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In this study, researchers utilized the UKIRT Infrared Deep Sky Survey (UKIDSS) along with the Sloan Digital Sky Survey (SDSS) and IRTF/SpeX to uncover ultracool T dwarfs. These T dwarfs are the coldest, faintest objects beyond the Solar System that can be directly imaged. Through optical dropout techniques, the team identified faint red point sources and confirmed four new T dwarfs, including the coolest one, T7.5. The research aims to expand the understanding of these low-mass objects and determine their space densities for deeper insights into stellar physics and gas giant planets outside our solar system.
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Finding Ultracool Brown Dwarfs with UKIDSS + SDSS + IRTF/SpeX • Kuenley Chiu, Andy Bunker (Exeter/AAO) • Michael Liu, Katelyn Allers, Trent Dupuy (IfA/Hawaii) • Linhua Jiang, Xiaohui Fan (Arizona) • Dan Stark (Caltech), Karl Glazebrook (Swinburne) • MNRAS, in press
Why hunt for T dwarfs (and why with IRTF/SpeX)? • T dwarfs are the coldest, faintest objects outside the Solar System that can be directly imaged. • Teff < 1300 K, Lbol < 10-5 Lsun • Probes of “stellar” physics in the ultracool regime. • Key pathway for studying extrasolar gas giant planets. • Most of emergent flux is in the near-IR, and thus key diagnostics of their properties (T, g, Z) are at these wavelenths. • IRTF/SpeX is especially well suited for these studies.
SDSS The newly operational UKIRT Infrared Deep Sky Survey (UKIDSS) has been generating approx. 250 square degrees of YJHK imaging data per semester, overlapping the SDSS, and provides the first significant new dataset to explore T dwarfs since 2MASS. Using optical dropout techniques, we have been selecting and following up faint red point source candidates, seeking late T dwarfs (and Y dwarfs) and high-redshift quasars. 0.8 sq deg tiled footprint
Finding optical dropouts with SDSS + UKIDSS J H K High-z quasars and T dwarfs display similar strong color decrements between the optical (i & z) and the near-IR (Y & J). Based on spectra of template objects, color selections are carried out on the matched SDSS optical and UKIDSS near-IR catalogs to identify candidate objects. model z=7 quasar J J known T8 i z Y J H
Optical and near-IR confirmation imaging identifies genuine promising objects, and photometry + colors discriminate between BDs and quasars. Optical spectroscopy is used to identify high-z QSOs (Ly- around 9000A), and IRTF/Spex near-IR spectroscopy used to classify brown dwarfs.
SpeX prism mode offers excellent sensitivity and gets 0.8-2.5 m in one shot. We classified T dwarfs as faint as J=18.8 (Vega), probably the faintest IR spectra ever published from a 3-4m class telescope. Four new T dwarfs found, the coolest one being T7.5 (three plotted here). Chiu et al 2008, MNRAS
SpeX prism mode offers excellent sensitivity and gets 0.8-2.5 m in one shot. We classified T dwarfs as faint as J=18.8 (Vega), probably the faintest IR spectra ever published from a 3-4m class telescope. Four new T dwarfs found, the coolest one being T7.5 (three plotted here). Chiu et al 2008, MNRAS
Chiu et al 2008, MNRAS The 4 T dwarfs found are among the faintest yet known, and found via optical dropout, complementary to IR-only selection. The sample continues to grow, ~2 dozen T dwarfs now known from UKIDSS data, providing rich followup observations. Goal is to get the space densities of these very low mass objects.
