Evolved stars in globular clusters

Globular clusters (GCs) are gravitaionally bound systems of hundreds of stars. These systems are good laboratories to study stellar evolution as the stars are “believed” to be of the same chemical composition and age. In our work, we use observations from the ultraviolet photometric instrument UVIT on-board the ASTR0SAT to study evolved (post-red-giant) stars.

UVIT, and its UV sensitivity makes it a useful instrument to study evolved stars. It somewhat segregates the UV bright stars, usually evolved stars in old systems like the GCs. Further, the resolution of UVIT is better than other contemporary UV-photometric missions.

Comparision of resolution of UVIT (left) and GALEX (right).

Colour-Magnitude diagrams (CMD) of NGC 7492 (left) and E3 (right) using UVIT photometric filters.

We also follow-up interesting targets (Kumar et al., 2024). with spectroscopy (optical currently) to measure abundances, and radial velocities. This is to constrain any peculiar evolutionary characteristics or check the nature of their multiplicity, if any.

The star in red is a post-AGB star showing third dredge-up (3DU) CNO abundances, similar to the stars in blue. The black stars show no enchancement/3DU.

Possible binary models for an evolved star which shows shifts in radial velocities (black dots).

References

2024