Abstract Details

Name: Sindhu Pandey
Affiliation: Aryabhatta Research Institute of Observational Sciences
Conference ID: ASI2021_283
Title : Multiwavelength study of old open clusters: NGC 188 and M67
Authors and Co-Authors : Sindhu Pandey (Aryabhatta Research Institute of Observational Sciences), Annapurni Subramaniam (Thesis Supervisor, Indian Institute of Astrophysics), C Anuradha (Thesis Supervisor, Vellore Institute of Technology)
Abstract Type : Oral
Abstract Category : Thesis
Abstract : The thesis focuses on understanding the single and binary stellar evolution in the old open clusters, M67 and NGC 188 using multiwavelength photometric data. We have used images from the Ultra-Violet Imaging Telescope (UVIT) on ASTROSAT, the first Indian space observatory and combined them with other photometric data from 0.14-11.5 µm wavelength range and spectra in the ultraviolet (UV) range. In NGC188, using the first light data of UVIT, we have discovered a hot companion to a blue straggler star (BSS). The estimated fundamental parameters of the components suggest that the BSS is formed as a result of a recent mass transfer (MT) from a post AGB/HB star. A deep UV study of the M67 was performed using GALEX images to reveal the presence of a large number of stars with far-UV (FUV) and/or near-UV (NUV) excess. Some of these stars were found to be in binaries and many are single stars. These indicate that a large number of Sun like stars in this cluster may be chromospherically active. We detect a few main-sequence + white dwarf (MS+WD) binaries in M67, which could be progenitors of Cataclysmic variables. We created multiwavelength spectral energy distributions (SED)s of 45 interesting candidates and estimated their fundamental parameters. We classified BSSs into three groups and suggest that they are formed between 400 Myr - 2 Gyr, more or less continuously. The multi-filter FUV images of M67 from UVIT were used to study 9 bright BSSs. The SEDs of 6 BSSs were found not to fit well with single star spectra, but fitted well with a hot + cool composite spectra, consistent with IUE and HST spectra. The estimated parameters suggest the hot companions to be WDs, and this is the first confirmed detection of WD companions to BSSs in M67.