X-ray properties of RR Lyrae and Cepheid variables from eROSITA

TL;DR

This study searches for X-ray emissions from RR Lyrae and Cepheid variables using eROSITA data, identifying a potential first X-ray detection of an RR Lyrae star and exploring correlations between X-ray luminosity and pulsation period.

Contribution

It reports the first plausible X-ray detection of an RR Lyrae star and analyzes X-ray luminosity trends in Cepheids, providing new insights into pulsating star high-energy emissions.

Findings

Potential first X-ray detection of an RR Lyrae star.

X-ray luminosity increases with pulsation period in Cepheids.

Type II Cepheids show higher X-ray luminosity at similar periods.

Abstract

We present a search for X-ray counterparts to RR Lyrae and Cepheid variables using data from the first eROSITA all-sky survey. We identify seven RR Lyrae and eight Cepheid variables with positional matches to X-ray sources. While most Cepheid associations appear reliable, the RR Lyrae matches are predominantly spurious. Only one source, OGLE-BLG-RRLYR-00252, appears to be a plausible RR Lyrae detection, potentially representing the first observational evidence of X-ray emission from a star of this type. Its inferred luminosity suggests that RR Lyrae stars are intrinsically at least two orders of magnitude fainter in X-rays than the brightest Cepheids. We also observe a tentative increase in X-ray luminosity with pulsation period among classical Cepheids, and higher luminosities in type II Cepheids at comparable periods. These trends may reflect intrinsic differences in atmospheric structure and shock efficiency, offering new insight into the mechanisms driving high-energy emission in pulsating stars.