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Register a new userComprehensive analysis of HD 105, a young Solar System analog
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HD~105 is a nearby, pre-main sequence G0 star hosting a moderately bright debris disc ($L_{rm dust}/L_{star} sim 2.6times10^{-4}$). HD~105 and its surroundings might therefore be considered an analogue of the young Solar System. We refine the stellar parameters based on an improved Gaia parallax distance, identify it as a pre-main sequence star {with an age of 50~$pm$~16~Myr}. The circumstellar disc was marginally resolved by textit{Herschel}/PACS imaging at far-infrared wavelengths. Here we present an archival ALMA observation at 1.3~mm, revealing the extent and orientation of the disc. We also present textit{HST}/NICMOS and VLT/SPHERE near-infrared images, where we recover the disc in scattered light at the $geq$~5-$sigma$ level. This was achieved by employing a novel annular averaging technique, and is the first time this has been achieved for a disc in scattered light. Simultaneous modelling of the available photometry, disc architecture, and detection in scattered light allow better determination of the discs architecture, and dust grain minimum size, composition, and albedo. We measure the dust albedo to lie between 0.19 and 0.06, the lower value being consistent with Edgeworth-Kuiper belt objects.
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HD95086 (A8V, 17Myr) hosts a rare planetary system for which a multi-belt debris disk and a giant planet of 4-5MJup have been directly imaged. Our study aims to characterize the physical and orbital properties of HD95086b, search for additional planets at short and wide orbits and image the cold outer debris belt in scattered light. We used HARPS at the ESO 3.6m telescope to monitor the radial velocity of HD95086 over 2 years and investigate the existence of giant planets at less than 3au orbital distance. With the IRDIS dual-band imager and the IFS integral field spectrograph of SPHERE at VLT, we imaged the faint circumstellar environment beyond 10au at six epochs between 2015 and 2017. We do not detect additional giant planets around HD95086. We identified the nature (bound companion or background contaminant) of all point-like sources detected in the IRDIS field of view. None of them correspond to the ones recently discovered near the edge of the cold outer belt by ALMA. HD95086b is resolved for the first time in J-band with IFS. Its near-infrared spectral energy distribution is well fitted by a few dusty and/or young L7-L9 dwarf spectral templates. The extremely red 1-4um spectral distribution is typical of low-gravity objects at the L/T spectral type transition. The planets orbital motion is resolved between January 2015 and May 2017. Together with past NaCo measurements properly re-calibrated, our orbital fitting solutions favor a retrograde low to moderate-eccentricity orbit e=0.2 (0.0 to 0.5), with a semi-major axis 52au corresponding to orbital periods of 288$ yrs and an inclination that peaks at i = 141deg, which is compatible with a planet-disk coplanar configuration. Finally, we report the detection in polarimetric differential imaging of the cold outer debris belt between 100 and 300au, consistent in radial extent with recent ALMA 1.3mm resolved observations.
HD 95086 is a young early-type star that hosts (1) a 5 MJ planet at the projected distance of 56 AU revealed by direct imaging, and (2) a prominent debris disk. Here we report the detection of 69 um crystalline olivine feature from the disk using the Spitzer/MIPS-SED data covering 55-95 um. Due to the low resolution of MIPS-SED mode, this feature is not spectrally resolved, but is consistent with the emission from crystalline forsterite contributing 5% of the total dust mass. We also present detailed analysis of the disk SED and re-analysis of resolved images obtained by Herschel. Our results suggest that the debris structure around HD 95086 consists of a warm (175 K) belt, a cold (55 K) disk, and an extended disk halo (up to 800 AU), and is very similar to that of HR 8799. We compare the properties of the three debris components, and suggest that HD 95086 is a young analog of HR 8799. We further investigate and constrain single-planet, two-planet, three-planet and four-planet architectures that can account for the observed debris structure and are compatible with dynamical stability constraints. We find that equal-mass four-planet configurations of geometrically spaced orbits, with each planet of mass 5 MJ, could maintain the gap between the warm and cold debris belts, and also be just marginally stable for timescales comparable to the age of the system.
Abbreviated. By selecting stars with similar ages and masses, the Young Suns Exoplanet Survey (YSES) aims to detect and characterize planetary-mass companions to solar-type host stars in the Scorpius-Centaurus association. Our survey is carried out with VLT/SPHERE with short exposure sequences on the order of 5 min per star per filter. The subtraction of the stellar point spread function (PSF) is based on reference star differential imaging (RDI) using the other targets in the survey in combination with principal component analysis. We report the discovery of YSES 2b, a planetary-mass companion to the K1 star YSES 2 (TYC 8984-2245-1). The primary has a Gaia EDR3 distance of 110 pc, and we derive a revised mass of $1.1,M_odot$ and an age of approximately 14 Myr. We detect the companion in two observing epochs southwest of the star at a position angle of 205$^circ$ and with a separation of $sim1.05$, which translates to a minimum physical separation of 115 au at the distance of the system. We derive a photometric planet mass of $6.3^{+1.6}_{-0.9},M_mathrm{Jup}$ using AMES-COND and AMES-dusty evolutionary models; this mass corresponds to a mass ratio of $q=(0.5pm0.1)$% with the primary. This is the lowest mass ratio of a direct imaging planet around a solar-type star to date. We discuss potential formation mechanisms and find that the current position of the planet is compatible with formation by disk gravitational instability, but its mass is lower than expected from numerical simulations. Formation via core accretion must have occurred closer to the star, yet we do not find evidence that supports the required outward migration, such as via scattering off another undiscovered companion in the system. YSES 2b is an ideal target for follow-up observations to further the understanding of the physical and chemical formation mechanisms of wide-orbit Jovian planets.
Exoplanets orbiting pre-main sequence stars are laboratories for studying planet evolution processes, including atmospheric loss, orbital migration, and radiative cooling. V1298 Tau, a young solar analog with an age of 23 $pm$ 4 Myr, is one such laboratory. The star is already known to host a Jupiter-sized planet on a 24 day orbit. Here, we report the discovery of three additional planets --- all between the size of Neptune and Saturn --- based on our analysis of K2 Campaign 4 photometry. Planets c and d have sizes of 5.6 and 6.4 $R_oplus$, respectively and with orbital periods of 8.25 and 12.40 days reside 0.25% outside of the nominal 3:2 mean-motion resonance. Planet e is 8.7 $R_oplus$ in size but only transited once in the K2 time series and thus has a period longer than 36 days, but likely shorter than 223 days. The V1298 Tau system may be a precursor to the compact multiplanet systems found to be common by the Kepler mission. However, the large planet sizes stand in sharp contrast to the vast majority of Kepler multis which have planets smaller than 3 $R_oplus$. Simple dynamical arguments suggest total masses of $<$28 $M_oplus$ and $<$120 $M_oplus$ for the c-d and d-b planet pairs, respectively. The implied low masses suggest that the planets may still be radiatively cooling and contracting, and perhaps losing atmosphere. The V1298 Tau system offers rich prospects for further follow-up including atmospheric characterization by transmission or eclipse spectroscopy, dynamical characterization through transit-timing variations, and measurements of planet masses and obliquities by radial velocities.
Millimeter observations of disks around young stars reveal substructures indicative of gas pressure traps that may aid grain growth and planet formation. We present Submillimeter Array observations of HD 34700- two Herbig Ae stars in a close binary system (Aa/Ab, $sim$0.25 AU), surrounded by a disk presenting a large cavity and spiral arms seen in scattered light, and two distant, lower mass companions. These observations include 1.3 mm continuum emission and the $^{12}$CO 2-1 line at $sim0.5$ (178 AU) resolution. They resolve a prominent azimuthal asymmetry in the continuum, and Keplerian rotation of a circumbinary disk in the $^{12}$CO line. The asymmetry is located at a radius of $155^{+11}_{-7}$ AU, consistent with the edge of the scattered light cavity, being resolved in both radius ($72 ^{+14}_{-15}$ AU) and azimuth (FWHM = $64 ^{circ +8}_{-7}$). The strong asymmetry in millimeter continuum emission could be evidence for a dust trap, together with the more symmetric morphology of $^{12}$CO emission and small grains. We hypothesize an unseen circumbinary companion, responsible for the cavity in scattered light and creating a vortex at the cavity edge that manifests in dust trapping. The disk mass has limitations imposed by the detection of $^{12}$CO and non-detection of $^{13}$CO. We discuss its consequences for the potential past gravitational instability of this system, likely accounting for the rapid formation of a circumbinary companion. We also report the discovery of resolved continuum emission associated with HD 34700B (projected separation $sim1850$AU), which we explain through a circumstellar disk.
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