Optical spectroscopy of Be stars: peak separation of Balmer emission lines

The Be stars display variable optical emission lines originating in the circumstellar disc. Here we analyse high resolution spectroscopic observations of Be stars and the distance between the peaks of H-alpha, H-beta, and H-gamma emission lines ($\mathrm{\Delta }{V}_{\alpha }$, $\mathrm{\Delta }{V}_{\beta }$, and $\mathrm{\Delta }{V}_{\gamma }$ respectively). Combining published data, spectra from the ELODIE archive (obtained in the period 1998 – 2003) and Rozhen spectra (obtained 2015 – 2023) of 93 Be stars, we find a set of relations connecting $\mathrm{\Delta }{V}_{\alpha }$, $\mathrm{\Delta }{V}_{\beta }$ and $\mathrm{\Delta }{V}_{\gamma }$. They are effective for $30\le \mathrm{\Delta }{V}_{\alpha }\le 500$ km s${}^{-1}$, $80\le \mathrm{\Delta }{V}_{\beta }\le 600$ km s${}^{-1}$, and $40\le \mathrm{\Delta }{V}_{\gamma }\le 300$ km s${}^{-1}$. The new equations are in the form $y=ax+b$ and are valid for a wider velocity range than in previous studies.