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Register a new userA search for photometric variability in the young T3.5 planetary-mass companion GU Psc b
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Marie-Eve Naud
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We present a photometric $J$-band variability study of GU Psc b, a T3.5 co-moving planetary-mass companion (9-13$M_{rm{Jup}}$) to a young ($sim$150 Myr) M3 member of the AB Doradus Moving Group. The large separation between GU Psc b and its host star (42) provides a rare opportunity to study the photometric variability of a planetary-mass companion. The study presented here is based on observations obtained from 2013 to 2014 over three nights with durations of 5-6 hr each with the WIRCam imager at Canada-France-Hawaii Telescope. Photometric variability with a peak-to-peak amplitude of $4pm1$% at a timescale of $sim$6 hr was marginally detected on 2014 October 11. No high-significance variability was detected on 2013 December 22 and 2014 October 10. The amplitude and timescale of the variability seen here, as well as its evolving nature, is comparable to what was observed for a variety of field T dwarfs and suggests that mechanisms invoked to explain brown dwarf variability may be applicable to low-gravity objects such as GU Psc b. Rotation-induced photometric variability due to the formation and dissipation of atmospheric features such as clouds is a plausible hypothesis for the tentative variation detected here. Additional photometric measurements, particularly on longer timescales, will be required to confirm and characterize the variability of GU Psc b, determine its periodicity and to potentially measure its rotation period.
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We present the discovery of a co-moving planetary-mass companion ~42 (~2000 AU) from a young M3 star, GU Psc, likely member of the young AB Doradus Moving Group (ABDMG). The companion was first identified via its distinctively red i - z color (> 3.5) through a survey made with Gemini-S/GMOS. Follow-up Canada-France-Hawaii Telescope/WIRCam near-infrared (NIR) imaging, Gemini-N/GNIRS NIR spectroscopy and Wide-field Infrared Survey Explorer photometry indicate a spectral type of T3.5+-1 and reveal signs of low gravity which we attribute to youth. Keck/Adaptive Optics NIR observations did not resolve the companion as a binary. A comparison with atmosphere models indicates Teff = 1000-1100 K and logg = 4.5-5.0. Based on evolution models, this temperature corresponds to a mass of 9-13 MJup for the age of ABDMG (70-130 Myr). The relatively well-constrained age of this companion and its very large angular separation to its host star will allow its thorough characterization and will make it a valuable comparison for planetary-mass companions that will be uncovered by forthcoming planet-finder instruments such as Gemini Planet Imager and SPHERE.
Among the greatest challenges in understanding ultra-cool brown dwarf and exoplanet atmospheres is the evolution of cloud structure as a function of temperature and gravity. In this study, we present the rotational modulations of GU Psc b -- a rare mid-T spectral type planetary-mass companion at the end of the L/T spectral type transition. Based on the HST/WFC3 1.1-1.67$rm, mu m$ time-series spectra, we observe a quasi-sinusoidal light curve with a peak-to-trough flux variation of 2.7 % and a minimum period of eight hours. The rotation-modulated spectral variations are weakly wavelength-dependent, or largely gray between 1.1-1.67$rm,mu$m. The gray modulations indicate that heterogeneous clouds are present in the photosphere of this low-gravity mid-T dwarf. We place the color and brightness variations of GU Psc b in the context of rotational modulations reported for mid-L to late-T dwarfs. Based on these observations, we report a tentative trend: mid-to-late T dwarfs become slightly redder in $J-H$ color with increasing $J$-band brightness, while L dwarfs become slightly bluer with increasing brightness. If this trend is verified with more T-dwarf samples, it suggests that in addition to the mostly gray modulations, there is a second-order spectral-type dependence on the nature of rotational modulations.
We present the identification of two previously known young objects in the solar neighbourhood as a likely very wide binary. TYC 9486-927-1, an active, rapidly rotating early-M dwarf, and 2MASS J21265040-8140293, a low-gravity L3 dwarf previously identified as candidate members of the $sim$45 Myr old Tucana Horologium association (TucHor). An updated proper motion measurement of the L3 secondary, and a detailed analysis of the pairs kinematics in the context of known nearby, young stars, reveals that they share common proper motion and are likely bound. New observations and analyses reveal the primary exhibits Li 6708~AA~absorption consistent with M dwarfs younger than TucHor but older than the $sim$10 Myr TW Hydra association yielding an age range of 10-45 Myr. A revised kinematic analysis suggests the space motions and positions of the pair are closer to, but not entirely in agreement with, the $sim$24 Myr old $beta$ Pictoris moving group. This revised 10-45 Myr age range yields a mass range of 11.6--15 M$_J$ for the secondary. It is thus likely 2MASS J21265040-8140293short is the widest orbit planetary mass object known ($>$4500AU) and its estimated mass, age, spectral type, and $T_{eff}$ are similar to the well-studied planet $beta$ Pictoris b. Because of their extreme separation and youth, this low-mass pair provide an interesting case study for very wide binary formation and evolution.
Aims: Our objective is the optical and near-infrared spectroscopic characterisation of 2MASS J0249-0557 c, a recently discovered young planetary mass companion to the $beta$ Pictoris member 2MASS J0249-0557. Methods: Using the Visible and Infrared Survey Telescope for Astronomy (VISTA) Hemisphere Survey (VHS) and the Two Micron All Sky Survey (2MASS) data, we independently identified the companion 2MASS J0249-0557 c. We obtained low-resolution optical spectroscopy of this object using the Optical System for Imaging and low-intermediate-Resolution Integrated Spectroscopy (OSIRIS) spectrograph at the Gran Telescopio Canarias (GTC), and near-infrared spectroscopy using the Son of Isaac (SofI) spectrograph on the New Technology Telescope (NTT). Results: We classified 2MASS J0249-0557 c with a spectral type of L2.5$pm$0.5 in the optical and L3$pm$1 in the near-infrared. We identified spectroscopic indicators of youth that are compatible with the age of the $beta$ Pictoris moving group. We also detect a strong H$alpha$ emission, with a pEW of -90$^{+20}_{-40}$A, which seems persistent in time. This indicates strong chromospheric activity or disk accretion. Although many M-type brown dwarfs have strong H$alpha$ emission, this target is one of the very few L-type planetary mass objects in which this strong H$alpha$ emission has been detected. Lithium absorption at 6708 A is observed with pEW $lesssim$ 5A. We also computed the binding energy of 2MASS J0249-0557 c and obtained an (absolute) upper limit of $U=(-8.8pm4.4) 10^{32}$ J. Conclusions: Similarly to other young brown dwarfs and isolated planetary mass objects, strong H$alpha$ emission is also present in young planetary mass companions at ages of some dozen million years. We also found that 2MASS J0249-0557 c is one of the wide substellar companions with the lowest binding energy known to date.
The Young Suns Exoplanet Survey (YSES) consists of a homogeneous sample of 70 young, solar-mass stars located in the Lower Centaurus-Crux subgroup of the Scorpius-Centaurus association with an average age of $15pm3,$Myr. We report the detection of a co-moving companion around the K3IV star TYC 8998-760-1 (2MASSJ13251211-6456207) that is located at a distance of $94.6pm0.3,$pc using SPHERE/IRDIS on the VLT. Spectroscopic observations with VLT/X-SHOOTER constrain the mass of the star to $1.00pm0.02,M_{odot}$ and an age of $16.7pm1.4,$Myr. The companion TYC 8998-760-1 b is detected at a projected separation of 1.71, which implies a projected physical separation of $162,$au. Photometric measurements ranging from $Y$ to $M$ band provide a mass estimate of $14pm3,M_mathrm{jup}$ by comparison to BT-Settl and AMES-dusty isochrones, corresponding to a mass ratio of $q=0.013pm0.003$ with respect to the primary. We rule out additional companions to TYC 8998-760-1 that are more massive than $12,M_mathrm{jup}$ and farther than $12,$au away from the host. Future polarimetric and spectroscopic observations of this system with ground and space based observatories will facilitate testing of formation and evolution scenarios shaping the architecture of the circumstellar environment around this young Sun.
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