Do Miras show the long secondary periods?

TL;DR

This study investigates whether Mira variable stars can exhibit long secondary periods, analyzing a large sample from the Large Magellanic Cloud to identify potential candidates and explore the physical or observational reasons behind LSP phenomena.

Contribution

The paper provides the first systematic search for long secondary periods in Miras, identifying potential candidates and discussing their characteristics and implications.

Findings

7% of Miras in the sample show potential LSP signatures

Most LSP candidates are C-rich stars

Long secondary periods in Miras may exist but require further confirmation

Abstract

The long secondary period (LSP) phenomenon, which is commonly observed in pulsating red giants, has not been detected in any Mira yet. The goal of this paper is to verify, if there is a physical reason for this or if it is simply an observational bias. The OGLE-III Sample of Long Period Variables in the Large Magellanic Cloud, containing 1663 Miras, is used to perform a search for secondary periodicity in these objects and identify candidates for the long secondary period stars based on the location on the period-luminosity diagram. Out of 1663 Miras, 108 were identified as potential candidates, with variability broadly consistent with LSP. This makes 7% of the whole Mira sample in the Large Magellanic Cloud. Most, if not all of the Mira LSP candidates are C-rich stars. The results of this analysis suggest that Miras may exhibit long secondary periods. However, the long-term variability can also be related to period and amplitude irregularities that Miras are known to exhibit. Further study will be necessary to draw a definitive conclusion.