Abstract
Although photometric and spectroscopic observations of Be stars (γ Cas-type variable stars) have been carried out for many years, there are many things that remain unclear, such as the mechanism of angular momentum transport to the circumstellar disk (in the case of binary systems, is there also a contribution from the companion star). Spectroscopic monitoring observations of several Be stars were performed using the Small Aperture Telescope + low-dispersion spectrograph at the school observatory starting in September 2018. As a result, we hypothesized that “the disk is ringed by tidal forces when the Be star’s companion passes through the perihelion point” (石田2022, Stars and Galaxies, 5, 10). To test this hypothesis, we performed medium-dispersion spectroscopic observations of Be stars δ Sco and π Aqr using the Nayuta Telescope at the Nishi-Harima Observatory, University of Hyogo, during and after the periastron passage of their respective companion stars. Combined with the results of the BeSS database analysis, no ring formation of the disk was observed. Combined with the observations at the School Observatory, the disk at δ Sco is expected to be expanding due to a decrease in effective temperature, and may be headed for extinction in the future. In the disk of π Aqr, the effective temperature of the disk tends to change around the perihelion. From these results, it is possible that the companion star has a significant effect on the angular momentum transport mechanism of the Be star to the disk.
