Far-ultraviolet investigation into the galactic globular cluster M30 (NGC 7099): II. Potential X-ray counterparts and variable sources

TL;DR

This study uses far-ultraviolet observations from HST to identify potential X-ray counterparts and variable sources in the globular cluster M30, revealing new and known variable stars and their associations.

Contribution

It provides the first FUV-based identification of X-ray counterparts and variable sources in M30, including new variable classifications and correlations with known X-ray sources.

Findings

Six confident matches between FUV objects and X-ray sources.

Identification of new variable sources including a dwarf nova and weak variables.

Confirmation of known RR Lyrae variables through FUV variability analysis.

Abstract

We present a far-ultraviolet (FUV) study of the globular cluster M30 (NGC 7099). The images were obtained using the Advanced Camera for Surveys (ACS/SBC, F150LP, FUV) and the Wide Field Planetary Camera 2 (WFPC2, F300W, UV) on board the Hubble Space Telescope (HST). We compare the catalogue of FUV objects to ten known X-ray sources and find six confident matches of two cataclysmic variables (CVs), one RS CVn, one red giant with strong FUV emission and two sources only detected in the FUV. We also searched for variable sources in our dataset and found a total of seven blue stragglers (BSs), four horizontal branch (HB) stars, five red giant branch stars, 28 main sequence stars and four gap objects that demonstrated variability. One BS star is a known W-UMa contact binary, one of the gap objects is a known CV identified in this work to be a dwarf nova, and the three other gap sources are weak variables. The periods and positions of two of the variable HB stars match them to two previously known RR Lyrae variables of types RRab and RRc.