Bibcode
Burningham, Ben; Pinfield, D. J.; Lucas, P. W.; Leggett, S. K.; Deacon, N. R.; Tamura, M.; Tinney, C. G.; Lodieu, N.; Zhang, Z. H.; Huelamo, N.; Jones, H. R. A.; Murray, D. N.; Mortlock, D. J.; Patel, M.; Barrado Y Navascués, D.; Zapatero Osorio, M. R.; Ishii, M.; Kuzuhara, M.; Smart, R. L.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 406, Issue 3, pp. 1885-1906.
Advertised on:
8
2010
Citations
125
Refereed citations
101
Description
We report the discovery of 47 new T dwarfs in the Fourth Data Release
(DR4) from the Large Area Survey (LAS) of the United Kingdom Infrared
Telescope (UKIRT) Infrared Deep Sky Survey with spectral types ranging
from T0 to T8.5. These bring the total sample of LAS T dwarfs to 80 as
of DR4. In assigning spectral types to our objects we have identified
eight new spectrally peculiar objects, and divide seven of them into two
classes. H2O-H-early have a H2O-H index that
differs with the H2O-J index by at least two subtypes.
CH4-J-early have a CH4-J index that disagrees with
the H20-J index by at least two subtypes. We have ruled out
binarity as a sole explanation for both types of peculiarity, and
suggest that they may represent hitherto unrecognized tracers of
composition and/or gravity. Clear trends in z'(AB) - J and Y - J are
apparent for our sample, consistent with weakening absorption in the red
wing of the KI line at 0.77μm with decreasing effective temperature.
We have used our sample to estimate space densities for T6-T9 dwarfs. By
comparing our sample to Monte Carlo simulations of field T dwarfs for
various mass functions of the form ψ(M)
~M-αpc-3M-1solar, we
have placed weak constraints on the form of the field mass function. Our
analysis suggests that the substellar mass function is declining at
lower masses, with negative values of α preferred. This is at odds
with results for young clusters that have been generally found to have
α > 0.