The Solar-Type Contact Binary BX Pegasi Revisited

TL;DR

This study provides new photometric observations of the contact binary BX Peg, revealing magnetic activity, brightness disturbances, and complex period variations including potential additional companions or magnetic cycles.

Contribution

It offers the first detailed analysis of short-term brightness disturbances and models magnetic activity effects with updated period change insights for BX Peg.

Findings

Brightness disturbances linked to magnetic activity modeled with star spots.

Complex period variations include secular decrease and possible third or fourth companions.

Short-term oscillations suggest additional bodies or magnetic cycles.

Abstract

We present the results of new CCD photometry for the contact binary BX Peg, made during three successive months beginning on September 2008. As do historical light curves, our observations display an O'Connell effect and the November data by themselves indicate clear evidence for very short-time brightness disturbance. For these variations, model spots are applied separately to the two data set of Group I (Sep.--Oct.) and Group II (Nov.). The former is described by a single cool spot on the secondary photosphere and the latter by a two-spot model with a cool spot on the cool star and a hot one on either star. These are generalized manifestations of the magnetic activity of the binary system. Twenty light-curve timings calculated from Wilson-Devinney code were used for a period study, together with all other minimum epochs. The complex period changes of BX Peg can be sorted into a secular period decrease caused dominantly by angular momentum loss due to magnetic stellar wind braking, a light-travel-time (LTT) effect due to the orbit of a low-mass third companion, and a previously unknown short-term oscillation. This last period modulation could be produced either by a second LTT orbit with a period of about 16 yr due to the existence of a fourth body or by the effect of magnetic activity with a cycle length of about 12 yr.