Multi-fibre optical spectroscopy of low-mass stars and brown dwarfs in Upper Sco

Abstract

We have obtained multi-fibre intermediate-resolution optical spectroscopy of 94 photometric and proper motion selected low-mass star and brown dwarf candidates in Upper Sco with AAT/AAOmega. We have estimated the spectral types and measured the equivalent widths of youth and gravity diagnostic features to confirm the spectroscopic membership of about 95% of the candidates extracted from 6.5 square degrees in Upper Sco. We also detect lithium in the spectra with the highest signal-to-noise, consolidating our conclusions about their youth. Furthermore, we derive an estimate of our selections using spectroscopic data obtained for a large number of stars falling into the instrument's field-of-view. We have estimated the effective temperatures and masses for each new spectroscopic member using the latest evolutionary models available for low-mass stars and brown dwarfs. Combining the current optical spectroscopy presented here with near-infrared spectroscopy obtained for the faintest photometric candidates, we confirm the shape and slope of our earlier photometric mass function. The luminosity function drawn from the spectroscopic sample of 113 USco members peaks at around M6 and is flat at later spectral type. We may detect the presence of the M7/M8 gap in the luminosity function as a result of the dust properties in substellar atmospheres. The mass function may peak at 0.2 Msun and is quite flat in the substellar regime. We observe a possible excess of cool low-mass brown dwarfs compared to IC 348 and the extrapolation of the field mass functions, supporting the original hypothesis that Upper Sco may possess an excess of brown dwarfs. This result shows that the selection of photometric candidates based on five band photometry available from the UKIDSS GCS and complemented partially by proper motions can lead to a good representation of the spectroscopic mass function (abridged).

Accepted by A&A: 18 pages with 9 figures and 3 tables in main, 2 figures and 4 tables in Appendices. Some tables in electronic format

References in corpus (13)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• Constraining the Age-Activity Relation for Cool Stars: The SDSS DR5 Low-Mass Star Spectroscopic Sample
• The Stellar Population of the Chamaeleon I Star-Forming Region
• Near-infrared cross-dispersed spectroscopy of brown dwarf candidates in the Upper Sco association
• A Large-Area Search for Low Mass Objects in Upper Scorpius I: The Photometric Campaign and New Brown Dwarfs
• A Large-Area Search for Low-Mass Objects in Upper Scorpius II: Age and Mass Distributions
• New brown dwarfs in Upper Sco using UKIDSS Galactic Cluster Survey science verification data
• Measuring tiny mass accretion rates onto young brown dwarfs
• Disks around Brown Dwarfs in the Sigma Orionis Cluster
• Multi-Object Spectroscopy Field Configuration by Simulated Annealing
• New members in the Upper Sco association from the UKIDSS Early Data Release
• Oph 1622-2405: Not a Planetary-Mass Binary
• On the properties of discs around accreting brown dwarfs

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• The optical+infrared L dwarf spectral sequence of young planetary-mass objects in the Upper Scorpius association
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• Near Infrared Spectroscopy of Young Brown Dwarfs in Upper Scorpius
• A new take on the low-mass brown dwarf companions on wide-orbits in Upper-Scorpius
• A Pulsation Search Among Young Brown Dwarfs and Very Low Mass Stars
• Probing the Upper Scorpius mass function in the planetary-mass regime
• An eclipsing double-line spectroscopic binary at the stellar/substellar boundary in the Upper Scorpius OB association
• New brown dwarfs in the south part of the Upper Scorpius Association
• A new free-floating planet in the Upper Scorpius association
• New members of the TW Hydrae Association and two accreting M-dwarfs in Scorpius-Centaurus
• Testing the fragmentation limit in the Upper Sco association
• Multiplicity of disc-bearing stars in Upper Scorpius and Upper Centaurus-Lupus
• Very Low-Mass Stars and Brown Dwarfs in Upper Scorpius using Gaia DR1: Mass Function, Disks and Kinematics
• Measuring the Initial Mass Function of Low Mass Stars and Brown Dwarfs
• Characterization of the known T type dwarfs towards the Sigma Orionis cluster
• USco1621 B and USco1556 B: Two wide companions at the deuterium-burning mass limit in Upper Scorpius
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• The Impact of Chromospheric Activity on Observed Initial Mass Functions
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• The CARMENES search for exoplanets around M dwarfs. Behaviour of the Paschen lines during flares and quiescence
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• Spectroscopy of Candidate Members of the Sco-Cen Complex
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