Pulsation and orbit of AU Pegasi

TL;DR

This study investigates AU Pegasi, a binary pulsating star, revealing it pulsates in two modes simultaneously with a stable period of 2.411 days, challenging its previous classification as a Type II Cepheid.

Contribution

It provides the first detailed analysis of AU Pegasi's pulsation modes and their stability, suggesting a reclassification of the star based on its pulsation characteristics.

Findings

AU Pegasi pulsates in two modes with a frequency ratio of 0.706.

The pulsation period stabilized at 2.411 days after rapid increase.

Evidence suggests AU Pegasi may not be a Type II Cepheid.

Abstract

AU Pegasi is a pulsating star in a spectroscopic binary system with an orbital period of 53.26 days. Between 1960 and 1990 an extremely rapid period increase was observed in the value of the pulsation period, but in the last 15 years the observation show that the period set in 2.411 days. Fourier analysis of photometric data obtained during the ASAS project and those taken at the Piszkesteto Mountain Station of the Konkoly Observatory during 1994-2005 indicate that AU Pegasi is pulsating in two modes simultaneously, and the ratio of the frequencies of the two modes is 0.706, a value common for double-mode classical Cepheids. A careful analysis of other photometric observations obtained during the era of the strong period increase also revealed existence of a second mode. This may suggest that this star is not a Type II Cepheid, despite its galactic position.