Far-ultraviolet investigation into the galactic globular cluster M30 (NGC 7099): I. Photometry and radial distributions

TL;DR

This study uses Hubble Space Telescope ultraviolet imaging to analyze the stellar populations and distributions in the globular cluster M30, revealing details about its main sequence, horizontal branch, blue stragglers, and potential cataclysmic variables.

Contribution

First detailed far-ultraviolet photometric analysis of M30, identifying various stellar populations and their radial distributions within the cluster.

Findings

Identified 1218 main sequence stars and 185 red giant branch stars.

Discovered a concentrated blue straggler population towards the cluster center.

No significant central concentration of cataclysmic variable candidates.

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) which were both on board the Hubble Space Telescope (HST). The FUV-UV colour-magnitude diagram (CMD) shows a main sequence (MS) turnoff at FUV $\approx$ 22 mag and FUV-UV $\approx$ 3 mag. The MS extends 4 mag below the turnoff, and a prominent horizontal branch (HB) and blue straggler (BS) sequence can be seen. A total of 1218 MS stars, 185 red giant branch stars, 47 BS stars and 41 HB stars are identified, along with 78 sources blueward of the MS which consist of white dwarfs (WDs) and objects in the gap between the WDs and the MS that include potential cataclysmic variable (CV) candidates. The radial distribution of the BS population is concentrated towards the cluster centre, indicating that mass segregation has occurred. The blue and red sub-populations of the double BS sequence appear mixed in the ultraviolet CMD, and no significant central concentration of CV candidates is seen in this cluster.