UVIT/ASTROSAT studies of Blue Straggler stars and post-mass transfer systems in star clusters: Detection of one more blue lurker in M67

TL;DR

This study uses UVIT/ASTROSAT observations to identify a new blue lurker star with an ELM white dwarf companion in M67, providing insights into post-mass transfer binary evolution in star clusters.

Contribution

The paper reports the detection of an additional blue lurker with an ELM WD in M67, expanding understanding of post-mass transfer systems and their characteristics in star clusters.

Findings

Detection of a new blue lurker with an ELM WD in M67.

Correlation between WD temperature and BSS rotational velocity.

Presence of a normal WD in BSS+WD system in NGC 5466.

Abstract

The blue straggler stars (BSSs) are main-sequence (MS) stars, which have evaded stellar evolution by acquiring mass while on the MS. The detection of extremely low mass (ELM) white dwarf (WD) companions to two BSSs and one yellow straggler star (YSS) from our earlier study using UVIT/ASTROSAT, as well as WD companions to main-sequence stars (known as blue lurkers) suggest a good fraction of post-mass transfer binaries in M67. Using deeper UVIT observations, here we report the detection of another blue lurker in M67, with an ELM WD companion. The post-mass transfer systems with the presence of ELM WDs, including BSSs, are formed from Case A/B mass transfer and are unlikely to show any difference in surface abundances. We find a correlation between the temperature of the WD and the $v\ sin i$ of the BSSs. We also find that the progenitors of the massive WDs are likely to belong to the hot and luminous group of BSSs in M67. The only detected BSS+WD system by UVIT in the globular cluster NGC 5466, has a normal WD and suggests that open cluster like environment might be present in the outskirts of low density globular clusters.