Study of Faint Galactic Carbon Stars from the First Byurakan Spectral Sky Survey. IV. GAIA DR2 Data

Abstract

Data from the second Gaia release (Gaia DR2) are used to analyze and evaluate several important parameters for 127 carbon (C) stars of which 56 are AGB stars of class N and 71 are giants of early CH classes detected in low-dispersion spectral plates from the First Byurakan Survey (FBS). For the FBS C-stars Gaia DR2 G broad – band magnitudes are in the range 9m.4 < G < 18m.2. The radial velocities RV are accessible for 75 of the 127 C-stars. For 9 of them RV exceeds 200 km/s. For 18 of the FBS C-stars that have luminosity data in DR2, of which 17 are CH giants, the absolute V magnitudes are estimated to lie in the range -3m .4 ≤ MV ≤+0m.5. For FBS 1918+869 the absolute magnitude MV= – 3m.4 ± 0m.2, which is typical for N type AGB C-stars. A Hertzsprung-Russell diagram (HRD or color-absolute magnitude diagram) was constructed with the estimated distances for the 127 C-stars. All the observed FBS 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.