Laksh Gupta, BS (Honours) in Physics, Class of 2024

Supervisor: Professor Samyaday Choudhury, School of Arts and Sciences

Thesis Brief

NGC2808 is a very intriguing and unusual galactic globular cluster that purportedly has undergone more than one episode of star formation, hosting distinct stellar subpopulations. In this study, the white dwarf (WD) stars in NGC 2808 have been analysed using near-ultraviolet and optical data (F275W, F336W, and F438W) from the Hubble Space Telescope. The identification and studies of various types of WDs - e.g. ones with a core composed of carbon and oxygen (CO-core) and ones with a core composition of helium (He-core) are crucial for understanding their formation scenario, which remains elusive and could depend on factors like binarity, cluster mass, etc. In this study, the colour-magnitude diagrams of NGC2808 using various combinations of filters and theoretical models of WD cooling sequences were used to identify WDs. Star counts of the main sequence turnoff stars and red giant branch stars were performed, and artificial star test results were used to correct their completeness. These were then compared with the WDs to constrain the number of WDs in the cluster. This is needed to understand the formation scenario of He-core WDs since such stars supposedly form through binary interactions for the Universe’s ∼ 13 billion-year history.