BV Photometry and Hα Spectroscopy of the Rs-Canum Binary II-Pegasi

Abstract

Differential BV photometry of II Peg obtained on a total of 57 nights during the years 1986-1991 and Hα spectroscopy obtained on 12 nights during the 1990-1991 observing season are presented. From an analysis of the available data on this object we find that significant changes in the mean light level of the system occur from season to season. The maximum light level had maintained a value less than or equal to 7.35 mag during 1976-1983, but after a drop in 1985 it has shown a slight increase from 1986 onwards. At larger amplitudes the brightness at minimum is found to decrease and the brightness at maximum to increase. During the period 1974-1991 we could identifiy a total of six spots or spot groups from te migration of the ? and their life times range from two to seven years. The light curve obtained during 1989-1990 season was modelled assuming that the light variation is caused by a single circular spot. The resulting spot parameters reproduce the V and B light curves reasonably well; however, a substantial fraction of the spot lies in the invisible hemisphere indicating that the approximation of the spot or spot group by an equivalent circular spot is not valid. The Hα equivalent widths show a strengthening near the minimum of the light curve. The spectra obtained on one night (22 Nov 1990) show evidence of an optical flare.