EDP Sciences
Free access
Volume 393, Number 3, October III 2002
Page(s) L45 - L48
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20021130

A&A 393, L45-L48 (2002)
DOI: 10.1051/0004-6361:20021130


Discovery of a peculiar DQ white dwarf

D. Carollo1, S. T. Hodgkin2, A. Spagna1, R. L. Smart1, M. G. Lattanzi1, B. J. McLean3 and D. J. Pinfield4

1  INAF, Osservatorio Astronomico di Torino, 10025 Pino Torinese, Italy
2  Cambridge Astronomical Survey Unit, Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK
3  Space Telescope Science Institute (STScI), Baltimore, MD 21218, USA
4  Astrophysics Research Institute, Liverpool John Moores University, Birkenhead, CH41 1LD, UK

(Received 23 January 2002 / Accepted 2 August 2002)

We report the discovery of a new carbon rich white dwarf that was identified during a proper motion survey for cool white dwarfs based on photographic material used for the construction of the Guide Star Catalog II. Its large proper motion ( $\mu\simeq
0.48$ arcsec/yr) and faint apparent magnitude ( $V\simeq 18.7$) suggest a nearby object of low luminosity. A low-resolution spectrum taken with the William Herschel Telescope clearly shows strong C 2 Deslandres-d'Azambuja and Swan bands, which identify the star as a DQ white dwarf. The strength of the Deslandres-d'Azambuja bands and the depression of the continuum in the Swan-band region are signs of enhanced carbon abundance for the given $T_{\rm eff}$. Comparison of our spectrophotometric data to published synthetic spectra suggests 6000 K $ < T_{\rm
eff} <$ 8000 K, although further analysis with specialized synthetic models appear necessary to derive both $T_{\rm eff}$ and chemical composition. Finally, the range of spatial velocity estimated for this object makes it a likely member of the halo or thick disk population.

Key words: white dwarfs -- stars: carbon -- stars: kinematics -- stars: individual: GSC2U J131147.2+292348 -- astrometry -- techniques: spectroscopic

Offprint request: D. Carollo, carollo@to.astro.it

© ESO 2002