Investigation of faint galactic carbon stars from the First Byurakan Spectral Sky Survey. IV. GAIA DR2 data

Abstract

The second Gaia data release (Gaia DR2) data are used to analyze and estimate some important parameters for 127 carbon (C) type stars (56 are late N - type Asymptotic Giant Branch (AGB) C stars, 71 are early type CH giants) detected on the First Byurakan Spectral Sky Survey (FBS) low-resolution (lr) spectral plates. Gaia DR2 G broad band magnitudes are in the range 9.4m < G < 18.2m. for FBS C stars. Radial velocities (RV) is available for 75 C stars out of 127. For 9 objects RV is greater than 200 km/s. Absolute magnitudes in V band are estimated for 18 FBS C stars, having luminosity data, from which 17 are CH giants. They are in the range between -3.5m ≤ MV < +0.5m. For FBS 1918+869 absolute magnitude MV = -3.4(±0.2)m, which is typical for N type AGB C stars. Having distance estimations, the Hertzsprung-Russell diagram (HRD, or color - absolute magnitude diagram) was constructed for C stars. All FBS detected C stars are giants and AGB stars in the Galactic Halo. They are not far than 14 kpc from the Sun and 8 kpc from the Galactic plane.