New carbon stars found in the Digitized First Byurakan Survey

Universite de Versailles Saint-Quentin, CNRS/INSU, LATMOS-IPSL, 11 Bd D Alembert, 78280 Guyancourt e-mail:alain.sarkissian@latmos.ipsl.frReceived September 15, 1996; accepted March 16, 1997ABSTRACTContext. Faint high-latitude carbon stars (FHLCs) are distant, luminous giants. For this reason, they are often used to study thedynamical and chemical properties of the Galactic Halo. However, more accurate investigation of photometric and spectroscopicsurveys has revealed an increasing number of such objects with luminosities of main sequence stars.Aims.We report the first results of a systematic search of FHLCs usi ng the Digitized First Byurakan Survey (DFBS) low-resolution(lr) spectral database.Methods.The DFBS lr spectral plates are analyzed with the help of standard image analysis softwares in order to select faint earlyand late-type carbon star candidates. We observed and analyzed new optical spectra for the observed objects. Photometry for the newand known objects was extracted from online databases.Results. More than 20 new faint high latitude carbon star candidates have been detected in a area of ∼4030 sq. deg. Moderateresolution slit spectroscopy was carried for all candidates. Carbon star nature was confirmed for thirteen of them. Five are N-typecarbon stars from which two are new discoveries while three are already confirmed by other researcher. DFBS J064958.54 +741610.1presented in FBS previous lists as a M8-M9 star appears now tobe a N-type star of late-subclasses. Eight objects show spectral energydistribution (SED) typical for early-type carbon stars. Nine carbon stars are new discoveries. The remaining objects are M-type stars(later than the M7 subclass). The estimated mass-loss rates, for the five N-type stars are in good agreement with the typical mass-loss rates found for such N-type carbon stars. Five stars, comparatively bright, are classified as a CH-type carbon stars based on thepresence of the strong G-band of the CH molecule absorbtion.Three new DFBS C stars could be dwarf Carbon (dC) star candidates.The heliocentric distances and absolute magnitudes were determined for the confirmed DFBS C stars.Conclusions.The results presented in this paper underline that the Digitized First Byurakan Survey low-resolution spectral databasecan be efficiently used to select and study early and late subclasses of the faint high-latitude carbon stars.Key words. stars: carbon –surveys – methods: observational – Galaxy: s tellar content