AU Pegasi revisited: period evolution and orbital elements of a peculiar Type II Cepheid

TL;DR

This study revisits AU Pegasi, revealing its period has been mostly constant with an overall increase, and uncovers a new periodic behavior likely linked to tidal effects from its binary companion, along with revised orbital parameters.

Contribution

It provides new insights into AU Pegasi's period evolution and orbital elements, challenging previous assumptions and identifying a previously unknown periodicity.

Findings

Period mostly constant with overall increase

Discovery of a new periodic behavior in the $O-C$ diagram

Revised orbital elements of the binary system

Abstract

New analysis on the period changes of Type II Cepheid AU Peg is presented. The available recent photometric measurements were collected and analysed with various methods. The period has been found to be constant for certain time intervals, although increasing in overall, in contrast with the previous expectations, which suggested the period change to reverse. Superimposed on overall period change, a formerly unknown periodic behaviour has been found in the $O-C$ diagram of AU Peg, which cannot be matched to the radial velocity variations. Since the Cepheid is a member of a binary system, it is probable that the unusual period change is in connection with the companion's tidal force. The orbital elements of the binary system involving AU Peg have been also revised.