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Upcoming Seminar/Colloqium

Topic:

UVIT/AstroSat study of three old open clusters: M 67, King 2 and NGC 188

Speaker : Sindhu Pandey
Affiliation : ARIES, Nainital
Date & Time :
Venue : Auditorium and zoom
Abstract :

In the series of Ultra Violet Imaging Telescope (UVIT on AstroSat) study of Open clusters (UOCS), here we investigate the stellar populations in three old open clusters: M67, King 2 and NGC 188. In M67, we detected low to extremely low mass (LM/ELM) white dwarfs (WDs) companions to four blue stragglers (BSSs) (WOCS2013, WOCS3013, WOCS4006, and WOCS5005), using Far-UV (FUV) photometry obtained in two epochs from UVIT. We speculate three possible formation pathways - their orbits are altered due to cluster dynamics, some may be in triple systems with LM/ELM WDs in an unknown closer orbit, or a modified mass transfer mechanism may be required to enable their formation. In King 2, we detected hot companions to six of ten BSSs simultaneously observed in two UV filters. We characterize the hot companions to have properties similar to extreme horizontal branch (HB)/sub-dwarf B stars, with a range in temperature and luminosity, suggesting diversity among the hot companions. We suggest that at least 15 % of BSSs in this cluster are formed via mass transfer. In NGC 188, we have constructed UV- optical colour magnitude diagrams using a combination of UVIT (two FUV and one near-UV (NUV)) filters with optical V band photometry. In the FUV images, we detect only hot and bright BSSs, one hot sub-dwarf, and one WD candidate. In the NUV images, we detect members up to 22 mag including 21 BSSs, two yellow straggler stars and one WD candidate. We find the cluster to have HB population with three stars in the temperature range of 4750 to 21000 K.

About Speaker :

Dr. Sindhu Pandey is a postdoc at ARIES. This seminar is part of her annual progress evaluation.