| Issue |
A&A
Volume 506, Number 2, November I 2009
|
|
|---|---|---|
| Page(s) | L25 - L28 | |
| Section | Letters | |
| DOI | https://doi.org/10.1051/0004-6361/200912954 | |
| Published online | 15 September 2009 | |
Letter to the Editor
A new extremely low-mass white dwarf in the NLTT catalogue*
Astronomický ústav, Akademie věd České republiky, Fričova 298, 251 65 Ondřejov, Czech Republic e-mail: [kawka;vennes]@sunstel.asu.cas.cz
Received:
22
July
2009
Accepted:
14
September
2009
We report on the discovery of the extremely low-mass, hydrogen-rich white dwarf, NLTT 11748. Based on measurements of the effective temperature (8540 ± 50 K) and surface gravity (log g = 6.20 ± 0.15) obtained by fitting the observed Balmer line profiles with synthetic spectra, we derive a mass of 0.167 ± 0.005 
. This object is one of only a
handful of white dwarfs with masses below 0.2 that are believed to be the product of close binary evolution with an episode of Roche lobe overflow onto a degenerate companion (neutron star or white dwarf). Assuming membership in the halo population, as suggested by the kinematics and adopting a cooling age of 
Gyr for the white dwarf, we infer a progenitor mass of 0.87-0.93 . The likely companion has yet to be identified, but a search for radial velocity variations may help constrain its nature.
Key words: white dwarfs / stars: individual: NLTT 11748 / stars: atmospheres
© ESO, 2009
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