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  • 1.
    Asensio Torres, Ruben
    Stockholm University, Faculty of Science, Department of Astronomy.
    High-contrast imaging of low-mass companions and debris disks2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The search for exoplanets, i.e., planets orbiting other stars than the Sun, is a relatively new research field, but has already established itself as one of the most prolific and intriguing areas of astronomy. By now we are in a situation where the focus is not only on finding companions to stars, but also on characterising their atmospheres and physical properties, which overall allows us to put our Solar System into context. In the near future, these efforts could potentially lead to the first confirmation of a life-bearing planet besides the Earth. 

    The great majority of these exoplanet studies have been carried out indirectly, where the presence and characterisation of the companions are inferred solely from the observation of the host star. In the last decade, however, high-contrast direct imaging has been continuously developed to get rid of the starlight and reveal the existence of low-mass companions. Although this technique is currently limited to giant planets orbiting at large separations, it is able to directly detect the light emitted or scattered off the planet’s atmosphere at high signal to noise, which makes it the most promising planet-hunting method to characterise new worlds. Moreover, its capability to image faint objects close to the parent star allows for not only the detection of planetary-mass companions, but also low-mass stars, brown dwarfs, and circumstellar disks where planet formation takes place. This opens up a broad range of science cases where direct observations can be used to understand planet formation, atmospheric physics and stellar evolution.      

    In this PhD thesis I provide an up-to-date introduction to the basis of the direct imaging technique, and explain the star and planet formation mechanisms. Three publications are attached to this introduction, each of them dealing with distinct science cases that can be  assessed with high-contrast observations. In Paper I we resolve and model the aftermath of star formation, the so-called debris disk phase analogue to the asteroid and Kuiper belts in our Solar System, around the HD 32297 star with Subaru/HiCIAO.  We reveal an edge-on disk and find the first indications of a double-ring scenario. We also present the first polarimetric study of this system, constraining the properties of the dust around the star.  In Paper II we focus on the planetary-mass regime, and conduct the first direct imaging survey searching for circumbinary planets orbiting tight binary systems (SPOTS: Search for Planets Orbiting Two Stars). We present the results of the observations of 62 targets with VLT/NaCo and VLT/SPHERE, and perform a statistical analysis on the findings, placing constraints on the population of giant planets and brown dwarfs on wide orbits. Finally, in Paper III we resolve a triple stellar system with the newly-commissioned SCExAO/CHARIS integral field spectrograph. Taking advantage of the coeval nature of the system and the different range of masses involved, we use the data to reaffirm a previously suggested isochronal age discrepancy between the low- and the intermediate-mass population of stars.

  • 2.
    Asensio-Torres, Ruben
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bonavita, M.
    Desidera, S.
    Thalmann, C.
    Kuzuhara, M.
    Henning, Th.
    Marzari, F.
    Meyer, M. R.
    Calissendorff, Per
    Stockholm University, Faculty of Science, Department of Astronomy.
    Uyama, T.
    SPOTS: The Search for Planets Orbiting Two Stars III. Complete sample and statistical analysis2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 619, article id A43Article in journal (Refereed)
    Abstract [en]

    Binary stars constitute a large percentage of the stellar population, yet relatively little is known about the planetary systems orbiting them. Most constraints on circumbinary planets (CBPs) so far come from transit observations with the Kepler telescope, which is sensitive to close-in exoplanets but does not constrain planets on wider orbits. However, with continuous developments in high-contrast imaging techniques, this population can now be addressed through direct imaging. We present the full survey results of the Search for Planets Orbiting Two Stars (SPOTS) survey, which is the first direct imaging survey targeting CBPs. The SPOTS observational program comprises 62 tight binaries that are young and nearby, and thus suitable for direct imaging studies, with VLT/NaCo and VLT/SPHERE. Results from SPOTS include the resolved circumbinary disk around AK Sco, the discovery of a low-mass stellar companion in a triple packed system, the relative astrometry of up to 9 resolved binaries, and possible indications of non-background planetary-mass candidates around HIP 77911. We did not find any CBP within 300 AU, which implies a frequency upper limit on CBPs (1-15 M-Jup) of 6-10% between 30-300 AU. Coupling these observations with an archival dataset for a total of 163 stellar pairs, we find a best-fit CBP frequency of 1.9% (2-15 M-Jup) between 1 and 300 AU with a 10.5% upper limit at a 95% confidence level. This result is consistent with the distribution of companions around single stars.

  • 3.
    Asensio-Torres, Ruben
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Hashimoto, J.
    Thalmann, C.
    Currie, T.
    Buenzli, E.
    Kudo, T.
    Kuzuhara, M.
    Kusakabe, N.
    Abe, L.
    Akiyama, E.
    Brandner, W.
    Brandt, T. D.
    Carson, J.
    Egner, S.
    Feldt, M.
    Goto, M.
    Grady, C.
    Guyon, O.
    Hayano, Y.
    Hayashi, M.
    Hayashi, S.
    Henning, T.
    Hodapp, K.
    Ishii, M.
    Iye, M.
    Kandori, R.
    Knapp, G.
    Kwon, J.
    Matsuo, T.
    McElwain, M.
    Mayama, S.
    Miyama, S.
    Morino, J.
    Moro-Martin, A.
    Nishimura, T.
    Pyo, T.
    Serabyn, E.
    Suenaga, T.
    Suto, H.
    Suzuki, R.
    Takahashi, Y.
    Takami, M.
    Takato, N.
    Terada, H.
    Turner, E.
    Watanabe, M.
    Wisniewski, J.
    Yamada, T.
    Takami, H.
    Usuda, T.
    Tamura, M.
    Polarimetry and flux distribution in the debris disk around HD 322972016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 593, article id A73Article in journal (Refereed)
    Abstract [en]

    We present high-contrast angular differential imaging (ADI) observations of the debris disk around HD32297 in H-band, as well as the first polarimetric images for this system in polarized differential imaging (PDI) mode with Subaru/HICIAO. In ADI, we detect the nearly edge-on disk at > 5 sigma levels from similar to 0.45 '' to similar to 1.7 '' (50-192AU) from the star and recover the spine deviation from the midplane already found in previous works. We also find for the first time imaging and surface brightness (SB) indications for the presence of a gapped structure on both sides of the disk at distances of similar to 0.75 '' (NE side) and similar to 0.65 '' (SW side). Global forward-modelling work delivers a best-fit model disk and well-fitting parameter intervals that essentially match previous results, with high-forward scattering grains and a ring located at 110AU. However, this single ring model cannot account for the gapped structure seen in our SB profiles. We create simple double ring models and achieve a satisfactory fit with two rings located at 60 and 95AU, respectively, low-forward scattering grains and very sharp inner slopes. In polarized light we retrieve the disk extending from similar to 0.25-1.6 '', although the central region is quite noisy and high S/N are only found in the range similar to 0.75-1.2 ''. The disk is polarized in the azimuthal direction, as expected, and the departure from the midplane is also clearly observed. Evidence for a gapped scenario is not found in the PDI data. We obtain a linear polarization degree of the grains that increases from similar to 10% at 0.55 '' to similar to 25% at 1.6 ''. The maximum is found at scattering angles of similar to 90 degrees, either from the main components of the disk or from dust grains blown out to larger radii.

  • 4.
    Asensio-Torres, Ruben
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Tamura, Motohide
    Isochronal age-mass discrepancy of young stars: SCExAO/CHARIS integral field spectroscopy of the HIP 79124 triple system2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 622, article id A42Article in journal (Refereed)
    Abstract [en]

    We present SCExAO/CHARIS 1.1--2.4 micron integral field direct spectroscopy of the young HIP 79124 triple system. HIP 79124 is a member of the Scorpius-Centaurus association, consisting of an A0V primary with two low-mass companions at a projected separation of <1 arcsecond. Thanks to the high quality wavefront corrections provided by SCExAO, both companions are decisively detected without the employment of any PSF-subtraction algorithm to eliminate quasi-static noise. The spectrum of the outer C object is very well matched by Upper Scorpius M4 pm 0.5 standard spectra, with a Teff = 2945 pm 100 and a mass of 350 MJup. HIP 79124 B is detected at a separation of only 180 mas in a highly-correlated noise regime, and it falls in the spectral range M6 pm 0.5 with Teff = 2840 pm 190 and 100 MJup. Previous studies of stellar populations in Sco-Cen have highlighted a discrepancy in isochronal ages between the lower-mass and higher-mass populations. This could be explained either by an age spread in the region, or by conventional isochronal models failing to reproduce the evolution of low-mass stars. The HIP 79124 system should be coeval, and therefore it provides an ideal laboratory to test these scenarios. We place the three components in a color-magnitude diagram and find that the models predict a younger age for the two low-mass companions (3 Myr) than for the primary star (6 Myr). These results imply that the omission of magnetic effects in conventional isochronal models inhibit them from reproducing early low-mass stellar evolution, which is further supported by the fact that new models that include such effects provide more consistent ages in the HIP 79124 system.

  • 5.
    Calissendorff, Per
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Asensio-Torres, Ruben
    Stockholm University, Faculty of Science, Department of Astronomy.
    Koehler, Rainer
    Spectral characterization of newly detected young substellar binaries with SINFONI2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 627, article id A167Article in journal (Refereed)
    Abstract [en]

    We observe 14 young low-mass substellar objects using the VLT/SINFONI integral field spectrograph with laser guide star adaptive optics to detect and characterize three candidate binary systems. All three binary candidates show strong signs of youth, with two of them likely belonging to young moving groups. Together with the adopted young-moving-group ages we employ isochrones from the BT-Settle CIFIST substellar evolutionary models to estimate individual masses for the binary components. We find 2MASS J15104786-2818174 to be part of the approximate to 30-50 Myr Argus moving group and to be composed of a 34-48 M-Jup primary brown dwarf with spectral type M9 gamma and a fainter 15 22 MJup companion, separated by approximate to 100 mas. 2MASS J22025794-5605087 is identified as an almost equal-mass binary in the AB Dor moving group, with a projected separation of approximate to 60 mas. Both components share spectral type M9 gamma/beta, which with the adopted age of 120 200 Myr yields masses in the range of 50 68 M-Jup for each component individually. The observations of 2MASS J15474719-2423493 are of lower quality and we obtain no spectral characterization for the target, but resolve two components separated by approximate to 170 mas which with the predicted young field age of 30 50 Myr yields individual masses below 20 M-Jup. Out of the three candidate binary systems, 2MASS J22025794-5605087 has unambiguous spectroscopic signs of being a bona-fide binary, while the other two will require second-epoch confirmation. The small projected separations between the binary components correspond to physical separations of approximate to 4-7AU, meaning that astrometric monitoring of just a few years would be adequate to generate constrained orbital fits and dynamical masses for the systems. In combination with their young ages, these binaries will prove to be excellent benchmarks for calibrating substellar evolutionary models down to a very low-mass regime.

  • 6. Currie, Thayne
    et al.
    Brandt, Timothy D.
    Uyama, Taichi
    Nielsen, Eric L.
    Blunt, Sarah
    Guyon, Olivier
    Tamura, Motohide
    Marois, Christian
    Mede, Kyle
    Kuzuhara, Masayuki
    Groff, Tyler D.
    Jovanovic, Nemanja
    Kasdin, N. Jeremy
    Lozi, Julien
    Hodapp, Klaus
    Chilcote, Jeffrey
    Carson, Joseph
    Martinache, Frantz
    Goebel, Sean
    Grady, Carol
    McElwain, Michael
    Akiyama, Eiji
    Asensio-Torres, Ruben
    Stockholm University, Faculty of Science, Department of Astronomy.
    Hayashi, Masa
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Knapp, Gillian R.
    Kwon, Jungmi
    Nishikawa, Jun
    Oh, Daehyeon
    Schlieder, Joshua
    Serabyn, Eugene
    Sitko, Michael
    Skaf, Nour
    SCExAO/CHARIS Near-infrared Direct Imaging, Spectroscopy, and Forward-Modeling of kappa And b: A Likely Young, Low-gravity Superjovian Companion2018In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 156, no 6, article id 291Article in journal (Refereed)
    Abstract [en]

    We present SCExAO/CHARIS high-contrast imaging/JHK integral field spectroscopy of kappa And b, a directly imaged low-mass companion orbiting a nearby B9V star. We detect kappa And b at a high signal-to-noise ratio and extract high-precision spectrophotometry using a new forward-modeling algorithm for (A-)LOCI complementary to KLIP-FM developed by Pueyo et al. kappa And b's spectrum best resembles that of a low-gravity LO-L1 dwarf (L0-L1 gamma). Its spectrum and luminosity are very well matched by 2MASS J0141-4633 and several other 12.5-15 M-J free-floating members of the 40 Myr old Tuc-Hor Association, consistent with a system age derived from recent interferometric results for the primary, a companion mass at/near the deuterium-burning limit (13(-2)(+12) M-J), and a companion-to-primary mass ratio characteristic of other directly imaged planets (q similar to 0.0051(-0.001)(+0.005)). We did not unambiguously identify additional, more closely orbiting companions brighter and more massive than kappa And b down to p similar to 0.'' 3 (15 au). SCExAO/CHARIS and complementary Keck/NIRC2 astrometric points reveal clockwise orbital motion. Modeling points toward a likely eccentric orbit: a subset of acceptable orbits include those that are aligned with the star's rotation axis. However, kappa And b's semimajor axis is plausibly larger than 55 au and in a region where disk instability could form massive companions. Deeper high-contrast imaging of kappa And and low-resolution spectroscopy from extreme adaptive optics systems such as SCExAO/CHARIS and higher-resolution spectroscopy from Keck/OSIRIS or, later, IRIS on the Thirty Meter Telescope could help to clarify kappa And b's chemistry and whether its spectrum provides an insight into its formation environment.

  • 7. Currie, Thayne
    et al.
    Marois, Christian
    Cieza, Lucas
    Mulders, Gijs D.
    Lawson, Kellen
    Caceres, Claudio
    Rodriguez-Ruiz, Dary
    Wisniewski, John
    Guyon, Olivier
    Brandt, Timothy D.
    Kasdin, N. Jeremy
    Groff, Tyler D.
    Lozi, Julien
    Chilcote, Jeffrey
    Hodapp, Klaus
    Jovanovic, Nemanja
    Martinache, Frantz
    Skaf, Nour
    Lyra, Wladimir
    Tamura, Motohide
    Asensio-Torres, Ruben
    Stockholm University, Faculty of Science, Department of Astronomy.
    Dong, Ruobing
    Grady, Carol
    Gerard, Benjamin
    Fukagawa, Misato
    Hand, Derek
    Hayashi, Masahiko
    Henning, Thomas
    Kudo, Tomoyuki
    Kuzuhara, Masayuki
    Kwon, Jungmi
    McElwain, Michael W.
    Uyama, Taichi
    No Clear, Direct Evidence for Multiple Protoplanets Orbiting LkCa 15: LkCa 15 bcd are Likely Inner Disk Signals2019In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 877, no 1, article id L3Article in journal (Refereed)
    Abstract [en]

    Two studies utilizing sparse aperture-masking (SAM) interferometry and H-alpha differential imaging have reported multiple Jovian companions around the young solar-mass star, LkCa 15 (LkCa 15 bcd): the first claimed direct detection of infant, newly formed planets (protoplanets). We present new near-infrared direct imaging/spectroscopy from the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system coupled with Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) integral field spectrograph and multi-epoch thermal infrared imaging from Keck/NIRC2 of LkCa 15 at high Strehl ratios. These data provide the first direct imaging look at the same wavelengths and in the same locations where previous studies identified the LkCa 15 protoplanets, and thus offer the first decisive test of their existence. The data do not reveal these planets. Instead, we resolve extended emission tracing a dust disk with a brightness and location comparable to that claimed for LkCa 15 bcd. Forward-models attributing this signal to orbiting planets are inconsistent with the combined SCExAO/CHARIS and Keck/NIRC2 data. An inner disk provides a more compelling explanation for the SAM detections and perhaps also the claimed H-alpha detection of LkCa 15 b. We conclude that there is currently no clear, direct evidence for multiple protoplanets orbiting LkCa 15, although the system likely contains at least one unseen Jovian companion. To identify Jovian companions around LkCa 15 from future observations, the inner disk should be detected and its effect modeled, removed, and shown to be distinguishable from planets. Protoplanet candidates identified from similar systems should likewise be clearly distinguished from disk emission through modeling.

  • 8. Hodosan, G.
    et al.
    Helling, Ch.
    Asensio-Torres, Ruben
    Stockholm University, Faculty of Science, Department of Astronomy. Universidad de La Laguna, Spain.
    Vorgul, I.
    Rimmer, P. B.
    Lightning climatology of exoplanets and brown dwarfs guided by Solar system data2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 461, no 4, p. 3927-3947Article in journal (Refereed)
    Abstract [en]

    Clouds form on extrasolar planets and brown dwarfs where lightning could occur. Lightning is a tracer of atmospheric convection, cloud formation and ionization processes as known from the Solar system, and may be significant for the formation of prebiotic molecules. We study lightning climatology for the different atmospheric environments of Earth, Venus, Jupiter and Saturn. We present lightning distribution maps for Earth, Jupiter and Saturn, and flash densities for these planets and Venus, based on optical and/or radio measurements from the World Wide Lightning Location Network and Sferics Timing and Ranging Network radio networks, the Lightning Imaging Sensor/Optical Transient Detector satellite instruments, the Galileo, Cassini, New Horizons and Venus Express spacecraft. We also present flash densities calculated for several phases of two volcano eruptions, Eyjafjallajokull's (2010) and Mt Redoubt's (2009). We estimate lightning rates for sample, transiting and directly imaged extrasolar planets and brown dwarfs. Based on the large variety of exoplanets, six categories are suggested for which we use the lightning occurrence information from the Solar system. We examine lightning energy distributions for Earth, Jupiter and Saturn. We discuss how strong stellar activity may support lightning activity. We provide a lower limit of the total number of flashes that might occur on transiting planets during their full transit as input for future studies. We find that volcanically very active planets might show the largest lightning flash densities. When applying flash densities of the large Saturnian storm from 2010/11, we find that the exoplanet HD 189733b would produce high lightning occurrence even during its short transit.

  • 9.
    Janson, Markus
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Asensio-Torres, Ruben
    Stockholm University, Faculty of Science, Department of Astronomy.
    André, Damien
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bonnefoy, Mickaël
    Delorme, Philippe
    Reffert, Sabine
    Desidera, Silvano
    Langlois, Maud
    Chauvin, Gaël
    Gratton, Raffaele
    Bohn, Alexander J.
    Eriksson, Simon C.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Marleau, Gabriel-Dominique
    Mamajek, Eric E.
    Vigan, Arthur
    Carson, Joseph C.
    The B-Star Exoplanet Abundance Study: a co-moving 16-25 M-Jup companion to the young binary system HIP 790982019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 626, article id A99Article in journal (Refereed)
    Abstract [en]

    Wide low-mass substellar companions are known to be very rare among low-mass stars, but appear to become increasingly common with increasing stellar mass. However, B-type stars, which are the most massive stars within similar to 150 pc of the Sun, have not yet been examined to the same extent as AFGKM-type stars in that regard. In order to address this issue, we launched the ongoing B-star Exoplanet Abundance Study (BEAST) to examine the frequency and properties of planets, brown dwarfs, and disks around B-type stars in the Scorpius-Centaurus (Sco-Cen) association; we also analyzed archival data of B-type stars in Sco-Cen. During this process, we identified a candidate substellar companion to the B9-type spectroscopic binary HIP 79098 AB, which we refer to as HIP 79098 (AB)b. The candidate had been previously reported in the literature, but was classified as a background contaminant on the basis of its peculiar colors. Here we demonstrate that the colors of HIP 79098 (AB)b are consistent with several recently discovered young and low-mass brown dwarfs, including other companions to stars in Sco-Cen. Furthermore, we show unambiguous common proper motion over a 15-yr baseline, robustly identifying HIP 79098 (AB)b as a bona fide substellar circumbinary companion at a 345 +/- 6 AU projected separation to the B9-type stellar pair. With a model-dependent mass of 16-25 M-Jup yielding a mass ratio of <1%, HIP 79098 (AB)b joins a growing number of substellar companions with planet-like mass ratios around massive stars. Our observations underline the importance of common proper motion analysis in the identification of physical companionship, and imply that additional companions could potentially remain hidden in the archives of purely photometric surveys.

  • 10.
    Janson, Markus
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Thalmann, Christian
    Boccaletti, Anthony
    Maire, Anne-Lise
    Zurlo, Alice
    Marzari, Francesco
    Meyer, Michael R.
    Carson, Joseph C.
    Augereau, Jean-Charles
    Garufi, Antonio
    Henning, Thomas
    Desidera, Silvano
    Asensio-Torres, Ruben
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pohl, Adriana
    DETECTION OF SHARP SYMMETRIC FEATURES IN THE CIRCUMBINARY DISK AROUND AK Sco2016In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 816, no 1, article id L1Article in journal (Refereed)
    Abstract [en]

    The Search for Planets Orbiting Two Stars survey aims to study the formation and distribution of planets in binary systems by detecting and characterizing circumbinary planets and their formation environments through direct imaging. With the SPHERE Extreme Adaptive Optics instrument, a good contrast can be achieved even at small (< 300 mas) separations from bright stars, which enables studies of planets and disks in a separation range that was previously inaccessible. Here, we report the discovery of resolved scattered light emission from the circumbinary disk around the well-studied young double star AK. Sco, at projected separations in the similar to 13-40 AU range. The sharp morphology of the imaged feature is surprising, given the smooth appearance of the disk in its spectral energy distribution. We show that the observed morphology can be represented either as a highly eccentric ring around AK Sco, or as two separate spiral arms in the disk, wound in opposite directions. The relative merits of these interpretations are discussed, as well as whether these features may have been caused by one or several circumbinary planets interacting with the disk.

  • 11. Olofsson, J.
    et al.
    van Holstein, R. G.
    Boccaletti, A.
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy. Max Planck Institut für Astronomie, Germany.
    Thebault, P.
    Gratton, R.
    Lazzoni, C.
    Kral, Q.
    Bayo, A.
    Canovas, H.
    Caceres, C.
    Ginski, C.
    Pinte, C.
    Asensio-Torres, Ruben
    Stockholm University, Faculty of Science, Department of Astronomy.
    Chauvin, G.
    Desidera, S.
    Henning, Th
    Langlois, M.
    Milli, J.
    Schlieder, J. E.
    Schreiber, M. R.
    Augereau, J-C
    Bonnefoy, M.
    Buenzli, E.
    Brandner, W.
    Durkan, Stephen
    Stockholm University, Faculty of Science, Department of Astronomy. Queen’s University Belfast, Northern Ireland, UK .
    Engler, N.
    Feldt, M.
    Godoy, N.
    Grady, C.
    Hagelberg, J.
    Lagrange, A-M
    Lannier, J.
    Ligi, R.
    Maire, A-L
    Mawet, D.
    Menard, F.
    Mesa, D.
    Mouillet, D.
    Peretti, S.
    Perrot, C.
    Salter, G.
    Schmidt, T.
    Sissa, E.
    Thalmann, C.
    Vigan, A.
    Abe, L.
    Feautrier, P.
    Le Mignant, D.
    Moulin, T.
    Pavlov, A.
    Rabou, P.
    Rousset, G.
    Roux, A.
    Resolving faint structures in the debris disk around TWA 7 Tentative detections of an outer belt, a spiral arm, and a dusty cloud2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 617, article id A109Article in journal (Refereed)
    Abstract [en]

    Context. Debris disks are the intrinsic by-products of the star and planet formation processes. Most likely due to instrumental limitations and their natural faintness, little is known about debris disks around low mass stars, especially when it comes to spatially resolved observations. Aims. We present new VLT/SPHERE IRDIS dual-polarization imaging (DPI) observations in which we detect the dust ring around the M2 spectral type star TWA 7. Combined with additional angular differential imaging observations we aim at a fine characterization of the debris disk and setting constraints on the presence of low-mass planets. Methods. We modeled the SPHERE DPI observations and constrain the location of the small dust grains, as well as the spectral energy distribution of the debris disk, using the results inferred from the observations, and performed simple N-body simulations. Results. We find that the dust density distribution peaks at similar to 0.72 '' (25 au), with a very shallow outer power-law slope, and that the disk has an inclination of similar to 13 degrees with a position angle of similar to 91 degrees east of north. We also report low signal-to-noise ratio detections of an outer belt at a distance of similar to 1.5 '' (similar to 52 au) from the star, of a spiral arm in the southern side of the star, and of a possible dusty clump at 0.11 ''. These findings seem to persist over timescales of at least a year. Using the intensity images, we do not detect any planets in the close vicinity of the star, but the sensitivity reaches Jovian planet mass upper limits. We find that the SED is best reproduced with an inner disk at similar to 0.2 '' (similar to 7 au) and another belt at 0.72 '' (25 au). Conclusions. We report the detections of several unexpected features in the disk around TWA 7. A yet undetected 100 M-circle plus planet with a semi-major axis at 20-30 au could possibly explain the outer belt as well as the spiral arm. We conclude that stellar winds are unlikely to be responsible for the spiral arm.

  • 12. Uyama, Taichi
    et al.
    Currie, Thayne
    Hori, Yasunori
    De Rosa, Robert J.
    Mede, Kyle
    Brandt, Timothy D.
    Kwon, Jungmi
    Guyon, Olivier
    Lozi, Julien
    Jovanovic, Nemanja
    Martinache, Frantz
    Kudo, Tomoyuki
    Tamura, Motohide
    Kasdin, N. Jeremy
    Groff, Tyler
    Chilcote, Jeffrey
    Hayashi, Masahiko
    McElwain, Michael W.
    Asensio-Torres, Ruben
    Stockholm University, Faculty of Science, Department of Astronomy.
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Knapp, Gillian R.
    Serabyn, Eugene
    Atmospheric Characterization and Further Orbital Modeling of kappa Andromeda b2020In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 159, no 2, article id 40Article in journal (Refereed)
    Abstract [en]

    We present kappa Andromeda b's photometry and astrometry taken with Subaru/SCExAO+HiCIAO and Keck/NIRC2, combined with recently published SCExAO/CHARIS low-resolution spectroscopy and published thermal infrared photometry to further constrain the companion's atmospheric properties and orbit. The Y/Y-K colors of kappa And b are redder than field dwarfs, consistent with its youth and lower gravity. Empirical comparisons of its Y-band photometry and CHARIS spectrum to a large spectral library of isolated field dwarfs reaffirm the conclusion from Currie et al. that it likely has a low gravity but admit a wider range of most plausible spectral types (L0-L2). Our gravitational classification also suggests that the best-fit objects for kappa And b may have lower gravity than those previously reported. Atmospheric models lacking dust/clouds fail to reproduce its entire 1-4.7 mu m spectral energy distribution (SED), and cloudy atmosphere models with temperatures of similar to 1700-2000 K better match kappa And b data. Most well-fitting model comparisons favor 1700-1900 K, a surface gravity of log(g) similar to 4-4.5, and a radius of 1.3-1.6 R-Jup; the best-fit model (Drift-Phoenix) yields the coolest and lowest-gravity values: T-eff = 1700 K and log g = 4.0. An update to kappa And b's orbit with ExoSOFT using new astrometry spanning 7 yr reaffirms its high eccentricity (0.77 0.08). We consider a scenario where unseen companions are responsible for scattering kappa And b to a wide separation and high eccentricity. If three planets, including kappa And b, were born with coplanar orbits, and one of them was ejected by gravitational scattering, a potential inner companion with mass greater than or similar to 10 M-Jup could be located at less than or similar to 25 au.

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