.
    Pollacco, D.
    Ragazzoni, R.
    Rando, N.
    Rauer, H.
    Ribas, I.
    Santos, N. C.
    Sarajlic, M.
    Scandariato, G.
    Ségransan, D.
    Simon, A. E.
    Smith, A. M. S.
    Sousa, S. G.
    Steller, M.
    Thomas, N.
    Udry, S.
    Verrecchia, F.
    Walton, N.
    Wolter, D.
    Transit timing variations of AU Microscopii b and c2022Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 659, artikkel-id L7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Here we report large-amplitude transit timing variations (TTVs) for AU Microcopii b and c as detected in combined TESS (2018, 2020) and CHEOPS (2020, 2021) transit observations. AU Mic is a young planetary system with a debris disk and two transiting warm Neptunes. A TTV on the order of several minutes was previously reported for AU Mic b, which was suggested to be an outcome of mutual perturbations between the planets in the system. In 2021, we observed AU Mic b (five transits) and c (three transits) with the CHEOPS space telescope to follow-up the TTV of AU Mic b and possibly detect a TTV for AU Mic c. When analyzing TESS and CHEOPS 2020-2021 measurements together, we find that a prominent TTV emerges with a full span of >= 23 min between the two TTV extrema. Assuming that the period change results from a periodic process -such as mutual perturbations- we demonstrate that the times of transits in the summer of 2022 are expected to be 30-85 min later than predicted by the available linear ephemeris.

  • 110. Tuson, A.
    et al.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Patel, Jayshil Ashokkumar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Wohler, B.
    TESS and CHEOPS discover two warm sub-Neptunes transiting the bright K-dwarf HD 159062023Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 523, nr 2, s. 3090-3118Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report the discovery of two warm sub-Neptunes transiting the bright (G = 9.5 mag) K-dwarf HD 15906 (TOI461, TIC 4646810). This star was observed by the Transiting Exoplanet Survey Satellite (TESS) in sectors 4 and 31, revealing two small transiting planets. The inner planet, HD 15906 b, was detected with an unambiguous period but the outer planet, HD 15906 c, showed only two transits separated by similar to 734 d, leading to 36 possible values of its period. We performed follow-up observations with the CHaracterising ExOPlanet Satellite (CHEOPS) to confirm the true period of HD 15906 c and improve the radius precision of the two planets. From TESS, CHEOPS, and additional ground-based photometry, we find that HD 15906 b has a radius of 2.24 +/- 0.08 R-circle plus and a period of 10.924709 +/- 0.000032 d, whilst HD 15906 c has a radius of 2.93(-0.06)(+0.07) R-circle plus and a period of 21.583298(-0.000055)(+0.000052) d. Assuming zero bond albedo and full day-night heat redistribution, the inner and outer planet have equilibrium temperatures of 668 +/- 13 K and 532 +/- 10 K, respectively. The HD 15906 system has become one of only six multiplanet systems with two warm (less than or similar to 700 K) sub-Neptune sized planets transiting a bright star (G <= 10 mag). It is an excellent target for detailed characterization studies to constrain the composition of sub-Neptune planets and test theories of planet formation and evolution.

  • 111. Ulmer-Moll, S.
    et al.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Walton, N. A.
    TOI-5678 b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS2023Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 674, artikkel-id A43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. A large sample of long-period giant planets has been discovered thanks to long-term radial velocity surveys, but only a few dozen of these planets have a precise radius measurement. Transiting gas giants are crucial targets for the study of atmospheric composition across a wide range of equilibrium temperatures and, more importantly, for shedding light on the formation and evolution of planetary systems. Indeed, compared to hot Jupiters, the atmospheric properties and orbital parameters of cooler gas giants are unaltered by intense stellar irradiation and tidal effects. Aims. We aim to identify long-period planets in the Transiting Exoplanet Survey Satellite (TESS) data as single or duo-transit events. Our goal is to solve the orbital periods of TESS duo-transit candidates with the use of additional space-based photometric observations and to collect follow-up spectroscopic observations in order to confirm the planetary nature and measure the mass of the candidates. Methods. We use the CHaracterising ExOPlanet Satellite (CHEOPS) to observe the highest-probability period aliases in order to discard or confirm a transit event at a given period. Once a period is confirmed, we jointly model the TESS and CHEOPS light curves along with the radial velocity datasets to measure the orbital parameters of the system and obtain precise mass and radius measurements. Results. We report the discovery of a long-period transiting Neptune-mass planet orbiting the G7-type star TOI-5678. Our spectroscopic analysis shows that TOI-5678 is a star with a solar metallicity. The TESS light curve of TOI-5678 presents two transit events separated by almost two years. In addition, CHEOPS observed the target as part of its Guaranteed Time Observation program. After four non-detections corresponding to possible periods, CHEOPS detected a transit event matching a unique period alias. Follow-up radial velocity observations were carried out with the ground-based high-resolution spectrographs CORALIE and HARPS. Joint modeling reveals that TOI-5678 hosts a 47.73 day period planet, and we measure an orbital eccentricity consistent with zero at 2s. The planet TOI-5678 b has a mass of 20 +/- 4 Earth masses (M-circle plus) and a radius of 4.91 +/- 0.08 R-circle plus Using interior structure modeling, we find that TOI-5678 b is composed of a low-mass core surrounded by a large H/He layer with a mass of 3.2(-1.3)(+1.7) M-circle plus. Conclusions. TOI-5678 b is part of a growing sample of well-characterized transiting gas giants receiving moderate amounts of stellar insolation (11 S circle plus). Precise density measurement gives us insight into their interior composition, and the objects orbiting bright stars are suitable targets to study the atmospheric composition of cooler gas giants.

  • 112. Van Grootel, V.
    et al.
    Pozuelos, F. J.
    Thuillier, A.
    Charpinet, S.
    Delrez, L.
    Beck, M.
    Fortier, A.
    Hoyer, S.
    Sousa, S. G.
    Barlow, B. N.
    Billot, N.
    Dévora-Pajares, M.
    Østensen, R. H.
    Alibert, Y.
    Alonso, R.
    Anglada Escudé, G.
    Asquier, J.
    Barrado, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, T.
    Bekkelien, A.
    Benz, W.
    Bonfils, X.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Broeg, C.
    Bruno, G.
    Bárczy, T.
    Cabrera, J.
    Cameron, A. C.
    Charnoz, S.
    Davies, M. B.
    Deleuil, M.
    Demangeon, O. D. S.
    Demory, B-O.
    Ehrenreich, D.
    Erikson, A.
    Fossati, L.
    Fridlund, M.
    Futyan, D.
    Gandolfi, D.
    Gillon, M.
    Guedel, M.
    Heng, K.
    Isaak, K. G.
    Kiss, L.
    Laskar, J.
    Lecavelier des Etangs, A.
    Lendl, M.
    Lovis, C.
    Magrin, D.
    Maxted, P. F. L.
    Mecina, M.
    Mustill, A. J.
    Nascimbeni, V.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ottensamer, R.
    Pagano, I.
    Pallé, E.
    Peter, G.
    Piotto, G.
    Plesseria, J-Y.
    Pollacco, D.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Rauer, H.
    Ribas, I.
    Santos, N. C.
    Scandariato, G.
    Ségransan, D.
    Silvotti, R.
    Simon, A. E.
    Smith, A. M. S.
    Steller, M.
    Szabó, G. M.
    Thomas, N.
    Udry, S.
    Viotto, V.
    Walton, N. A.
    Westerdorff, K.
    Wilson, T. G.
    A search for transiting planets around hot subdwarfs I. Methods and performance tests on light curves from Kepler, K2, TESS, and CHEOPS2021Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 650, artikkel-id A205Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. Hot subdwarfs experienced strong mass loss on the red giant branch (RGB) and are now hot and small He-burning objects. These stars constitute excellent opportunities for addressing the question of the evolution of exoplanetary systems directly after the RGB phase of evolution.

    Aims. In this project we aim to perform a transit survey in all available light curves of hot subdwarfs from space-based telescopes (Kepler, K2, TESS, and CHEOPS) with our custom-made pipeline SHERLOCK in order to determine the occurrence rate of planets around these stars as a function of orbital period and planetary radius. We also aim to determine whether planets that were previously engulfed in the envelope of their red giant host star can survive, even partially, as a planetary remnant.

    Methods. For this first paper, we performed injection-and-recovery tests of synthetic transits for a selection of representative Kepler, K2, and TESS light curves to determine which transiting bodies in terms of object radius and orbital period we will be able to detect with our tools. We also provide estimates for CHEOPS data, which we analyzed with the pycheops package.

    Results. Transiting objects with a radius ≲1.0 R can be detected in most of the Kepler, K2, and CHEOPS targets for the shortest orbital periods (1 d and shorter), reaching values as low as ~0.3 R in the best cases. Sub-Earth-sized bodies are only reached for the brightest TESS targets and for those that were observed in a significant number of sectors. We also give a series of representative results for larger planets at greater distances, which strongly depend on the target magnitude and on the length and quality of the data.

    Conclusions. The TESS sample will provide the most important statistics for the global aim of measuring the planet occurrence rate around hot subdwarfs. The Kepler, K2, and CHEOPS data will allow us to search for planetary remnants, that is, very close and small (possibly disintegrating) objects.

  • 113. Vandenbussche, B.
    et al.
    Sibthorpe, B.
    Acke, B.
    Pantin, E.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Waelkens, C.
    Dominik, C.
    Barlow, M. J.
    Blommaert, J. A. D. L.
    Bouwman, J.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Cohen, M.
    De Meester, W.
    Dent, W. R. F.
    Exter, K.
    Di Francesco, J.
    Fridlund, M.
    Gear, W. K.
    Glauser, A. M.
    Gomez, H. L.
    Greaves, J. S.
    Hargrave, P. C.
    Harvey, P. M.
    Henning, Th.
    Heras, A. M.
    Hogerheijde, M. R.
    Holland, W. S.
    Huygen, R.
    Ivison, R. J.
    Jean, C.
    Leeks, S. J.
    Lim, T. L.
    Liseau, R.
    Matthews, B. C.
    Naylor, D. A.
    Pilbratt, G. L.
    Polehampton, E. T.
    Regibo, S.
    Royer, P.
    Sicilia-Aguilar, A.
    Swinyard, B. M.
    Walker, H. J.
    Wesson, R.
    The beta Pictoris disk imaged by Herschel PACS and SPIRE2010Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 518, s. L133-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We obtained Herschel PACS and SPIRE images of the thermal emission of the debris disk around the A5V star beta Pic. The disk is well resolved in the PACS filters at 70, 100, and 160 mu m. The surface brightness profiles between 70 and 160 mu m show no significant asymmetries along the disk, and are compatible with 90% of the emission between 70 and 160 mu m originating in a region closer than 200 AU to the star. Although only marginally resolving the debris disk, the maps obtained in the SPIRE 250-500 mu m filters provide full-disk photometry, completing the SED over a few octaves in wavelength that had been previously inaccessible. The small far-infrared spectral index (beta = 0.34) indicates that the grain size distribution in the inner disk (<200 AU) is inconsistent with a local collisional equilibrium. The size distribution is either modified by non-equilibrium effects, or exhibits a wavy pattern, caused by an under-abundance of impactors which have been removed by radiation pressure.

  • 114. Wilson, Thomas G.
    et al.
    Goffo, Elisa
    Alibert, Yann
    Gandolfi, Davide
    Bonfanti, Andrea
    Persson, Carina M.
    Collier Cameron, Andrew
    Fridlund, Malcolm
    Fossati, Luca
    Korth, Judith
    Benz, Willy
    Deline, Adrien
    Florén, Hans-Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Guterman, Pascal
    Adibekyan, Vardan
    Hooton, Matthew J.
    Hoyer, Sergio
    Leleu, Adrien
    Mustill, Alexander James
    Salmon, Sebastien
    Sousa, Sergio G.
    Suarez, Olga
    Abe, Lyu
    Agabi, Abdelkrim
    Alonso, Roi
    Anglada, Guillem
    Asquier, Joel
    Barczy, Tamas
    Barrado Navascues, David
    Barros, Susana C. C.
    Baumjohann, Wolfgang
    Beck, Mathias
    Beck, Thomas
    Billot, Nicolas
    Bonfils, Xavier
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Broeg, Christopher
    Bryant, Edward M.
    Burleigh, Matthew R.
    Buttu, Marco
    Cabrera, Juan
    Charnoz, Sebastien
    Ciardi, David R.
    Cloutier, Ryan
    Cochran, William D.
    Collins, Karen A.
    Colon, Knicole D.
    Crouzet, Nicolas
    Csizmadia, Szilard
    Davies, Melvyn B.
    Deleuil, Magali
    Delrez, Laetitia
    Demangeon, Olivier
    Demory, Brice-Olivier
    Dragomir, Diana
    Dransfield, Georgina
    Ehrenreich, David
    Erikson, Anders
    Fortier, Andrea
    Gan, Tianjun
    Gill, Samuel
    Gillon, Michael
    Gnilka, Crystal L.
    Grieves, Nolan
    Grziwa, Sascha
    Gudel, Manuel
    Guillot, Tristan
    Haldemann, Jonas
    Heng, Kevin
    Horne, Keith
    Howell, Steve B.
    Isaak, Kate G.
    Jenkins, Jon M.
    Jensen, Eric L. N.
    Kiss, Laszlo
    Lacedelli, Gaia
    Lam, Kristine
    Laskar, Jacques
    Latham, David W.
    Lecavelier des Etangs, Alain
    Lendl, Monika
    Lester, Kathryn
    Levine, Alan M.
    Livingston, John
    Lovis, Christophe
    Luque, Rafael
    Magrin, Demetrio
    Marie-Sainte, Wenceslas
    Maxted, Pierre F. L.
    Mayo, Andrew W.
    McLean, Brian
    Mecina, Marko
    Mekarnia, Djamel
    Nascimbeni, Valerio
    Nielsen, Louise D.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Osborn, Hugh P.
    Osborne, Hannah L. M.
    Ottensamer, Roland
    Pagano, Isabella
    Palle, Enric
    Peter, Gisbert
    Piotto, Giampaolo
    Pollacco, Don
    Queloz, Didier
    Ragazzoni, Roberto
    Rando, Nicola
    Rauer, Heike
    Redfield, Seth
    Ribas, Ignasi
    Ricker, George R.
    Rieder, Martin
    Santos, Nuno C.
    Scandariato, Gaetano
    Schmider, Francois-Xavier
    Schwarz, Richard P.
    Scott, Nicholas J.
    Seager, Sara
    Segransan, Damien
    Serrano, Luisa Maria
    Simon, Attila E.
    Smith, Alexis M. S.
    Steller, Manfred
    Stockdale, Chris
    Szabo, Gyula
    Thomas, Nicolas
    Ting, Eric B.
    Triaud, Amaury H. M. J.
    Udry, Stephane
    Van Eylen, Vincent
    Van Grootel, Valerie
    Vanderspek, Roland K.
    Viotto, Valentina
    Walton, Nicholas
    Winn, Joshua N.
    A pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 characterized with CHEOPS2022Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 511, nr 1, s. 1043-1071Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report the discovery and characterization of a pair of sub-Neptunes transiting the bright K-dwarf TOI-1064 (TIC 79748331), initially detected in the Transiting Exoplanet Survey Satellite (TESS) photometry. To characterize the system, we performed and retrieved the CHaracterising ExOPlanets Satellite (CHEOPS), TESS, and ground-based photometry, the High Accuracy Radial velocity Planet Searcher (HARPS) high-resolution spectroscopy, and Gemini speckle imaging. We characterize the host star and determine Teff,⋆=4734±67K⁠, R⋆=0.726±0.007R⊙⁠, and M⋆=0.748±0.032M⊙⁠. We present a novel detrending method based on point spread function shape-change modelling and demonstrate its suitability to correct flux variations in CHEOPS data. We confirm the planetary nature of both bodies and find that TOI-1064 b has an orbital period of Pb = 6.44387 ± 0.00003 d, a radius of Rb = 2.59 ± 0.04 R⊕, and a mass of Mb=13.5+1.7−1.8 M⊕, whilst TOI-1064 c has an orbital period of Pc=12.22657+0.00005−0.00004 d, a radius of Rc = 2.65 ± 0.04 R⊕, and a 3σ upper mass limit of 8.5 M⊕. From the high-precision photometry we obtain radius uncertainties of ∼1.6 per cent, allowing us to conduct internal structure and atmospheric escape modelling. TOI-1064 b is one of the densest, well-characterized sub-Neptunes, with a tenuous atmosphere that can be explained by the loss of a primordial envelope following migration through the protoplanetary disc. It is likely that TOI-1064 c has an extended atmosphere due to the tentative low density, however further radial velocities are needed to confirm this scenario and the similar radii, different masses nature of this system. The high-precision data and modelling of TOI-1064 b are important for planets in this region of mass–radius space, and it allow us to identify a trend in bulk density–stellar metallicity for massive sub-Neptunes that may hint at the formation of this population of planets.

  • 115. Xie, Ji-Wei
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Wu, Yanqin
    ON THE UNUSUAL GAS COMPOSITION IN THE beta PICTORIS DEBRIS DISK2013Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 762, nr 2, s. 114-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Themetallic gas associated with the beta Pic debris disk is not believed to be primordial, but arises from the destruction of dust grains. Recent observations have shown that carbon and oxygen in this gas are exceptionally overabundant compared to other elements, by some 400 times. We study the origin of this enrichment under two opposing hypotheses: preferential production, where the gas is produced with the observed unusual abundance (as may happen if gas is produced by photodesorption from C/O-rich icy grains), and preferential depletion, where the gas evolves to the observed state from an original solar abundance (if outgassing occurs under high-speed collisions) under a number of dynamical processes. We include in our study the following processes: radiative blowout of metallic elements, dynamical coupling between different species, and viscous accretion onto the star. We find that, if gas viscosity is sufficiently low (the conventional a parameter less than or similar to 10(-3)), differential blowout dominates. While gas accumulates gradually in the disks, metallic elements subject to strong radiation forces, such as Na and Fe, deplete more quickly than C and O, naturally leading to the observed overabundance of C and O. On the other hand, if gas viscosity is high (alpha greater than or similar to 10(-1), as expected for this largely ionized disk), gas is continuously produced and viscously accreted toward the star. This removal process does not discriminate between elements so the observed overabundance of C and O has to be explained by a preferential production that strongly favors C and O to other metallic elements. One such candidate is photodesorption off the grains. We compare our calculation against all observed elements (similar to 10) in the gas disk and find a mild preference for the second scenario, based on the abundance of Si alone. If true, beta Pic should still be accreting at an observable rate, well after its primordial disk has disappeared.

  • 116. Youngblood, Allison
    et al.
    Roberge, Aki
    MacGregor, Meredith A.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Weinberger, Alycia J.
    Pérez, Sebastián
    Grady, Carol
    Welsh, Barry
    A Radiatively Driven Wind from the η Tel Debris Disk2021Inngår i: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 162, nr 6, artikkel-id 235Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present far- and near-ultraviolet absorption spectroscopy of the ∼23 Myr edge-on debris disk surrounding the A0V star η Telescopii, obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph. We detect absorption lines from C i, C ii, O i, Mg ii, Al ii, Si ii, S ii, Mn ii, Fe ii, and marginally N i. The lines show two clear absorption components at −22.7 ± 0.5 km s−1 and −17.8 ± 0.7 km s−1, which we attribute to circumstellar (CS) and interstellar gas, respectively. CO absorption is not detected, and we find no evidence for star-grazing exocomets. The CS absorption components are blueshifted by −16.9 ± 2.6 km s−1 in the star's reference frame, indicating that they are outflowing in a radiatively driven disk wind. We find that the C/Fe ratio in the η Tel CS gas is significantly higher than the solar ratio, as is the case in the β Pic and 49 Cet debris disks. Unlike those disks, however, the measured C/O ratio in the η Tel CS gas is consistent with the solar value. Our analysis shows that because η Tel is an earlier type star than β Pic and 49 Cet, with more substantial radiation pressure at the dominant C ii transitions, this species cannot bind the CS gas disk to the star as it does for β Pic and 49 Cet, resulting in the disk wind.

  • 117. Zagorovsky, Kyryl
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Wu, Yanqin
    GAS EMISSION FROM DEBRIS DISKS AROUND A AND F STARS2010Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 720, nr 1, s. 923-939Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Gas has been detected in a number of debris disk systems. This gas may have arisen from grain sublimation or grain photodesorption. It interacts with the surrounding dust grains through a number of charge and heat exchanges. Studying the chemical composition and physical state of this gas can therefore reveal much about the dust component in these debris disks. We have produced a new code, ONTARIO, to address gas emission from dusty gas-poor disks around A-F stars. This code computes the gas ionization and thermal balance self-consistently, with particular care taken of heating/cooling mechanisms. Line emission spectra are then produced for each species (up to zinc) by statistical equilibrium calculations of the atomic/ionic energy levels. For parameters that resemble the observed beta Pictoris gas disk, we find that the gas is primarily heated by photoelectric emission from dust grains, and primarily cooled through the CII 157.7 mu m line emission. The gas can be heated to a temperature that is warmer than that of the dust and may in some cases reach temperature for thermal escape. The dominant cooling line, CII 157.7 mu m, should be detectable by Herschel in these disks, while the OI 63.2 mu m line will be too faint. We also study the dependence of the cooling line fluxes on a variety of disk parameters, in light of the much improved sensitivity to thermal line emission in the mid/far-infrared and at submillimeter wavelengths provided by, in particular, Herschel, SOFIA, and ALMA. These new instruments will yield much new information about dusty debris disks.

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