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  • 51.
    Grigorieva, Anna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Thebault, Philippe
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Artymowicz, Pawel
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Survival of icy grains in debris discs. The role of photosputtering2007Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We put theoretical constraints on the presence and survival of icy grains in debris discs. Particular attention is paid to UV sputtering of water ice, which has so far not been studied in detail in this context. We present a photosputtering model based on available experimental and theoretical studies. We quantitatively estimate the erosion rate of icy and ice-silicate grains, under the influence of both sublimation and photosputtering, as a function of grain size, composition and distance from the star. The effect of erosion on the grain's location is investigated through numerical simulations coupling the grain size to its dynamical evolution. Our model predicts that photodesorption efficiently destroy ice in optically thin discs, even far beyond the sublimation snow line. For the reference case of beta Pictoris, we find that only > 5mm grains can keep their icy component for the age of the system in the 50-150AU region. When taking into account the collisional reprocessing of grains, we show that the water ice survival on grains improves (grains down to ~ 20 um might be partially icy). However, estimates of the amount of gas photosputtering would produce on such a hypothetical population of big icy grains lead to values for the OI column density that strongly exceed observational constraints for beta Pic, thus ruling out the presence of a significant amount of icy grains in this system. Erosion rates and icy grains survival timescales are also given for a set of 11 other debris disc systems. We show that, with the possible exception of M stars, photosputtering cannot be neglected in calculations of icy grain lifetimes.

  • 52.
    Grigorieva, Anna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Thébault, Philippe
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Artymowicz, Pawel
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Survival of icy grains in debris discs. The role of photosputtering2007Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Astronomy and Astrophysics, ISSN 0004-6361, Vol. 475, nr 2, s. 755-764Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aims.We put theoretical constraints on the presence and survival of icy grains in debris discs. Particular attention is paid to UV sputtering of water ice, which has so far not been studied in detail in this context.

    Methods: We present a photosputtering model based on available experimental and theoretical studies. We quantitatively estimate the erosion rate of icy and ice-silicate grains, under the influence of both sublimation and photosputtering, as a function of grain size, composition and distance from the star. The effect of erosion on the grain's location is investigated through numerical simulations coupling the grain size to its dynamical evolution.

    Results: Our model predicts that photodesorption efficiently destroy ice in optically thin discs, even far beyond the sublimation snow line. For the reference case of β Pictoris, we find that only ⪆5 mm grains can keep their icy component for the age of the system in the 50-150 AU region. When taking into account the collisional reprocessing of grains, we show that the water ice survival on grains improves (grains down to ≃20 μm might be partially icy). However, estimates of the amount of gas photosputtering would produce on such a hypothetical population of big icy grains lead to values for the O I column density that strongly exceed observational constraints for β Pic, thus ruling out the presence of a significant amount of icy grains in this system. Erosion rates and icy grains survival timescales are also given for a set of 11 other debris disc systems. We show that, with the possible exception of M stars, photosputtering cannot be neglected in calculations of icy grain lifetimes.

  • 53. Hawthorn, Faith
    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).
    Zhang, Hui
    TOI-836: A super-Earth and mini-Neptune transiting a nearby K-dwarf2023Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 520, nr 3, s. 3649-3668Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364) using data from TESS Sector 11 and Sector 38. TOI-836 is a bright (T = 8.5 mag), high proper motion (similar to 200 mas yr(-1)), low metallicity ([Fe/H]asymptotic to-0.28) K-dwarf with a mass of 0.68 +/- 0.05 M-? and a radius of 0.67 +/- 0.01 R-?. We obtain photometric follow-up observations with a variety of facilities, and we use these data sets to determine that the inner planet, TOI-836 b, is a 1.70 +/- 0.07 R-circle plus super-Earth in a 3.82-d orbit, placing it directly within the so-called radius valley'. The outer planet, TOI-836 c, is a 2.59 +/- 0.09 R-circle plus mini-Neptune in an 8.60-d orbit. Radial velocity measurements reveal that TOI-836 b has a mass of 4.5 +/- 0.9 M-circle plus, while TOI-836 c has a mass of 9.6 +/- 2.6 M-circle plus. Photometric observations show Transit Timing Variations (TTVs) on the order of 20 min for TOI-836 c, although there are no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by an undetected exterior planet

  • 54. Hooton, M. J.
    et al.
    Hoyer, S.
    Kitzmann, D.
    Morris, B. M.
    Smith, A. M. S.
    Collier Cameron, A.
    Futyan, D.
    Maxted, P. F. L.
    Queloz, D.
    Demory, B.-O.
    Heng, K.
    Lendl, M.
    Cabrera, J.
    Csizmadia, Sz.
    Deline, A.
    Parviainen, H.
    Salmon, S.
    Sulis, S.
    Wilson, T. G.
    Bonfanti, A.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Demangeon, O. D. S.
    Oshagh, M.
    Persson, C. M.
    Scandariato, G.
    Alibert, Y.
    Alonso, R.
    Anglada Escude, G.
    Barczy, T.
    Barrado, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Benz, W.
    Billot, N.
    Bonfils, X.
    Bourrier, V.
    Broeg, C.
    Busch, M.-D.
    Charnoz, S.
    Davies, M. B.
    Deleuil, M.
    Delrez, L.
    Ehrenreich, D.
    Erikson, A.
    Farinato, J.
    Fortier, A.
    Fossati, L.
    Fridlund, M.
    Gandolfi, D.
    Gillon, M.
    Gudel, M.
    Isaak, K. G.
    Jones, K.
    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.
    Palle, E.
    Peter, G.
    Piotto, G.
    Pollacco, D.
    Ragazzoni, R.
    Rando, N.
    Ratti, F.
    Rauer, H.
    Ribas, I.
    Santos, N. C.
    Segransan, D.
    Simon, A. E.
    Sousa, S. G.
    Steller, M.
    Szabo, Gy. M.
    Thomas, N.
    Udry, S.
    Ulmer, B.
    Van Grootel, V.
    Walton, N. A.
    Spi-OPS: Spitzer and CHEOPS confirm the near-polar orbit of MASCARA-1 b and reveal a hint of dayside reflection2022Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 658, artikkel-id A75Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. The light curves of tidally locked hot Jupiters transiting fast-rotating, early-type stars are a rich source of information about both the planet and star, with full-phase coverage enabling a detailed atmospheric characterisation of the planet. Although it is possible to determine the true spin-orbit angle Ψ - a notoriously difficult parameter to measure - from any transit asymmetry resulting from gravity darkening induced by the stellar rotation, the correlations that exist between the transit parameters have led to large disagreements in published values of Ψ for some systems.

    Aims. We aimed to study these phenomena in the light curves of the ultra-hot Jupiter MASCARA-1 b, which is characteristically similar to well-studied contemporaries such as KELT-9 b and WASP-33 b.

    Methods. We obtained optical CHaracterising ExOPlanet Satellite (CHEOPS) transit and occultation light curves of MASCARA-1 b, and analysed them jointly with a Spitzer/IRAC 4.5 µm full-phase curve to model the asymmetric transits, occultations, and phasedependent flux modulation. For the latter, we employed a novel physics-driven approach to jointly fit the phase modulation by generating a single 2D temperature map and integrating it over the two bandpasses as a function of phase to account for the differing planet-star flux contrasts. The reflected light component was modelled using the general ab initio solution for a semi-infinite atmosphere.

    Results. When fitting the CHEOPS and Spitzer transits together, the degeneracies are greatly diminished and return results consistent with previously published Doppler tomography. Placing priors informed by the tomography achieves even better precision, allowing a determination of Ψ = 72.1(-2.4)(+2.5) deg. From the occultations and phase variations, we derived dayside and nightside temperatures of 3062(-68)(+66) K and 1720 +/- 330 K, respectively. Our retrieval suggests that the dayside emission spectrum closely follows that of a blackbody. As the CHEOPS occultation is too deep to be attributed to blackbody flux alone, we could separately derive geometric albedo A(g) = 0.171(-0.068)(+0.066) and spherical albedo A(s) = 0.266(-0.100)(+0.097) from the CHEOPS data, and Bond albedo AB = 0.057(-0.101)(+0.083) from the Spitzer phase curve. Although small, the A(g) and A(s) indicate that MASCARA-1 b is more reflective than most other ultra-hot Jupiters, where H- absorption is expected to dominate.

    Conclusions. Where possible, priors informed by Doppler tomography should be used when fitting transits of fast-rotating stars, though multi-colour photometry may also unlock an accurate measurement of Ψ. Our approach to modelling the phase variations at different wavelengths provides a template for how to separate thermal emission from reflected light in spectrally resolved James Webb Space Telescope phase curve data.

  • 55.
    Janson, Markus
    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.
    Liseau, René
    The far reaches of the β Pictoris debris disk2021Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 646, artikkel-id A132Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The nearby young star beta Pictoris hosts a rich and complex planetary system, with at least two giant planets and a nearly edge-on debris disk that contains several dynamical subpopulations of planetesimals. While the inner ranges of the debris disk have been studied extensively, less information is known about the outer, fainter parts of the disk. Here we present an analysis of archival FORS V -band imaging data from 2003-2004, which have previously not been explored scientifically because the halo substructure of the bright stellar point spread function is complex. Through a high-contrast scheme based on angular differential imaging, with a forward-modelling approach to mitigate self-subtraction, we produced the deepest imaging yet for the outer range of the beta Pic disk, and extracted its morphological characteristics. A brightness asymmetry between the two arms of the edge-on disk, which was previously noted in the inner disk, is even more pronounced at larger angular separations, reaching a factor similar to 10 around 1000 AU. Approaching 2000 AU, the brighter arm is visible at a surface brightness of 27-28 mag arcsec(-2). Much like for the brightness asymmetry, a tilt angle asymmetry exists between the two arms that becomes increasingly extreme at large separations. The outer tilt angle of 7.2 deg can only be explained if the outer disk is farther from an edge-on inclination than the inner disk, or if its dust has a stronger scattering anisotropy, or (most likely) both. The strong asymmetries imply the presence of a highly eccentric kinematic disk component, which may have been caused by a disruptive event thought to have taken place at a closer-in location in the disk.

  • 56.
    Janson, Markus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Henning, Thomas
    Quanz, Sascha P.
    Asensio-Torres, Ruben
    Buchhave, Lars
    Krause, Oliver
    Palle, Enric
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Occulter to earth: prospects for studying earth-like planets with the E-ELT and a space-based occulter2022Inngår i: Experimental astronomy, ISSN 0922-6435, E-ISSN 1572-9508, Vol. 54, nr 2-3, s. 1223-1236Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Direct detection and characterization of Earth-like planets around Sun-like stars is a core task for evaluating the prevalence of habitability and life in the Universe. Here, we discuss a promising option for achieving this goal, which is based on placing an occulter in orbit and having it project its shadow onto the E-ELT at the surface of Earth, thus providing a sufficient contrast for imaging and taking spectra of Earth-like planets in the habitable zones of Sun-like stars. Doing so at a sensible fuel budget will require tailored orbits, an occulter with a high area-to-mass ratio, and appropriate instrumentation at the E-ELT. In this White Paper, submitted in response to the ESA Voyage 2050 Call, we outline the fundamental aspects of the concept, and the most important technical developments that will be required to develop a full mission.

  • 57. Janson, Markus
    et al.
    Jayawardhana, Ray
    Girard, Julien H.
    Lafreniere, David
    Bonavita, Mariangela
    Gizis, John
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    NEW BROWN DWARF COMPANIONS TO YOUNG STARS IN SCORPIUS-CENTAURUS2012Inngår i: The Astrophysical Journal Letters, ISSN 2041-8205, Vol. 758, nr 1, s. L2-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the discoveries of three faint companions to young stars in the Scorpius-Centaurus region, imaged with the NICI instrument on Gemini South. We have confirmed all three companions through common proper motion tests. Follow-up spectroscopy has confirmed two of them, HIP 65423 B and HIP 65517 B, to be brown dwarfs, while the third, HIP 72099 B, is more likely a very low mass star just above the hydrogen burning limit. The detection of wide companions in the mass range of similar to 40-100 M-jup complements previous work in the same region, reporting detections of similarly wide companions with lower masses, in the range of similar to 10-30 M-jup. Such low masses near the deuterium burning limit have raised the question of whether those objects formed like planets or stars. The existence of intermediate objects as reported here could represent a bridge between lower-mass companions and stellar companions, but in any case demonstrate that mass alone may not provide a clear-cut distinction for the formation of low-mass companions to stars.

  • 58. Janson, Markus
    et al.
    Lafreniere, David
    Jayawardhana, Ray
    Bonavita, Mariangela
    Girard, Julien H.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Gizis, John E.
    A MULTIPLICITY CENSUS OF INTERMEDIATE-MASS STARS IN SCORPIUS-CENTAURUS2013Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 773, nr 2, s. 170-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Stellar multiplicity properties have been studied for the lowest and the highest stellar masses, but intermediate-mass stars from F-type to late A-type have received relatively little attention. Here, we report on a Gemini/NICI snapshot imaging survey of 138 such stars in the young Scorpius-Centaurus (Sco-Cen) region, for the purpose of studying multiplicity with sensitivity down to planetary masses at wide separations. In addition to two brown dwarfs and a companion straddling the hydrogen-burning limit which we reported previously, here we present 26 new stellar companions and determine a multiplicity fraction within 0 ''.1-5 ''.0 of 21% +/- 4%. Depending on the adopted semimajor axis distribution, our results imply a total multiplicity in the range of similar to 60%-80%, which further supports the known trend of a smooth continuous increase in the multiplicity fraction as a function of primary stellar mass. A surprising feature in the sample is a distinct lack of nearly equal-mass binaries, for which we discuss possible reasons. The survey yielded no additional companions below or near the deuterium-burning limit, implying that their frequency at >200 AU separations is not quite as high as might be inferred from previous detections of such objects within the Sco-Cen region.

  • 59.
    Janson, Markus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Patel, Jayshil Ashokkumar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ringqvist, Simon C.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Lu, Cicero
    Rebollido, Isabel
    Lichtenberg, Tim
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Angerhausen, Daniel
    Noack, Lena
    Imaging of exocomets with infrared interferometry2023Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 671, artikkel-id A114Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Active comets have been detected in several exoplanetary systems, although so far only indirectly, when the dust or gas in the extended coma has transited in front of the stellar disk. The large optical surface and relatively high temperature of an active cometary coma also makes it suitable to study with direct imaging, but the angular separation is generally too small to be reachable with present-day facilities. However, future imaging facilities with the ability to detect terrestrial planets in the habitable zones of nearby systems will also be sensitive to exocomets in such systems. Here we examine several aspects of exocomet imaging, particularly in the context of the Large Interferometer for Exoplanets (LIFE), which is a proposed space mission for infrared imaging and spectroscopy through nulling interferometry. We study what capabilities LIFE would have for acquiring imaging and spectroscopy of exocomets, based on simulations of the LIFE performance as well as statistical properties of exocomets that have recently been deduced from transit surveys. We find that for systems with extreme cometary activities such as β Pictoris, sufficiently bright comets may be so abundant that they overcrowd the LIFE inner field of view. More nearby and moderately active systems such as є Eridani or Fomalhaut may turn out to be optimal targets. If the exocomets have strong silicate emission features, such as in comet Hale-Bopp, it may become possible to study the mineralogy of individual exocometary bodies. We also discuss the possibility of exocomets as false positives for planets, with recent deep imaging of α Centauri as one hypothetical example. Such contaminants could be common, primarily among young debris disk stars, but should be rare among the main sequence population. We discuss strategies to mitigate the risk of any such false positives.

  • 60.
    Janson, Markus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Wu, Yanqin
    Cataldi, Gianni
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Tidal disruption versus planetesimal collisions as possible origins for the dispersing dust cloud around Fomalhaut2020Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 640, artikkel-id A93Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent analysis suggests that the faint optical point source observed around Fomalhaut from 2004-2014 (Fomalhaut b) is gradually fading and expanding, supporting the case that it may be a dispersing dust cloud resulting from the sudden disruption of a planetesimal. These types of disruptions may arise from catastrophic collisions of planetesimals, which are perturbed from their original orbits in the Fomalhaut dust ring by nearby giant planets. However, disruptions can also occur when the planetesimals pass within the tidal disruption field of the planet(s) that perturbed them in the first place, similar to the Shoemaker-Levy event observed in the Solar System. Given that a gravitationally focusing giant planet has a much larger interaction cross-section than a planetesimal, tidal disruption events can match or outnumber planetesimal collision events in realistic regions of parameter space. Intriguingly, the Fomalhaut dust cloud offers an opportunity to directly distinguish between these scenarios. A tidal disruption scenario leads to a very specific prediction of ephemerides for the planet causing the event. At a most probable mass of 66 M-circle plus, a semi-major axis of 117 AU, and a system age of 400-500 Myr, this planet would be readily detectable with the James Webb Space Telescope. The presence or absence of this planet at the specific, predicted position is therefore a distinctive indicator of whether the dispersing cloud originated from a collision of two planetesimals or from the disruption of a planetesimal in the tidal field of a giant planet.

  • 61. Kiefer, F.
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Walton, N. A.
    Hint of an exocomet transit in the CHEOPS light curve of HD 1725552023Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 671, artikkel-id A25Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    HD 172555 is a young (~20 Myr) A7V star surrounded by a 10 au wide debris disk suspected to be replenished partly by collisions between large planetesimals. Small evaporating transiting bodies, that is exocomets, have also been detected in this system by spectroscopy. After β Pictoris, this is another example of a system possibly witnessing a phase of the heavy bombardment of planetesimals. In such a system, small bodies trace dynamical evolution processes. We aim to constrain their dust content by using transit photometry. We performed a 2-day-long photometric monitoring of HD 172555 with the CHEOPS space telescope in order to detect shallow transits of exocomets with a typical expected duration of a few hours. The large oscillations in the light curve indicate that HD 172555 is a δ Scuti pulsating star. After removing those dominating oscillations, we found a hint of a transient absorption. If fitted with an exocomet transit model, it would correspond to an evaporating body passing near the star at a distance of 6.8±1.4R★ (or 0.05±0.01 au) with a radius of 2.5 km. These properties are comparable to those of the exocomets already found in this system using spectroscopy, as well as those found in the β Pic system. The nuclei of the Solar System's Jupiter family comets, with radii of 2-6 km, are also comparable in size. This is the first piece of evidence of an exocomet photometric transit detection in the young system of HD 172555.

  • 62. Krivov, A. V.
    et al.
    Herrmann, F.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Thébault, Philippe
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Can gas in young debris disks be constrained by their radial brightness profiles?2009Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 507, nr 3, s. 1503-1516Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Disks around young stars are known to evolve from optically thick, gas-dominated protoplanetary disks to optically thin, almost gas-free debris disks. It is thought that the primordial gas is largely removed at ages of ~10 Myr and indeed, only little amounts of gas have been deduced from observations for debris disks at ages of ⪆10 Myr. However, gas detections are difficult and often indirect, not allowing one to discern the true gas densities. This suggests using dynamical arguments: it has been argued that gas, if present with higher densities, would lead to flatter radial profiles of the dust density and brightness than those actually observed. In this paper, we systematically study the influence of gas on the radial profiles of brightness. We assume that dust is replenished by planetesimals orbiting in a “birth ring” and model the dust distribution and scattered-light brightness profile in the outer part of the disk exterior to the birth ring, under different assumptions about the gas component. Our numerical simulations, supported with an analytic model, show that the radial profile of dust density and the surface brightness are surprisingly insensitive to variation of the parameters of a central star, location of the dust-producing planetesimal belt, dustiness of the disk and - most importantly - the parameters of the ambient gas. The radial brightness slopes in the outer disks are all typically in the range -3...-4. This result holds for a wide range of gas densities (three orders of magnitude), for different radial profiles of the gas temperature, both for gas of solar composition and gas of strongly non-solar composition. The slopes of -3...-4 we find are the same that were theoretically found for gas-free debris disks, and they are the same as actually retrieved from observations of many debris disks. Our specific results for three young (10-30 Myr old), spatially resolved, edge-on debris disks (β Pic, HD 32297, and AU Mic) show that the observed radial profiles of the surface brightness do not pose any stringent constraints on the gas component of the disk. We cannot exclude that outer parts of the systems may have retained substantial amounts of primordial gas which is not evident in the gas observations (e.g. as much as 50 Earth masses for β Pic). However, the possibility that gas, most likely secondary, is only present in little to moderate amounts, as deduced from gas detections (e.g. ~0.05 Earth masses in the β Pic disk or even less), remains open, too.

  • 63. Lacedelli, G.
    et al.
    Wilson, T. G.
    Malavolta, L.
    Hooton, M. J.
    Collier Cameron, A.
    Alibert, Y.
    Mortier, A.
    Bonfanti, A.
    Haywood, R. D.
    Hoyer, S.
    Piotto, G.
    Bekkelien, A.
    Vanderburg, A. M.
    Benz, W.
    Dumusque, X.
    Deline, A.
    Lopez-Morales, M.
    Borsato, L.
    Rice, K.
    Fossati, L.
    Latham, D. W.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Poretti, E.
    Sousa, S. G.
    Sozzetti, A.
    Salmon, S.
    Burke, C. J.
    Van Grootel, V.
    Fausnaugh, M. M.
    Adibekyan, V.
    Huang, C. X.
    Osborn, H. P.
    Mustill, A. J.
    Palle, E.
    Bourrier, V.
    Nascimbeni, V.
    Alonso, R.
    Anglada, G.
    Barczy, T.
    Barrado y Navascues, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Billot, N.
    Bonfils, X.
    Broeg, C.
    Buchhave, L. A.
    Cabrera, J.
    Charnoz, S.
    Cosentino, R.
    Csizmadia, Sz.
    Davies, M. B.
    Deleuil, M.
    Delrez, L.
    Demangeon, O.
    Demory, B.-O.
    Ehrenreich, D.
    Erikson, A.
    Esparza-Borges, E.
    Florén, Hans-Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Fortier, A.
    Fridlund, M.
    Futyan, D.
    Gandolfi, D.
    Ghedina, A.
    Gillon, M.
    Gudel, M.
    Guterman, P.
    Harutyunyan, A.
    Heng, K.
    Isaak, K. G.
    Jenkins, J. M.
    Kiss, L.
    Laskar, J.
    Lecavelier des Etangs, A.
    Lendl, M.
    Lovis, C.
    Magrin, D.
    Marafatto, L.
    Martinez Fiorenzano, A. F.
    Maxted, P. F. L.
    Mayor, M.
    Micela, G.
    Molinari, E.
    Murgas, F.
    Narita, N.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ottensamer, R.
    Pagano, I.
    Pasetti, A.
    Pedani, M.
    Pepe, F. A.
    Peter, G.
    Phillips, D. F.
    Pollacco, D.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Ratti, F.
    Rauer, H.
    Ribas, I.
    Santos, N. C.
    Sasselov, D.
    Scandariato, G.
    Seager, S.
    Segransan, D.
    Serrano, L. M.
    Simon, A. E.
    Smith, A. M. S.
    Steinberger, M.
    Steller, M.
    Szabo, Gy.
    Thomas, N.
    Twicken, J. D.
    Udry, S.
    Walton, N.
    Winn, J. N.
    Investigating the architecture and internal structure of the TOI-561 system planets with CHEOPS, HARPS-N, and TESS2022Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 511, nr 3, s. 4551-4571Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a precise characterization of the TOI-561 planetary system obtained by combining previously published data withTESS and CHEOPS photometry, and a new set of 62 HARPS-N radial velocities (RVs). Our joint analysis confirms the presenceof four transiting planets, namely TOI-561 b (P = 0.45 d, R = 1.42 R⊕, M = 2.0 M⊕), c (P = 10.78 d, R = 2.91 R⊕, M =5.4 M⊕), d (P = 25.7 d, R = 2.82 R⊕, M = 13.2 M⊕), and e (P = 77 d, R = 2.55 R⊕, M = 12.6 R⊕). Moreover, we identifyan additional, long-period signal (>450 d) in the RVs, which could be due to either an external planetary companion or tostellar magnetic activity. The precise masses and radii obtained for the four planets allowed us to conduct interior structure andatmospheric escape modelling. TOI-561 b is confirmed to be the lowest density (ρb = 3.8 ± 0.5 g cm−3) ultra-short period(USP) planet known to date, and the low metallicity of the host star makes it consistent with the general bulk density-stellarmetallicity trend. According to our interior structure modelling, planet b has basically no gas envelope, and it could host a certainamount of water. In contrast, TOI-561 c, d, and e likely retained an H/He envelope, in addition to a possibly large water layer.The inferred planetary compositions suggest different atmospheric evolutionary paths, with planets b and c having experiencedsignificant gas loss, and planets d and e showing an atmospheric content consistent with the original one. The uniqueness ofthe USP planet, the presence of the long-period planet TOI-561 e, and the complex architecture make this system an appealingtarget for follow-up studies.

  • 64. Lafreniere, David
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    A Multiplicity Census of Young Stars in Chamaeleon I2008Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We present the results of a multiplicity survey of 126 stars spanning ~0.1-3 solar masses in the ~2-Myr-old Chamaeleon I star-forming region, based on adaptive optics imaging with the ESO Very Large Telescope. Our observations have revealed 30 binaries and 6 triples, of which 19 and 4, respectively, are new discoveries. The overall multiplicity fraction we find for Cha I (~30%) is similar to those reported for other dispersed young associations, but significantly higher than seen in denser clusters and the field, for comparable samples. Both the frequency and the maximum separation of Cha I binaries decline with decreasing mass, while the mass ratios approach unity; conversely, tighter pairs are more likely to be equal mass. We confirm that brown dwarf companions to stars are rare, even at young ages at wide separations. Based on follow-up spectroscopy of two low-mass substellar companion candidates, we conclude that both are likely background stars. The overall multiplicity fraction in Cha I is in rough agreement with numerical simulations of cloud collapse and fragmentation, but its observed mass dependence is less steep than predicted. The paucity of higher-order multiples, in particular, provides a stringent constraint on the simulations, and seems to indicate a low level of turbulence in the prestellar cores in Cha I.

  • 65. Lafreniere, David
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    et al.,
    A Multiplicity Census of Young Stars in Chamaeleon I2008Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, The Astrophysical Journal, Vol. 683, nr 2, s. 844-861Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the results of a multiplicity survey of 126 stars spanning ~0.1-3 Msolar in the ~2 Myr old Chamaeleon I star-forming region, based on adaptive optics imaging with the ESO Very Large Telescope. Our observations have revealed 30 binaries and six triples, of which 19 and four, respectively, are new discoveries. The overall multiplicity fraction we find for Cha I (~30%) is similar to those reported for other dispersed young associations, but significantly higher than seen in denser clusters and the field, for comparable samples. Both the frequency and the maximum separation of Cha I binaries decline with decreasing mass, while the mass ratios approach unity; conversely, tighter pairs are more likely to be equal mass. We confirm that brown dwarf companions to stars are rare, even at young ages at wide separations. Based on follow-up spectroscopy of two low-mass substellar companion candidates, we conclude that both are likely background stars. The overall multiplicity fraction in Cha I is in rough agreement with numerical simulations of cloud collapse and fragmentation, but its observed mass dependence is less steep than predicted. The paucity of higher order multiples, in particular, provides a stringent constraint on the simulations, and seems to indicate a low level of turbulence in the prestellar cores in Cha I.

  • 66. Lafreniere, David
    et al.
    Jayawardhana, Ray
    van Kerkwijk, Marten H.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Janson, Markus
    AN ADAPTIVE OPTICS MULTIPLICITY CENSUS OF YOUNG STARS IN UPPER SCORPIUS2014Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 785, nr 1, s. 47-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the results of amultiplicity survey of 91 stars spanning masses of similar to 0.2-10M(circle dot) in the Upper Scorpius star-forming region, based on adaptive optics imaging with the Gemini North telescope. Our observations identified 29 binaries, 5 triples, and no higher order multiples. The corresponding raw multiplicity frequency is 0.37 +/- 0.05. In the regime where our observations are complete-companion separations of 0 ''.1-5 '' (similar to 15-800 AU) with magnitude limits ranging from K < 9.3 at 0 ''.1 to K < 15.8 at 5 '' -the multiplicity frequency is 0.27(-0.04.)(+ 0.05) For similar separations, the multiplicity frequency in Upper Scorpius is comparable to that in other dispersed star-forming regions, but is a factor of two to three higher than in denser star-forming regions or in the field. Our sample displays a constant multiplicity frequency as a function of stellar mass. Among our sample of binaries, we find that both wider (> 100 AU) and higher-mass systems tend to have companions with lower companion-to-primary mass ratios. Three of the companions identified in our survey are unambiguously substellar and have estimated masses below 0.04M(circle dot) (two of them are new discoveries from this survey-1RXS J160929.1-210524b and HIP 78530B-although we have reported them separately in earlier papers). These three companions have projected orbital separations of 300-900 AU. Based on a statistical analysis factoring in sensitivity limits, we calculate an occurrence rate of 5-40 M-Jup companions of similar to 4.0% for orbital separations of 250-1000 AU, compared to < 1.8% at smaller separations, suggesting that such companions are more frequent on wider orbits.

  • 67. Leleu, A.
    et al.
    Alibert, Y.
    Hara, N. C.
    Hooton, M. J.
    Wilson, T. G.
    Robutel, P.
    Delisle, J.-B.
    Laskar, J.
    Hoyer, S.
    Lovis, C.
    Bryant, E. M.
    Ducrot, E.
    Cabrera, J.
    Delrez, L.
    Acton, J. S.
    Adibekyan, V.
    Allart, R.
    Allende Prieto, C.
    Alonso, R.
    Alves, D.
    Anderson, D. R.
    Angerhausen, D.
    Anglada Escude, G.
    Asquier, J.
    Barrado, D.
    Barros, S. C. C.
    Baumjohann, W.
    Bayliss, D.
    Beck, M.
    Beck, T.
    Bekkelien, A.
    Benz, W.
    Billot, N.
    Bonfanti, A.
    Bonfils, X.
    Bouchy, F.
    Bourrier, V.
    Boue, G.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Broeg, C.
    Buder, M.
    Burdanov, A.
    Burleigh, M. R.
    Barczy, T.
    Cameron, A. C.
    Chamberlain, S.
    Charnoz, S.
    Cooke, B. F.
    Corral Van Damme, C.
    Correia, A. C. M.
    Cristiani, S.
    Damasso, M.
    Davies, M. B.
    Deleuil, M.
    Demangeon, O. D. S.
    Demory, B.-O.
    Di Marcantonio, P.
    Di Persio, G.
    Dumusque, X.
    Ehrenreich, D.
    Erikson, A.
    Figueira, P.
    Fortier, A.
    Fossati, L.
    Fridlund, M.
    Futyan, D.
    Gandolfi, D.
    Garcia Munoz, A.
    Garcia, L. J.
    Gill, S.
    Zapatero Osorio, M. R.
    Gillen, E.
    Gillon, M.
    Goad, M. R.
    Gonzalez Hernandez, J.
    Guedel, M.
    Haldemann, J.
    Henderson, B.
    Heng, K.
    Hogan, A. E.
    Isaak, K.
    Jehin, E.
    Jenkins, J. S.
    Jordan, A.
    Kiss, L.
    Kristiansen, M. H.
    Lam, K.
    Lavie, B.
    Lecavelier des Etangs, A.
    Lendl, M.
    Lillo-Box, J.
    Lo Curto, G.
    Magrin, D.
    Martins, C. J. A. P.
    Maxted, P. F. L.
    McCormac, J.
    Mehner, A.
    Micela, G.
    Molaro, P.
    Moyano, M.
    Murray, C. A.
    Nascimbeni, V.
    Nunes, N. J.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Osborn, H. P.
    Oshagh, M.
    Ottensamer, R.
    Pagano, I.
    Palle, E.
    Pedersen, P. P.
    Pepe, F. A.
    Persson, C. M.
    Peter, G.
    Piotto, G.
    Polenta, G.
    Pollacco, D.
    Poretti, E.
    Pozuelos, F. J.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Ratti, F.
    Rauer, H.
    Raynard, L.
    Rebolo, R.
    Reimers, C.
    Ribas, I.
    Santos, N. C.
    Scandariato, G.
    Schneider, J.
    Sebastian, D.
    Sestovic, M.
    Simon, A. E.
    Smith, A. M. S.
    Sousa, S. G.
    Sozzetti, A.
    Steller, M.
    Suarez Mascareno, A.
    Szabo, Gy M.
    Segransan, D.
    Thomas, N.
    Thompson, S.
    Tilbrook, R. H.
    Triaud, A.
    Turner, O.
    Udry, S.
    Van Grootel, V.
    Venus, H.
    Verrecchia, F.
    Vines, J.
    Walton, N. A.
    West, R. G.
    Wheatley, P. J.
    Wolter, D.
    Six transiting planets and a chain of Laplace resonances in TOI-1782021Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 649, artikkel-id A26Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Determining the architecture of multi-planetary systems is one of the cornerstones of understanding planet formation and evolution. Resonant systems are especially important as the fragility of their orbital configuration ensures that no significant scattering or collisional event has taken place since the earliest formation phase when the parent protoplanetary disc was still present. In this context, TOI-178 has been the subject of particular attention since the first TESS observations hinted at the possible presence of a near 2:3:3 resonant chain. Here we report the results of observations from CHEOPS, ESPRESSO, NGTS, and SPECULOOS with the aim of deciphering the peculiar orbital architecture of the system. We show that TOI-178 harbours at least six planets in the super-Earth to mini-Neptune regimes, with radii ranging from 1.152(-0.070)(+0.073)</textual-form> 1.152-0.070+0.073 to 2.87(-0.13)(+0.14)</textual-form> 2.87-0.13+0.14 Earth radii and periods of 1.91, 3.24, 6.56, 9.96, 15.23, and 20.71 days. All planets but the innermost one form a 2:4:6:9:12 chain of Laplace resonances, and the planetary densities show important variations from planet to planet, jumping from 1.02(-0.23)(+0.28)</textual-form> 1.02-0.23+0.28 to 0.177(-0.061)(+0.055)</textual-form> 0.177-0.061+0.055 times the Earth's density between planets c and d. Using Bayesian interior structure retrieval models, we show that the amount of gas in the planets does not vary in a monotonous way, contrary to what one would expect from simple formation and evolution models and unlike other known systems in a chain of Laplace resonances. The brightness of TOI-178 (H = 8.76 mag, J = 9.37 mag, V = 11.95 mag) allows for a precise characterisation of its orbital architecture as well as of the physical nature of the six presently known transiting planets it harbours. The peculiar orbital configuration and the diversity in average density among the planets in the system will enable the study of interior planetary structures and atmospheric evolution, providing important clues on the formation of super-Earths and mini-Neptunes.

  • 68. Lendl, M.
    et al.
    Csizmadia, Sz.
    Deline, A.
    Fossati, L.
    Kitzmann, D.
    Heng, K.
    Hoyer, S.
    Salmon, S.
    Benz, W.
    Broeg, C.
    Ehrenreich, D.
    Fortier, A.
    Queloz, D.
    Bonfanti, A.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Cameron, A. Collier
    Delrez, L.
    Garcia Muñoz, A.
    Hooton, M. J.
    Maxted, P. F. L.
    Morris, B. M.
    Van Grootel, V.
    Wilson, T. G.
    Alibert, Y.
    Alonso, R.
    Asquier, J.
    Bandy, T.
    Bárczy, T.
    Barrado, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Bekkelien, A.
    Bergomi, M.
    Billot, N.
    Biondi, F.
    Bonfils, X.
    Bourrier, V.
    Busch, M. -D.
    Cabrera, J.
    Cessa, V.
    Charnoz, S.
    Chazelas, B.
    Van Damme, C. Corral
    Davies, M. B.
    Deleuil, M.
    Demangeon, O. D. S.
    Demory, B. -O.
    Erikson, A.
    Farinato, J.
    Fridlund, M.
    Futyan, D.
    Gandolfi, D.
    Gillon, M.
    Guterman, P.
    Hasiba, J.
    Hernandez, E.
    Isaak, K. G.
    Kiss, L.
    Kuntzer, T.
    des Etangs, A. Lecavelier
    Lüftinger, T.
    Laskar, J.
    Lovis, C.
    Magrin, D.
    Malvasio, L.
    Marafatto, L.
    Michaelis, H.
    Munari, M.
    Nascimbeni, V.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ottacher, H.
    Ottensamer, R.
    Pagano, I.
    Pallé, E.
    Peter, G.
    Piazza, D.
    Piotto, G.
    Pollacco, D.
    Ratti, F.
    Rauer, H.
    Ragazzoni, R.
    Rando, N.
    Ribas, I.
    Rieder, M.
    Rohlfs, R.
    Safa, F.
    Santos, N. C.
    Scandariato, G.
    Ségransan, D.
    Simon, A. E.
    Singh, V.
    Smith, A. M. S.
    Sordet, M.
    Sousa, S. G.
    Steller, M.
    Szabó, Gy. M.
    Thomas, N.
    Tschentscher, M.
    Udry, S.
    Viotto, V.
    Walter, I.
    Walton, N. A.
    Wildi, F.
    Wolter, D.
    The hot dayside and asymmetric transit of WASP-189 b seen by CHEOPS2020Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 643, artikkel-id A94Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The CHEOPS space mission dedicated to exoplanet follow-up was launched in December 2019, equipped with the capacity to perform photometric measurements at the 20 ppm level. As CHEOPS carries out its observations in a broad optical passband, it can provide insights into the reflected light from exoplanets and constrain the short-wavelength thermal emission for the hottest of planets by observing occultations and phase curves. Here, we report the first CHEOPS observation of an occultation, namely, that of the hot Jupiter WASP-189 b, a MP ≈ 2MJ planet orbiting an A-type star. We detected the occultation of WASP-189 b at high significance in individual measurements and derived an occultation depth of dF = 87.9 ± 4.3 ppm based on four occultations. We compared these measurements to model predictions and we find that they are consistent with an unreflective atmosphere heated to a temperature of 3435 ± 27 K, when assuming inefficient heat redistribution. Furthermore, we present two transits of WASP-189 b observed by CHEOPS. These transits have an asymmetric shape that we attribute to gravity darkening of the host star caused by its high rotation rate. We used these measurements to refine the planetary parameters, finding a ~25% deeper transit compared to the discovery paper and updating the radius of WASP-189 b to 1.619 ± 0.021RJ. We further measured the projected orbital obliquity to be λ = 86.4−4.4+2.9°, a value that is in good agreement with a previous measurement from spectroscopic observations, and derived a true obliquity of Ψ = 85.4 ± 4.3°. Finally, we provide reference values for the photometric precision attained by the CHEOPS satellite: for the V = 6.6 mag star, and using a 1-h binning, we obtain a residual RMS between 10 and 17 ppm on the individual light curves, and 5.7 ppm when combining the four visits.

  • 69.
    Liseau, R.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Larsson, B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brandeker, A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Bergman, P.
    Bernath, P.
    Black, J. H.
    Booth, R.
    Buat, V.
    Curry, C.
    Encrenaz, P.
    Falgarone, E.
    Feldman, P.
    Fich, M.
    Florén, H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Frisk, U.
    Gerin, M.
    Gregersen, E.
    Harju, J.
    Hasegawa, T.
    Hjalmarson, Å.
    Johansson, L.
    Kwok, S.
    Lecacheux, A.
    Liljeström, T.
    Mattila, K.
    Mitchell, G.
    Nordh, L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olberg, M.
    Olofsson, G.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Pagani, L.
    Plume, R.
    Ristorcelli, I.
    Sandqvist, Aa.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Schéele, F. v.
    Serra, G.
    Tothill, N.
    Volk, K.
    Wilson, C.
    First detection of NH3 (10 -> 00) from a low mass cloud core. On the low ammonia abundance of the rho Oph A core2003Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 402, s. L73-L76Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Odin has successfully observed the molecular core rho Oph A in the 572.5 GHz rotational ground state line of ammonia, NH3 (JK = 10 -> 00). The interpretation of this result makes use of complementary molecular line data obtained from the ground (C17O and CH3OH) as part of the Odin preparatory work. Comparison of these observations with theoretical model calculations of line excitation and transfer yields a quite ordinary abundance of methanol, X(CH3OH)= 3 x 10-9. Unless NH3 is not entirely segregated from C17O and CH3OH, ammonia is found to be significantly underabundant with respect to typical dense core values, viz. X(NH3) = 8 x 10-10. Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Études Spatiales (CNES). The Swedish Space Corporation has been the industrial prime contractor. and based on observations collected with the Swedish ESO Submillimeter Telescope, SEST, in La Silla, Chile.

  • 70. Liseau, Rene
    et al.
    Risacher, Christophe
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Eiroa, Carlos
    Fridlund, Malcolm
    Nilsson, Ricky
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Pilbratt, Göran L.
    Thébault, Philippe
    q1 Eridani: a solar-type star with a planet and a dust belt2008Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 480, nr 3, s. L47-L50Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. Far-infrared excess emission from main-sequence stars is due to dust produced by orbiting minor bodies. In these disks, larger bodies, such as planets, may also be present and the understanding of their incidence and influence currently presents a challenge.

    Aims. Only very few solar-type stars exhibiting an infrared excess and harbouring planets are known to date. Indeed, merely a single case of a star-planet-disk system has previously been detected at submillimeter (submm) wavelengths. Consequently, one of our aims is to understand the reasons for these poor statistics, i.e., whether these results reflected the composition and/or the physics of the planetary disks or were simply due to observational bias and selection effects. Finding more examples would be very significant.

    Methods. The selected target, q(1) Eri, is a solar-type star, which was known to possess a planet, q(1) Eri b, and to exhibit excess emission at IRAS wavelengths, but had remained undetected in the millimeter regime. Therefore, submm flux densities would be needed to better constrain the physical characteristics of the planetary disk. Consequently, we performed submm imaging observations of q(1) Eri.

    Results. The detected dust toward q(1) Eri at 870 mu m exhibits the remarkable fact that the entire SED, from the IR to mm-wavelengths, is fit by a single-temperature blackbody function (60 K). This would imply that the emitting regions are confined to a narrow region (ring) at radial distances much larger than the orbital distance of q(1) Eri b, and that the emitting particles are considerably larger than some hundred micron. However, the 870 mu m source is extended, with a full-width-half-maximum of roughly 600AU. Therefore, a physically more compelling model also invokes a belt of cold dust (17 K), located at 300AU from the star and about 60AU wide.

    Conclusions. The minimum mass of 0.04 M-circle plus (3 M-Moon) of 1 mm-size icy ring-particles is considerable, given the stellar age of >= 1Gyr. These big grains form an inner edge at about 25 AU, which may suggest the presence of an unseen outer planet (q(1) Eri c).

  • 71. Luque, R.
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Zingales, T.
    A resonant sextuplet of sub-Neptunes transiting the bright star HD 1100672023Inngår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 623, nr 7989, s. 932-937Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Planets with radii between that of the Earth and Neptune (hereafter referred to as 'sub-Neptunes') are found in close-in orbits around more than half of all Sun-like stars. However, their composition, formation and evolution remain poorly understood3. The study of multiplanetary systems offers an opportunity to investigate the outcomes of planet formation and evolution while controlling for initial conditions and environment. Those in resonance (with their orbital periods related by a ratio of small integers) are particularly valuable because they imply a system architecture practically unchanged since its birth. Here we present the observations of six transiting planets around the bright nearby star HD 110067. We find that the planets follow a chain of resonant orbits. A dynamical study of the innermost planet triplet allowed the prediction and later confirmation of the orbits of the rest of the planets in the system. The six planets are found to be sub-Neptunes with radii ranging from 1.94R⊕ to 2.85R⊕. Three of the planets have measured masses, yielding low bulk densities that suggest the presence of large hydrogen-dominated atmospheres.

  • 72. Malbet, Fabien
    et al.
    Boehm, Celine
    Krone-Martins, Alberto
    Amorim, Antonio
    Anglada-Escude, Guillem
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Courbin, Frederic
    Ensslin, Torsten
    Falcao, Antonio
    Freese, Katherine
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. University of Texas, USA.
    Holl, Berry
    Labadie, Lucas
    Leger, Alain
    Mamon, Gary A.
    McArthur, Barbara
    Mora, Alcione
    Shao, Mike
    Sozzetti, Alessandro
    Spolyar, Douglas
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Villaver, Eva
    Abbas, Ummi
    Albertus, Conrado
    Alves, Joao
    Barnes, Rory
    Bonomo, Aldo Stefano
    Bouy, Herve
    Brown, Warren R.
    Cardoso, Vitor
    Castellani, Marco
    Chemin, Laurent
    Clark, Hamish
    Correia, Alexandre C. M.
    Crosta, Mariateresa
    Crouzier, Antoine
    Damasso, Mario
    Darling, Jeremy
    Davies, Melvyn B.
    Diaferio, Antonaldo
    Fortin, Morgane
    Fridlund, Malcolm
    Gai, Mario
    Garcia, Paulo
    Gnedin, Oleg
    Goobar, Ariel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Gordo, Paulo
    Goullioud, Renaud
    Hall, David
    Hambly, Nigel
    Harrison, Diana
    Hobbs, David
    Holland, Andrew
    Hog, Erik
    Jordi, Carme
    Klioner, Sergei
    Lancon, Ariane
    Laskar, Jacques
    Lattanzi, Mario
    Le Poncin-Lafitte, Christophe
    Luri, Xavier
    Michalik, Daniel
    Moitinho de Almeida, Andre
    Mourao, Ana
    Moustakas, Leonidas
    Murray, Neil J.
    Muterspaugh, Matthew
    Oertel, Micaela
    Ostorero, Luisa
    Portell, Jordi
    Prost, Jean-Pierre
    Quirrenbach, Andreas
    Schneider, Jean
    Scott, Pat
    Siebert, Arnaud
    da Silva, Antonio
    Silva, Manuel
    Thebault, Philippe
    Tomsick, John
    Traub, Wesley
    de Val-Borro, Miguel
    Valluri, Monica
    Walton, Nicholas A.
    Watkins, Laura L.
    White, Glenn
    Wyrzykowski, Lukasz
    Wyse, Rosemary
    Yamada, Yoshiyuki
    Faint objects in motion: the new frontier of high precision astrometry2021Inngår i: Experimental astronomy, ISSN 0922-6435, E-ISSN 1572-9508, Vol. 51, s. 845-886Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sky survey telescopes and powerful targeted telescopes play complementary roles in astronomy. In order to investigate the nature and characteristics of the motions of very faint objects, a flexibly-pointed instrument capable of high astrometric accuracy is an ideal complement to current astrometric surveys and a unique tool for precision astrophysics. Such a space-based mission will push the frontier of precision astrometry from evidence of Earth-mass habitable worlds around the nearest stars, to distant Milky Way objects, and out to the Local Group of galaxies. As we enter the era of the James Webb Space Telescope and the new ground-based, adaptive-optics-enabled giant telescopes, by obtaining these high precision measurements on key objects that Gaia could not reach, a mission that focuses on high precision astrometry science can consolidate our theoretical understanding of the local Universe, enable extrapolation of physical processes to remote redshifts, and derive a much more consistent picture of cosmological evolution and the likely fate of our cosmos. Already several missions have been proposed to address the science case of faint objects in motion using high precision astrometry missions: NEAT proposed for the ESA M3 opportunity, micro-NEAT for the S1 opportunity, and Theia for the M4 and M5 opportunities. Additional new mission configurations adapted with technological innovations could be envisioned to pursue accurate measurements of these extremely small motions. The goal of this White Paper is to address the fundamental science questions that are at stake when we focus on the motions of faint sky objects and to briefly review instrumentation and mission profiles.

  • 73. Matthews, Brenda C.
    et al.
    Kennedy, Grant
    Sibthorpe, Bruce
    Holland, Wayne
    Booth, Mark
    Kalas, Paul
    MacGregor, Meredith
    Wilner, David
    Vandenbussche, Bart
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Blommaert, Joris
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Dent, W. R. F.
    de Vries, Bernard L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Di Francesco, James
    Fridlund, Malcolm
    Graham, James R.
    Greaves, Jane
    Heras, Ana M.
    Hogerheijde, Michiel
    Ivison, R. J.
    Pantin, Eric
    Pilbratt, Goran L.
    THE AU MIC DEBRIS DISK: FAR-INFRARED AND SUBMILLIMETER RESOLVED IMAGING2015Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 811, nr 2, artikkel-id 100Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present far-infrared and submillimeter maps from the Herschel Space Observatory and the James Clerk Maxwell Telescope of the debris disk host star AU Microscopii. Disk emission is detected at 70, 160, 250, 350, 450, 500, and 850 mu m. The disk is resolved at 70, 160, and 450 mu m. In addition to the planetesimal belt, we detect thermal emission from AU Mic's halo for the first time. In contrast to the scattered light images, no asymmetries are evident in the disk. The fractional luminosity of the disk is 3.9 x 10(-4) and its milimeter-grain dust mass is 0.01 M-circle dot (+/- 20%). We create a simple spatial model that reconciles the disk spectral energy distribution as a blackbody of 53 +/- 2K (a composite of 39 and 50 K components) and the presence of small (non-blackbody) grains which populate the extended halo. The best-fit model is consistent with the birth ring model explored in earlier works, i.e., an edge-on dust belt extending from 8.8 to 40 AU, but with an additional halo component with an r(-1.5) surface density profile extending to the limits of sensitivity (140 AU). We confirm that AU Mic does not exert enough radiation force to blow out grains. For stellar mass-loss rates of 10-100 times solar, compact (zero porosity) grains can only be removed if they are very small; consistently with previous work, if the porosity is 0.9, then grains approaching 0.1 mu m can be removed via corpuscular forces (i.e., the stellar wind).

  • 74. Maxted, P. F. L.
    et al.
    Ehrenreich, D.
    Wilson, T. G.
    Alibert, Y.
    Collier Cameron, A.
    Hoyer, S.
    Sousa, S. G.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Bekkelien, A.
    Deline, A.
    Delrez, L.
    Bonfanti, A.
    Borsato, L.
    Alonso, R.
    Anglada Escudé, G.
    Barrado, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Benz, W.
    Billot, N.
    Biondi, F.
    Bonfils, X.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Broeg, C.
    Bárczy, T.
    Cabrera, J.
    Charnoz, S.
    Corral Van Damme, C.
    Csizmadia, Sz
    Davies, M. B.
    Deleuil, M.
    Demangeon, O. D. S.
    Demory, B.-O.
    Erikson, A.
    Florén, Hans Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Fortier, A.
    Fossati, L.
    Fridlund, M.
    Futyan, D.
    Gandolfi, D.
    Gillon, M.
    Guedel, M.
    Guterman, P.
    Heng, K.
    Isaak, K. G.
    Kiss, L.
    Laskar, J.
    Lecavelier des Etangs, A.
    Lendl, M.
    Lovis, C.
    Magrin, D.
    Nascimbeni, V.
    Ottensamer, R.
    Pagano, I.
    Pallé, E.
    Peter, G.
    Piotto, G.
    Pollacco, D.
    Pozuelos, F. J.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Rauer, H.
    Reimers, C.
    Ribas, I.
    Salmon, S.
    Santos, N. C.
    Scandariato, G.
    Simon, A. E.
    Smith, A. M. S.
    Steller, M.
    Swayne, M.
    Szabó, Gy. M.
    Ségransan, D.
    Thomas, N.
    Udry, S.
    Van Grootel, V.
    Walton, N. A.
    Analysis of Early Science observations with the CHaracterising ExOPlanets Satellite (CHEOPS) using pycheops2022Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 514, nr 1, s. 77-104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    CHEOPS (CHaracterising ExOPlanet Satellite) is an ESA S-class mission that observes bright stars at high cadence from low-Earth orbit. The main aim of the mission is to characterize exoplanets that transit nearby stars using ultrahigh precision photometry. Here, we report the analysis of transits observed by CHEOPS during its Early Science observing programme for four well-known exoplanets: GJ 436 b, HD 106315 b, HD 97658 b, and GJ 1132 b. The analysis is done using pycheops, an open-source software package we have developed to easily and efficiently analyse CHEOPS light-curve data using state-of-the-art techniques that are fully described herein. We show that the precision of the transit parameters measured using CHEOPS is comparable to that from larger space telescopes such as Spitzer Space Telescope and Kepler. We use the updated planet parameters from our analysis to derive new constraints on the internal structure of these four exoplanets.

  • 75. Maxted, P. F. L.
    et al.
    Miller, N. J.
    Hoyer, S.
    Adibekyan, V.
    Sousa, S. G.
    Billot, N.
    Fortier, A.
    Simon, A. E.
    Collier Cameron, A.
    Swayne, M.
    Gutermann, P.
    Triaud, A. H. M. J.
    Southworth, J.
    Alibert, Y.
    Alonso, R.
    Anglada, G.
    Bárczy, T.
    Barrado Navascues, D.
    Barros, S. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Benz, W.
    Bonfils, X.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Broeg, C.
    Buder, M.
    Cabrera, J.
    Charnoz, S.
    Corral van Damme, C.
    Csizmadia, Sz.
    Davies, M. B.
    Deleuil, M.
    Delrez, L.
    Demangeon, O.
    Demory, B.-O.
    Ehrenreich, D.
    Erikson, A.
    Fossati, L.
    Fridlund, M.
    Gandolfi, D.
    Gillon, M.
    Güdel, M.
    Heng, K.
    Hernández Leon, J. E.
    Isaak, K. G.
    Kiss, L. L.
    Laskar, J.
    Lecavelier des Etangs, A.
    Lendl, M.
    Lovis, C.
    Magrin, D.
    Munari, M.
    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.
    Van Grootel, V.
    Walton, N.
    Fundamental effective temperature measurements for eclipsing binary stars - III. SPIRou near-infrared spectroscopy and CHEOPS photometry of the benchmark G0V star EBLM J0113+312022Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 513, nr 4, s. 6042-6057Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    EBLM J0113+31 is a moderately bright (V = 10.1), metal-poor ([Fe/H] ≈−0.3) G0V star with a much fainter M dwarf companion on a wide, eccentric orbit (= 14.3 d). We have used near-infrared spectroscopy obtained with the SPIRou spectrograph to measure the semi-amplitude of the M dwarf’s spectroscopic orbit, and high-precision photometry of the eclipse and transit from the CHEOPS and TESS space missions to measure the geometry of this binary system. From the combined analysis of these data together with previously published observations, we obtain the following model-independent masses and radii: M1 = 1.029 ± 0.025 M⊙, M2 = 0.197 ± 0.003 M⊙, R1 = 1.417 ± 0.014 R⊙, R2 = 0.215 ± 0.002 R⊙. Using R1 and the parallax from Gaia EDR3 we find that this star’s angular diameter is θ = 0.0745 ± 0.0007 mas. The apparent bolometric flux of the G0V star corrected for both extinction and the contribution from the M dwarf (<0.2 per cent) is F⊕,0=(2.62±0.05)×10−9F⊕,0=(2.62±0.05)×10−9 erg cm−2 s−1. Hence, this G0V star has an effective temperature Teff,1=6124K±40K(rnd.)±10K(sys.)Teff,1=6124K±40K(rnd.)±10K(sys.)⁠. EBLM J0113+31 is an ideal benchmark star that can be used for ‘end-to-end’ tests of the stellar parameters measured by large-scale spectroscopic surveys, or stellar parameters derived from asteroseismology with PLATO. The techniques developed here can be applied to many other eclipsing binaries in order to create a network of such benchmark stars.

  • 76. Mentuch, Erin
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    et al.,
    Lithium Depletion of Nearby Young Stellar Associations2008Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We estimate cluster ages from lithium depletion in five pre-main-sequence groups found within 100 pc of the Sun: TW Hydrae Association, Eta Chamaeleontis Cluster, Beta Pictoris Moving Group, Tucanae-Horologium Association and AB Doradus Moving Group. We determine surface gravities, effective temperatures and lithium abundances for over 900 spectra through least squares fitting to model-atmosphere spectra. For each group, we compare the dependence of lithium abundance on temperature with isochrones from pre-main-sequence evolutionary tracks to obtain model dependent ages. We find that the Eta Chamaelontis Cluster and the TW Hydrae Association are the youngest, with ages of 12+/-6 Myr and 12+/-8 Myr, respectively, followed by the Beta Pictoris Moving Group at 21+/-9 Myr, the Tucanae-Horologium Association at 27+/-11 Myr, and the AB Doradus Moving Group at an age of at least 45 Myr (where we can only set a lower limit since the models -- unlike real stars -- do not show much lithium depletion beyond this age). Here, the ordering is robust, but the precise ages depend on our choice of both atmospheric and evolutionary models. As a result, while our ages are consistent with estimates based on Hertzsprung-Russell isochrone fitting and dynamical expansion, they are not yet more precise. Our observations do show that with improved models, much stronger constraints should be feasible: the intrinsic uncertainties, as measured from the scatter between measurements from different spectra of the same star, are very low: around 10 K in effective temperature, 0.05 dex in surface gravity, and 0.03 dex in lithium abundance.

  • 77. Mentuch, Erin
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    van Kerkwijk, Marten H.
    Jayawardhana, Ray
    Hauschildt, Peter H.
    Lithium Depletion of Nearby Young Stellar Associations2008Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 689, s. 1127-1140Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We estimate cluster ages from lithium depletion in five pre-main-sequence groups found within 100 pc of the Sun: the TW Hydrae association, η Chamaeleontis cluster, β Pictoris moving group, Tucanae-Horologium association, and AB Doradus moving group. We determine surface gravities, effective temperatures, and lithium abundances for over 900 spectra through least-squares fitting to model-atmosphere spectra. For each group, we compare the dependence of lithium abundance on temperature with isochrones from pre-main-sequence evolutionary tracks to obtain model-dependent ages. We find that the η Cha cluster and the TW Hydrae association are the youngest, with ages of 12+/-6 Myr and 12+/-8 Myr, respectively, followed by the β Pic moving group at 21+/-9 Myr, the Tucanae-Horologium association at 27+/-11 Myr, and the AB Dor moving group at an age of at least 45 Myr (whereby we can only set a lower limit, since the models-unlike real stars-do not show much lithium depletion beyond this age). Here the ordering is robust, but the precise ages depend on our choice of both atmospheric and evolutionary models. As a result, while our ages are consistent with estimates based on Hertzsprung-Russell isochrone fitting and dynamical expansion, they are not yet more precise. Our observations do show that with improved models, much stronger constraints should be feasible, as the intrinsic uncertainties, as measured from the scatter between measurements from different spectra of the same star, are very low: around 10 K in effective temperature, 0.05 dex in surface gravity, and 0.03 dex in lithium abundance.

  • 78. Morgado, B. E.
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Florén, Hans Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    de Wit, J.
    A dense ring of the trans-Neptunian object Quaoar outside its Roche limit2023Inngår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 614, nr 7947, s. 239-243Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In our efforts to characterize Quaoar’s shape and search for putative material around it, we have predicted and observed several stellar occultations by this body. Following a report from Australia of a Neptune-like ring detected during a 2021 occultation and independently suspected in 2019, we have identified secondary events in previous occultations observed between 2018 and 2020. They are consistent with a circular ring centred on the body, with two possible mirror solutions for the ring orientation. Both solutions have radii close to 4,100 km, or roughly 7.4 Quaoar radii. One solution has a ring pole that presents a large mismatch with Weywot’s orbital pole, whereas the other solution is consistent with a ring coplanar with Weywot’s orbit. This is our preferred solution, as a primordial collisional system surrounding Quaoar is expected to settle in a disc that subsequently forms both the ring and Weywot.

  • 79. Morgado, B. E.
    et al.
    Bruno, G.
    Gomes-Júnior, A. R.
    Pagano, I
    Sicardy, B.
    Fortier, A.
    Desmars, J.
    Maxted, P. F. L.
    Braga-Ribas, F.
    Queloz, D.
    Sousa, S. G.
    Ortiz, J. L.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Cameron, A. Collier
    Pereira, C. L.
    Florén, Hans Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Hara, N.
    Souami, D.
    Isaak, K. G.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholm Univ, Alballova Univ Ctr, Dept Astron, S-10691 Stockholm, Sweden.
    Santos-Sanz, P.
    Wilson, T. G.
    Broughton, J.
    Alibert, Y.
    Alonso, R.
    Anglada, G.
    Bárczy, T.
    Barrado, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Benz, W.
    Billot, N.
    Bonfils, X.
    Broeg, C.
    Cabrera, J.
    Charnoz, S.
    Csizmadia, S.
    Davies, M. B.
    Deleuil, M.
    Delrez, L.
    Demangeon, O. D. S.
    Demory, B. O.
    Ehrenreich, D.
    Erikson, A.
    Fossati, L.
    Fridlund, M.
    Gandolfi, D.
    Gillon, M.
    Güdel, M.
    Heng, K.
    Hoyer, S.
    Kiss, L. L.
    Laskar, J.
    des Etangs, A. Lecavelier
    Lendl, M.
    Lovis, C.
    Magrin, D.
    Marafatto, L.
    Nascimbeni, V
    Ottensamer, R.
    Pallé, E.
    Peter, G.
    Piazza, D.
    Piotto, G.
    Pollacco, D.
    Ragazzoni, R.
    Rando, N.
    Ratti, F.
    Rauer, H.
    Reimers, C.
    Ribas, I
    Santos, N. C.
    Scandariato, G.
    Ségransan, D.
    Simon, A. E.
    Smith, A. M. S.
    Steller, M.
    Szabó, G. M.
    Thomas, N.
    Udry, S.
    Van Grootel, V.
    Walton, N. A.
    Westerdorff, K.
    A stellar occultation by the transneptunian object (50000) Quaoar observed by CHEOPS2022Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 664, artikkel-id L15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. Stellar occultation is a powerful technique that allows the determination of some physical parameters of the occulting object. The result depends on the photometric accuracy, the temporal resolution, and the number of chords obtained. Space telescopes can achieve high photometric accuracy as they are not affected by atmospheric scintillation.

    Aims. Using ESA’s CHEOPS space telescope, we observed a stellar occultation by the transneptunian object (50000) Quaoar. We compare the obtained chord with previous occultations by this object and determine its astrometry with sub-milliarcsecond precision. Also, we determine upper limits to the presence of a global methane atmosphere on the occulting body.

    Methods. We predicted and observed a stellar occultation by Quaoar using the CHEOPS space telescope. We measured the occultation light curve from this dataset and determined the dis- and reappearance of the star behind the occulting body. Furthermore, a ground-based telescope in Australia was used to constrain Quaoar’s limb. Combined with results from previous works, these measurements allowed us to obtain a precise position of Quaoar at the occultation time.

    Results. We present the results obtained from the first stellar occultation by a transneptunian object using a space telescope orbiting Earth; it was the occultation by Quaoar observed on 2020 June 11. We used the CHEOPS light curve to obtain a surface pressure upper limit of 85 nbar for the detection of a global methane atmosphere. Also, combining this observation with a ground-based observation, we fitted Quaoar’s limb to determine its astrometric position with an uncertainty below 1.0 mas.

    Conclusions. This observation is the first of its kind, and it shall be considered as a proof of concept of stellar occultation observations of transneptunian objects with space telescopes orbiting Earth. Moreover, it shows significant prospects for the James Webb Space Telescope.

  • 80. Morris, B. M.
    et al.
    Delrez, L.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Cameron, A. C.
    Simon, A. E.
    Futyan, D.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Hoyer, S.
    Fortier, A.
    Demory, B-O
    Lendl, M.
    Wilson, T. G.
    Oshagh, M.
    Heng, K.
    Ehrenreich, D.
    Sulis, S.
    Alibert, Y.
    Alonso, R.
    Anglada Escudé, G.
    Barrado, D.
    Barros, S. C. C.
    Baumjohann, W.
    Beck, M.
    Beck, T.
    Bekkelien, A.
    Benz, W.
    Bergomi, M.
    Billot, N.
    Bonfils, X.
    Bourrier, V
    Broeg, C.
    Barczy, T.
    Cabrera, J.
    Charnoz, S.
    Davies, M. B.
    De Miguel Ferreras, D.
    Deleuil, M.
    Deline, A.
    Demangeon, O. D. S.
    Erikson, A.
    Florén, Hans Gustav Axel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Fossati, L.
    Fridlund, M.
    Gandolfi, D.
    Muñoz, A. García
    Gillon, M.
    Guedel, M.
    Guterman, P.
    Isaak, K.
    Kiss, L.
    Laskar, J.
    des Etangs, A. Lecavelier
    Lieder, M.
    Lovis, C.
    Magrin, D.
    Maxted, P. F. L.
    Nascimbeni, V
    Ottensamer, R.
    Pagano, I
    Pallé, E.
    Peter, G.
    Piotto, G.
    Pizarro Rubio, A.
    Pollacco, D.
    Pozuelos, F. J.
    Queloz, D.
    Ragazzoni, R.
    Rando, N.
    Rauer, H.
    Ribas, I
    Santos, N. C.
    Scandariato, G.
    Smith, A. M. S.
    Sousa, S. G.
    Steller, M.
    Szabó, Gy M.
    Ségransan, D.
    Thomas, N.
    Udry, S.
    Ulmer, B.
    Van Grootel, V.
    Walton, N. A.
    CHEOPS precision phase curve of the Super-Earth 55 Cancri e2021Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 653, artikkel-id A173Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. 55 Cnc e is a transiting super-Earth (radius 1.88 R and mass 8 M) orbiting a G8V host star on a 17-h orbit. Spitzer observations of the planet’s phase curve at 4.5 μm revealed a time-varying occultation depth, and MOST optical observations are consistent with a time-varying phase curve amplitude and phase offset of maximum light. Both broadband and high-resolution spectroscopic analyses are consistent with either a high mean molecular weight atmosphere or no atmosphere for planet e. A long-term photometric monitoring campaign on an independent optical telescope is needed to probe the variability in this system.

    Aims. We seek to measure the phase variations of 55 Cnc e with a broadband optical filter with the 30 cm effective aperture space telescope CHEOPS and explore how the precision photometry narrows down the range of possible scenarios.

    Methods. We observed 55 Cnc for 1.6 orbital phases in March of 2020. We designed a phase curve detrending toolkit for CHEOPS photometry which allowed us to study the underlying flux variations in the 55 Cnc system.

    Results. We detected a phase variation with a full-amplitude of 72 ± 7 ppm, but did not detect a significant secondary eclipse of the planet. The shape of the phase variation resembles that of a piecewise-Lambertian; however, the non-detection of the planetary secondary eclipse, and the large amplitude of the variations exclude reflection from the planetary surface as a possible origin of the observed phase variations. They are also likely incompatible with magnetospheric interactions between the star and planet, but may imply that circumplanetary or circumstellar material modulate the flux of the system.

    Conclusions. This year, further precision photometry of 55 Cnc from CHEOPS will measure variations in the phase curve amplitude and shape over time.

  • 81. Morris, Brett M.
    et al.
    Heng, Kevin
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Swan, Andrew
    Lendl, Monika
    A CHEOPS white dwarf transit search2021Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 651, artikkel-id L12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    White dwarf spectroscopy shows that nearly half of white dwarf atmospheres contain metals that must have been accreted from planetary material that survived the red giant phases of stellar evolution. We can use metal pollution in white dwarf atmospheres as flags, signalling recent accretion, in order to prioritize an efficient sample of white dwarfs to search for transiting material. We present a search for planetesimals orbiting six nearby white dwarfs with the CHaracterising ExOPlanet Satellite (CHEOPS). The targets are relatively faint for CHEOPS, 11 mag<G<12.8 mag. We used aperture photometry data products from the CHEOPS mission as well as custom point-spread function photometry to search for periodic variations in flux due to transiting planetesimals. We detect no significant variations in flux that cannot be attributed to spacecraft systematics, despite reaching a photometric precision of < 2 ppt in 60 s exposures on each target. We simulate observations to show that the small survey is sensitive primarily to Moon-sized transiting objects with periods between 3 h<P<10 h, with radii of R<greater than or similar to>1000 km.

  • 82. Nguyen, Duy
    et al.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    A Search for Disk-Locking in the Chamaeleon I Star Forming Region2008Inngår i: Precision Spectroscopy in Astrophysics, 2008Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    We investigated the connection between disks and stellar rotation. Disk-locking theory predicts that accreting stars are preferentially slow rotators compared to their peers. If true, classical T Tauri stars (CTTS), which are accreting based on strong Hα, emission, should have observably lower vsini, values compared to weak-lined T Tauri stars (WTTS), which are not accreting. We present our findings from high-resolution optical spectra taken with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph on the Magellan Clay 6.5-m telescope located at the Las Campanas Observatory of 63 T Tauri stars in the Cha I SFR.

  • 83. Nguyen, Duy Cuong
    et al.