The brightest pure-H ultracool white dwarf
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Author
Catalan, S.
Tremblay, P. -E.
Pinfield, D.J.
Smith, Leigh
Zhang, Z. H.
Napiwotzki, R.
Marocco, F.
Day-Jones, A. C.
Gomes, J.
Forde, K.P.
Lucas, P.W.
Jones, H.R.A.
Attention
2299/13936
Abstract
We report the identification of LSR J0745+2627 in the United Kingdom InfraRed Telescope Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) as a cool white dwarf with kinematics and age compatible with the thick-disk/halo population. LSR J0745+2627 has a high proper motion (890 mas/yr) and a high reduced proper motion value in the J band (H-J = 21.87). We show how the infrared-reduced proper motion diagram is useful for selecting a sample of cool white dwarfs with low contamination. LSR J0745+2627 is also detected in the Sloan Digital Sky Survey (SDSS) and the Wide-field Infrared Survey Explorer (WISE). We have spectroscopically confirmed this object as a cool white dwarf using X-Shooter on the Very Large Telescope. A detailed analysis of its spectral energy distribution reveals that its atmosphere is compatible with a pure-H composition model with an effective temperature of 3880 +/- 90 K. This object is the brightest pure-H ultracool white dwarf (T-eff <4000 K) ever identified. We have constrained the distance (24-45 pc), space velocities and age considering different surface gravities. The results obtained suggest that LSR J0745+2627 belongs to the thick-disk/halo population and is also one of the closest ultracool white dwarfs.