Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey

Abstract

We present the discovery of fifteen new T2.5-T7.5 dwarfs (with estimated distances between ~24-93pc, identified in the first three main data releases of the UKIRT Infrared Deep Sky Survey. This brings the total number of T dwarfs discovered in the Large Area Survey (to date) to 28. These discoveries are confirmed by near infrared spectroscopy, from which we derive spectral types on the unified scheme of Burgasser et al. (2006). Seven of the new T dwarfs have spectral types of T2.5-T4.5, five have spectral types of T5-T5.5, one is a T6.5p, and two are T7-7.5. We assess spectral morphology and colours to identify T dwarfs in our sample that may have non-typical physical properties (by comparison to solar neighbourhood populations). The colours of the full sample of LAS T dwarfs show a possible trend to bluer Y-J with decreasing effective temperature beyond T8. By accounting for the main sources of incompleteness (selection, follow-up and spatial) as well as the effects of unresolved binarity and Malmquist bias, we estimate that there are 17+-4 >=T4 dwarfs in the J<=19 volume of the LAS second data release. Comparing this to theoretical predictions is most consistent with a sub-stellar mass function exponent alpha between -1.0 and 0. This is consistent with the latest 2MASS/SDSS constraint (which is based on lower number statistics), and is significantly lower than the alpha~1.0 suggested by L dwarf field populations, possibly a result of the lower mass range probed by the T dwarf class.

21 pages, 7 figures, submitted to MNRAS

References in corpus (25)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The WFCAM Science Archive
• Meeting the Cool Neighbors. IX. The Luminosity Function of M7-L8 Ultracool Dwarfs in the Field
• Discovery of Two T Dwarf Companions with the Spitzer Space Telescope
• The UKIRT Infrared Deep Sky Survey Early Data Release
• Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition
• Ammonia as a tracer of chemical equilibrium in the T7.5 dwarf Gliese 570D
• Discovery of 11 New T Dwarfs in the Two Micron All-Sky Survey, Including a Possible L/T Transition Binary
• JHK Observations of Faint Standard Stars in the Mauna Kea Near-Infrared Photometric System
• A search for binary systems among the nearest L dwarfs
• A very cool brown dwarf in UKIDSS DR1
• A Cross-Match of 2MASS and SDSS: Newly-Found L and T Dwarfs and an Estimate of the Space Densitfy of T Dwarfs
• Physical parameters of two very cool T dwarfs
• Physical and Spectral Characteristics of the T8 and Later-Type Dwarfs
• Finding benchmark brown dwarfs to probe the IMF as a function of time
• HD3651B: the first directly imaged brown dwarf companion of an exoplanet host star
• The Physical Properties of HD 3651B: An Extrasolar Nemesis?
• Proper motion L and T dwarf candidate members of the Pleiades
• Discovery of a nearby L-T transition object in the Southern Galactic plane
• New constraints on the membership of the T dwarf S Ori 70 in the sigma Orionis cluster
• Two T dwarfs from the UKIDSS Early Data Release
• Broad-band photometric colors and effective temperature calibrations for late-type giants. II. Z<0.02
• The possiblity of detection of Ultracool Dwarfs with the UKIRT Infrared Deep Sky Survey
• Four Faint T Dwarfs from the UKIRT Infrared Deep Sky Survey (UKIDSS) Southern Stripe
• Southern Infrared Proper Motion Survey III: Constraining the mass function of low mass stars

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• The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs
• A Volume-Limited Sample of Ultracool Dwarfs. I. Construction, Space Density, and a Gap in the L/T Transition
• A large spectroscopic sample of L and T dwarfs from UKIDSS LAS: peculiar objects, binaries, and space density
• The Hawaii Infrared Parallax Program. IV. A Comprehensive Parallax Survey of L0-T8 dwarfs with UKIRT
• An Infrared High Proper Motion Survey Using 2MASS and SDSS: Discovery of M, L and T Dwarfs
• Self-consistent Models of Y Dwarf Atmospheres with Water Clouds and Disequilibrium Chemistry
• Ultra-cool dwarfs: new discoveries, proper motions, and improved spectral typing from SDSS and 2MASS photometric colors
• Primeval very low-mass stars and brown dwarfs - VI. Population properties of metal-poor degenerate brown dwarfs
• The Dawes Review 3: The Atmospheres of Extrasolar Planets and Brown Dwarfs
• The Hawaii Infrared Parallax Program. V. New T-Dwarf Members and Candidate Members of Nearby Young Moving Groups
• The UKIDSS-2MASS Proper Motion Survey I: Ultracool dwarfs from UKIDSS DR4
• Discovery of a new Y dwarf: WISE J030449.03-270508.3
• NGTS-19b : A high mass transiting brown dwarf in a 17-day eccentric orbit
• An eccentric Brown Dwarf eclipsing an M dwarf
• Exploring the planetary-mass population in the Upper Scorpius association
• Characterization of the known T type dwarfs towards the Sigma Orionis cluster
• 49 new T dwarfs identified using methane imaging
• Two distant brown dwarfs in the UKIRT Infrared Deep Sky Survey Deep Extragalactic Survey Data Release 2
• Discovery of a resolved white dwarf-brown dwarf binary with a small projected separation: SDSS J222551.65+001637.7AB
• The Small Magellanic Cloud through the lens of the James Webb Space Telescope : binaries and mass function within the galaxy outskirts
• A deep HST view of the open cluster NGC2158: binaries, mass functions, and M-dwarf discontinuity
• Binary frequency of planet-host stars at wide separations: A new brown dwarf companion to a planet-host star
• Using Old and New Approaches: Determining Physical Properties of Brown Dwarfs with Empirical Relations and Machine Learning Models