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Finding Ultracool Brown Dwarfs with UKIDSS SDSS IRTF/SpeX

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Finding Ultracool Brown Dwarfs with UKIDSS SDSS IRTF/SpeX. Kuenley Chiu, Andy Bunker (Exeter/AAO) Michael ... Finding optical dropouts with SDSS UKIDSS ... – PowerPoint PPT presentation

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Title: Finding Ultracool Brown Dwarfs with UKIDSS SDSS IRTF/SpeX


1
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

2
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 lt 1300 K, Lbol lt 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.

3
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
4
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 z7 quasar
J
J
known T8
i z Y J H
5
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.
6
SpeX prism mode offers excellent sensitivity and
gets 0.8-2.5 ?m in one shot. We classified T
dwarfs as faint as J18.8 (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
7
SpeX prism mode offers excellent sensitivity and
gets 0.8-2.5 ?m in one shot. We classified T
dwarfs as faint as J18.8 (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
8
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.
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