Intriguing triple-mode RR Lyrae star with period doubling

TL;DR

This paper reports the discovery of a triple-mode RR Lyrae star exhibiting period doubling, with unusual period ratios that challenge existing pulsation models, suggesting possible non-radial modes.

Contribution

The study identifies a rare triple-mode RR Lyrae star with period doubling, highlighting discrepancies with current pulsation models and proposing alternative interpretations.

Findings

Discovery of a triple-mode RR Lyrae star with period doubling

Period ratios do not match existing pulsation models

Possible non-radial mode excitation suggested

Abstract

We report the discovery of an intriguing triple-mode RR Lyrae star found in the OGLE Galactic bulge collection, OGLE-BLG-RRLYR-24137. In the OGLE catalog the star was identified as RRd star - double-mode pulsator, pulsating simultaneously in the fundamental and in the first overtone modes. We find that third mode is excited and firmly detect its period doubling. Period ratios are not far from that expected for triple-mode - fundamental, first and third overtone - pulsation. Unfortunately, we cannot reproduce period ratios of the three modes with a consistent set of pulsation models. Therefore the other interpretation, that additional mode is non-radial, is also likely.