Abstract:
Blue metal-poor (BMP) stars are the main-sequence stars that appear bluer and more luminous than normal turn-off stars of
metal-poor globular clusters. They are believed to be either field blue straggler stars (FBSS) formed via post-mass transfer
mechanism or accreted from dwarf satellite galaxies of the Milky Way. A significant fraction of BMP stars are discovered to
be potential binaries. We observed 27 BMP stars using UVIT/AstroSat in two FUV filters, F148W and F169M. We report the
discovery of white dwarf (WD) companions of 12 BMP stars for the first time. The WD companions have estimated temperatures
Teff ∼10 500–18 250 K, and masses 0.17–0.8 M. Based on [Fe/H] and space velocity, we group the 12 BMP/FBSS stars as the
thick disc (5) and halo (5), whereas two stars appear to be in-between. All the 5 thick disc BMP/FBSS have extremely low-mass
(M < 0.2 M) WDs as companions, whereas the 5 halo BMP/FBSS have low (0.2 M < M < 0.4 M), normal (0.4 M < M
< 0.6 M), and high mass (M > 0.6 M) WD companions. Our analysis suggests that at least ∼44 per cent of BMP stars are
FBSS, and these stars hold the key to understand the details of mass transfer, binary properties, and chemical enrichment among
the FBSS
