A search for faint galactic carbon stars from the First Byurakan Spectral Sky Survey. I.

We present and analyse in this paper the first results of a systematic sear ch for Galactic carbon (C) stars using the First Byurakan Spectral Sky Surv ey (FBS). The present surveyed area extends over similar to 6140 deg(2) on the sky corresponding to similar to1/3 of the complete FBS Survey. Accurate positions, spectral classifications, approximate B and R magnitudes, and f inding charts are provided for 35 objects. Identification and spectral subc lasses (R or N) of those stars, belonging to the magnitude range 10.5 less than or equal toR less than or equal to 16.4, were determined by scrutinizi ng the Byurakan Schmidt telescope objective-prism plates. Subsequent slit-s pectroscopic observations were obtained by us for 21 stars, confirming the carbon nature of them all. From this result, it is assumed that the remaini ng C star candidates are most likely carbon-rich stars as well. 18 of the l isted objects at a Galactic latitude (\b \ >30 degrees) are faint enough (R >11.0) to be considered as Faint High Latitude Carbon (FHLC) stars accordin g to the definition of Totten & Irwin (1998). JHK magnitudes for 23 objects of our list are provided by the 2MASS database. Approximate distances are estimated from R and/or JHK data. Most of the stars are located between d s imilar or equal to7 and d similar or equal to 25 kpc from the Sun while the ir distances z to the Galactic plane range from about 2 to 25 kpc. The most distant object of our sample is found at d similar or equal to 45 kpc and z similar or equal to 40 kpc. It is interesting to note that the rate of ne wly discovered FBS FHLC star- one object per 200 deg(2)-is comparable to th at achieved by other previous surveys. Consequently it is reasonable to exp ect that the full exploitation of the FBS plates might result in the identi fication of about 45 new FHLC stars.