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

Abstract

We present and analyse in this paper the first results of a systematic search for Galactic carbon (C) stars using the First Byurakan Spectral Sky Survey (FBS). The present surveyed area extends over ~6140 deg2 on the sky corresponding to ~ of the complete FBS Survey. Accurate positions, spectral classifications, approximate B and R magnitudes, and finding charts are provided for 35 objects. Identification and spectral subclasses (R or N) of those stars, belonging to the magnitude range 10.5 ≤ R ≤ 16.4, were determined by scrutinizing the Byurakan Schmidt telescope objective-prism plates. Subsequent slit-spectroscopic observations were obtained by us for 21 stars, confirming the carbon nature of them all. From this result, it is assumed that the remaining C star candidates are most likely carbon-rich stars as well. 18 of the listed objects at a Galactic latitude (°) are faint enough () to be considered as Faint High Latitude Carbon (FHLC) stars according to the definition of Totten & Irwin ([CITE]). 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 7 and 25 kpc from the Sun while their distances z to the Galactic plane range from about 2 to 25 kpc. The most distant object of our sample is found at 45 kpc and kpc. It is interesting to note that the rate of newly discovered FBS FHLC stars -one object per 200 deg2 -is comparable to that achieved by other previous surveys. Consequently it is reasonable to expect that the full exploitation of the FBS plates might result in the identification of about 45 new FHLC stars.