Study of the Balmer decrements for Galactic classical Be stars using the Himalayan Chandra Telescope of India

Abstract

In a recent study, Banerjee et al. (2021) produced an atlas of all major emission lines found in a large sample of 115 Galactic field Be stars using the 2-m Himalayan Chandra Telescope (HCT) facility located at Ladakh, India. This paper presents our further exploration of these stars to estimate the electron density in their discs. Our study using Balmer decrement values indicate that their discs are generally optically thick in nature with electron density (n_e) in their circumstellar envelopes (CEs) being in excess of 10^13 cm^-3 for around 65% of the stars. For another 19% stars, the average n_e in their discs probably range between 10^12 cm^-3 and 10^13 cm^-3. We noticed that the nature of the H{\alpha} and H\b{eta} line profiles might not influence the observed Balmer decrement values (i.e. D_34 and D_54) of the sample of stars. Interestingly, we also found that around 50% of the Be stars displaying D_34 greater than 2.7 are of earlier spectral types, i.e. within B0 -B3.