Very Low-Mass Stars and Brown Dwarfs in Upper Scorpius using Gaia DR1: Mass Function, Disks and Kinematics

Abstract

Our understanding of the brown dwarf population in star forming regions is dependent on knowing distances and proper motions, and therefore will be improved through the Gaia space mission. In this paper, we select new samples of very low mass objects (VLMOs) in Upper Scorpius using UKIDSS colors and optimised proper motions calculated using Gaia DR1. The scatter in proper motions from VLMOs in Upper Scorpius is now (for the first time) dominated by the kinematic spread of the region itself, not by the positional uncertainties. With age and mass estimates updated using Gaia parallaxes for early type stars in the same region, we determine masses for all VLMOs. Our final most complete sample includes 453 VLMOs of which $\sim$125 are expected to be brown dwarfs. The cleanest sample is comprised of 131 VLMOs, with $\sim$105 brown dwarfs. We also compile a joint sample from the literature which includes 415 VLMOs, out of which 152 are likely brown dwarfs. The disc fraction among low-mass brown dwarfs ($M<0.05M_{\odot }$) is substantially higher than in more massive objects, indicating that discs around low-mass brown dwarfs survive longer than in low-mass stars overall. The mass function for $0.01<M<0.1$ $M_{\odot }$ is consistent with the Kroupa IMF. We investigate the possibility that some 'proper motion outliers' have undergone a dynamical ejection early in their evolution. Our analysis shows that the color-magnitude cuts used when selecting samples introduce strong bias into the population statistics due to varying level of contamination and completeness.

arXiv comment18 pages, 10 figures, 10 tables, 9 pages of appendices. Accepted for publication in AJ

References in corpus (52)

• Astropy: A Community Python Package for Astronomy
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• On the variation of the Initial Mass Function
• The Gaia mission
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• The VizieR database of Astronomical Catalogues
• Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• A Hipparcos census of the nearby OB associations
• Evolutionary models for very-low-mass stars and brown dwarfs with dusty atmospheres
• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• The PPMXL catalog of positions and proper motions on the ICRS. Combining USNO-B1.0 and 2MASS
• The UKIRT Infrared Deep Sky Survey ZYJHK Photometric System: Passbands and Synthetic Colours
• Gaia Data Release 1: Astrometry - one billion positions, two million proper motions and parallaxes
• A Revised Age for Upper Scorpius and The Star-Formation History Among the F-Type Members of the Scorpius-Centaurus OB Association
• The WFCAM Science Archive
• A Steeper than Linear Disk Mass-Stellar Mass Scaling Relation
• The UKIRT Wide Field Camera ZYJHK Photometric System: Calibration from 2MASS
• The Star-formation History and Accretion-Disk Fraction Among the K-Type Members of the Scorpius-Centaurus OB Association
• Gaia Data Release 1: Catalogue validation
• The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation
• A temperate rocky super-Earth transiting a nearby cool star
• A rocky planet transiting a nearby low-mass star
• The Disk Population of the Upper Scorpius Association
• The Formation and Early Evolution of Low-mass Stars and Brown Dwarfs
• The UKIRT Infrared Deep Sky Survey Early Data Release
• Exploring brown dwarf disks: A 1.3 mm survey in Taurus
• New Low-Mass Members of the Taurus Star-Forming Region
• A Disk Census for Young Brown Dwarfs
• UCAC5: New Proper Motions using Gaia DR1
• Results of the ROTOR-program. II. The long-term photometric variability of weak-line T Tauri stars
• A Large-Area Search for Low-Mass Objects in Upper Scorpius II: Age and Mass Distributions
• Evolution of brown dwarf disks: A Spitzer survey in Upper Scorpius
• Hot Stuff for One Year (HSOY) - A 583 million star proper motion catalogue derived from Gaia DR1 and PPMXL
• Substellar Objects in Nearby Young Clusters (SONYC) VI: The planetary-mass domain of NGC1333
• Low Mass Stars and Substellar Objects in the NGC 1333 Molecular Cloud
• Gaia data release 1: Principles of the photometric calibration of the G band
• Multi-fibre optical spectroscopy of low-mass stars and brown dwarfs in Upper Sco
• Gaia data release 1, the photometric data
• Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey: IV Upper Sco
• Joint astrometric solution of Hipparcos and Gaia: A recipe for the Hundred Thousand Proper Motions project
• Hunting for planets in the HL Tau disk
• Near Infrared Spectroscopy of Young Brown Dwarfs in Upper Scorpius
• Age spreads and the temperature dependence of age estimates in Upper Sco
• Probing the Upper Scorpius mass function in the planetary-mass regime
• New brown dwarfs in the south part of the Upper Scorpius Association
• Brown Dwarf Disks at Ages of 5-10 Myr
• The dynamical evolution of low-mass hydrogen-burning stars, brown dwarfs and planetary-mass objects formed through disc fragmentation
• Gaia Data Release 1: Validation of the photometry
• A Method for Selecting M dwarfs with an Increased Likelihood of Unresolved Ultra-cool Companionship
• Low-resolution near-infrared spectroscopic signatures of unresolved ultracool companions to M dwarfs

Cited by in corpus (18)

• Refining the Census of the Upper Scorpius Association with Gaia
• A Census of the Stellar Populations in the Sco-Cen Complex
• New Young Stars and Brown Dwarfs in the Upper Scorpius Association
• X-shooter spectroscopy of young stars with disks. The TW Hydrae association as a probe of the final stages of disk accretion
• A Gaia Survey for Young Stars Associated with the Lupus Clouds
• Three-dimensional structure of the Upper Scorpius association with the Gaia first data release
• Isochronal age-mass discrepancy of young stars: SCExAO/CHARIS integral field spectroscopy of the HIP 79124 triple system
• HST survey of the Orion Nebula Cluster in the H${}_2$O 1.4 $\mu$m absorption band: I. A census of substellar and planetary mass objects
• A novel survey for young substellar objects with the W-band filter VI: Spectroscopic census of sub-stellar members and the IMF of $\sigma$ Orionis cluster
• Substructure, supernovae, and a time-resolved star formation history for Upper Scorpius
• What and Whence 1I/`Oumuamua: A Contact Binary from the Debris of a Young Planetary System?
• Exploring the planetary-mass population in the Upper Scorpius association
• Disks around young planetary-mass objects: Ultradeep Spitzer imaging of NGC1333
• The Rotation-Disk Connection in Young Brown Dwarfs: Strong Evidence for Early Rotational Braking
• Spectral characterization of young LT dwarfs
• Spectroscopy of Candidate Members of the Sco-Cen Complex
• The extended Gaia-PS1-SDSS (GPS1+) proper motion catalog
• DECam Survey for Low-Mass Stars and Substellar Objects in the UCL and LCC Subgroups of the Sco-Cen OB Association (SCOCENSUS)