Planets Around Low-Mass Stars (PALMS). V. Age-Dating Low-Mass Companions to Members and Interlopers of Young Moving Groups

Abstract

We present optical and near-infrared adaptive optics (AO) imaging and spectroscopy of 13 ultracool (>M6) companions to late-type stars (K7-M4.5), most of which have recently been identified as candidate members of nearby young moving groups (YMGs; 8-120 Myr) in the literature. The inferred masses of the companions (~10-100 Mjup) are highly sensitive to the ages of the primary stars so we critically examine the kinematic and spectroscopic properties of each system to distinguish bona fide YMG members from old field interlopers. 2MASS J02155892-0929121 C is a new M7 substellar companion (40-60 Mjup) with clear spectroscopic signs of low gravity and hence youth. The primary, possibly a member of the ~40 Myr Tuc-Hor moving group, is visually resolved into three components, making it a young low-mass quadruple system in a compact (<100 AU) configuration. In addition, Li 1 $\lambda$6708 absorption in the intermediate-gravity M7.5 companion 2MASS J15594729+4403595 B provides unambiguous evidence that it is young (<200 Myr) and resides below the hydrogen burning limit. Three new close-separation (<1") companions (2MASS J06475229-2523304 B, PYC J11519+0731 B, and GJ 4378 Ab) orbit stars previously reported as candidate YMG members, but instead are likely old (>1 Gyr) tidally-locked spectroscopic binaries without convincing kinematic associations with any known moving group. The high rate of false positives in the form of old active stars with YMG-like kinematics underscores the importance of radial velocity and parallax measurements to validate candidate young stars identified via proper motion and activity selection alone. Finally, we spectroscopically confirm the cool temperature and substellar nature of HD 23514 B, a recently discovered M8 benchmark brown dwarf orbiting the dustiest-known member of the Pleiades. [Abridged]

Accepted to ApJ

References in corpus (34)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Constraining the Age-Activity Relation for Cool Stars: The SDSS DR5 Low-Mass Star Spectroscopic Sample
• Tertiary companions to close spectroscopic binaries
• Stellar SEDs from 0.3-2.5 Microns: Tracing the Stellar Locus and Searching for Color Outliers in SDSS and 2MASS
• On the age of the $\beta$ Pictoris moving group
• Low-Mass Dwarf Template Spectra from the Sloan Digital Sky Survey
• The Automated Palomar 60-Inch Telescope
• A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf "Lithium Test" at Early Ages
• Characterizing Young Brown Dwarfs using Low Resolution Near-IR Spectra
• Planets Around Low-Mass Stars (PALMS). IV. The Outer Architecture of M Dwarf Planetary Systems
• M dwarfs: effective temperatures, radii and metallicities
• A Stellar Census of the Tucana-Horologium Moving Group
• PPM-Extended (PPMX) - a catalogue of positions and proper motions
• JHK Observations of Faint Standard Stars in the Mauna Kea Near-Infrared Photometric System
• Lithium Depletion of Nearby Young Stellar Associations
• TASS Mark IV Photometric Survey of the Northern Sky
• A VLBI Resolution of the Pleiades Distance Controversy
• Discovery of a wide planetary-mass companion to the young M3 star GU Psc
• Keck Laser Guide Star Adaptive Optics Monitoring of 2MASS J1534-2952AB: First Dynamical Mass Determination of a Binary T Dwarf
• High-efficiency Autonomous Laser Adaptive Optics
• Meeting the Cool Neighbors X: Ultracool dwarfs from the 2MASS All-Sky Data Release
• Warm dust in the terrestrial planet zone of a sun-like Pleiad: collisions between planetary embryos?
• Prospecting in Ultracool Dwarfs: Measuring the Metallicities of Mid- and Late-M Dwarfs
• Wide, Cool and Ultracool Companions to Nearby Stars from Pan-STARRS1
• Discovery of an M9.5 Candidate Brown Dwarf in the TW Hydrae Association - DENIS J124514.1-442907
• New Evidence for a Substellar Luminosity Problem: Dynamical Mass for the Brown Dwarf Binary Gl 417BC
• Discovery of 9 New Companions to Nearby Young M Stars with the Altair AO System
• The Trigonometric Parallax of the Brown Dwarf Planetary System 2MASSW J1207334-393254
• The LuckyCam Survey for Very Low Mass Binaries II: 13 new M4.5-M6.0 Binaries
• The Detection of Low Mass Companions in Hyades Cluster Spectroscopic Binary Stars
• GG Tau: the fifth element
• Orbital Monitoring of the AstraLux Large M-dwarf Multiplicity Sample
• Rotational periods and evolutionary models for subgiant stars observed by CoRoT
• Astrometric Calibration of the Gemini NICI Planet-Finding Campaign

Cited by in corpus (16)

• Hints for a Turnover at the Snow Line in the Giant Planet Occurrence Rate
• Population-Level Eccentricity Distributions of Imaged Exoplanets and Brown Dwarf Companions: Dynamical Evidence for Distinct Formation Channels
• A path towards understanding the rotation-activity relation of M dwarfs with K2 mission, X-ray and UV data
• All-sky Co-moving Recovery Of Nearby Young Members. (ACRONYM) II: The Beta Pictoris Moving Group
• Obliquity Constraints on an Extrasolar Planetary-Mass Companion
• Rotation Periods, Inclinations, and Obliquities of Cool Stars Hosting Directly Imaged Substellar Companions: Spin-Orbit Misalignments are Common
• ACRONYM III: Radial Velocities for 336 Candidate Young Low-Mass Stars in the Solar Neighborhood, Including 78 Newly Confirmed Young Moving Group Members
• The GAPS Programme with HARPS-N at TNG. XXXVII. A precise density measurement of the young ultra-short period planet TOI-1807 b
• The Elusive Majority of Young Moving Groups. I. Young Binaries and Lithium-Rich Stars in the Solar Neighborhood
• The Orbital Eccentricities of Directly Imaged Companions Using Observable-Based Priors: Implications for Population-level Distributions
• The McDonald Accelerating Stars Survey (MASS): White Dwarf Companions Accelerating the Sun-like Stars 12 Psc and HD 159062
• Joint Radial Velocity and Direct Imaging Planet Yield Calculations: I. Self-consistent Planet Populations
• The Influence of 10 Unique Chemical Elements in Shaping the Distribution of Kepler Planets
• Large Adaptive Optics Survey for Substellar Objects (LASSO) Around Young, Nearby, Low-mass Stars with Robo-AO
• Dynamical Mass of the Young Brown Dwarf Companion PZ Tel B
• Characterising Young Visual M-dwarf Binaries with Near-Infrared Integral Field Spectra