Letter to the Editor

Discovery of a peculiar DQ white dwarf ^*,**

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

Corresponding author: D. Carollo, carollo@to.astro.it

Received: 23 January 2002
Accepted: 2 August 2002

Abstract

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 ( arcsec/yr) and faint apparent magnitude () suggest a nearby object of low luminosity. A low-resolution spectrum taken with the William Herschel Telescope clearly shows strong C₂ 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_eff. Comparison of our spectrophotometric data to published synthetic spectra suggests 6000 K 8000 K, although further analysis with specialized synthetic models appear necessary to derive both T_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.