Detection of young massive white dwarfs in core-collapsed globular cluster NGC 362

Abstract

Core-collapsed globular clusters are ideal targets to explore the presence of stellar collision products. Here, we have studied 17 far-UV bright white dwarf (WD) members in the globular cluster NGC 362 using data obtained from the Ultra Violet Imaging Telescope (UVIT) mounted on AstroSat and from the Hubble Space Telescope. Multiwavelength spectral energy distributions (SEDs) are analyzed using UV and optical data sets to characterize and determine the parameters of WDs. Fourteen of the WDs fit single-component SEDs well, while three showed a good fit with a two-component SED model, indicating a binary system comprising a WD and a low-mass main-sequence (MS) star. The effective temperatures, radii, luminosities, and masses of WDs are in the ranges 22,000–70,000 K, 0.008–0.028 R⊙, 0.09–3.0 L⊙, and 0.30–1.13 M⊙, respectively. The effective temperatures, radii, luminosities, and masses of the companions (low-mass MS stars) are 3500–3750 K, 0.150–0.234 R⊙, 0.003–0.01 L⊙, and 0.14–0.24 M⊙, respectively. The three binary systems (WD-MS), along with the massive WDs, may have formed through dynamical processes that occurred during the core collapse of the cluster. This is the first evidence of a massive WD formation in a core-collapsed cluster, which is the missing link in the formation of a fast radio burst (FRB) progenitor in a globular cluster. This study provides evidence that NGC 362 hosts stellar systems that may evolve into exotic stars such as Type Ia supernovae and/or FRBs in the future. This Letter is paper VI of the Globular Cluster UVIT Legacy Survey.