The H$α$ line emission of the Be star $β$ Psc: the last 40 years

Abstract

A study on the photosphere and disc of the Be star $β$ Psc is presented. We recover almost 40 years of high-resolution spectroscopic observations and additional data gathered from the BeSS database. We evaluate the photospheric parameters from the SED and fittings of state-of-the-art non-LTE model atmospheres to observed helium, carbon, silicon and magnesium line profiles. Our models include the stellar geometric deformation as well as the co-latitude dependence of temperature and gravity, aiming to derive the effects of rotation on the stellar parameters. We estimate the circumstellar disc parameters from the fitting of models assuming different disc properties, namely its radius and gas density profile. The disc inclination angle $i$ is constrained from the fittings of He I 4471 Å, Mg II 4481 Å, C II 4267 Å, and Si II 4128, 4132 Å lines with gravity darkened models. Our findings, based on model fittings, suggest that during the last 40 years the disc radius changed within the interval $5.5 \le R_d \le 7.8$ $R_*$, the disc base gas density within $5 \times 10^{-13} \le ρ\le 1 \times 10^{-12} g cm^{-3}$, while the radial power-law density index $m$ assumed values between 2.0 and 2.3. These results are in agreement with recent works dealing with spectroscopic and interferometric measurements of this object.