Abstract:
We report the discovery of four blue lurkers with low- and extremely low mass white dwarf (ELM WD) companions in the
Galactic globular cluster NGC 362 using AstroSat’s Ultra Violet Imaging Telescope (UVIT). We analysed the multiwavelength
spectral energy distribution (SED) of far-ultraviolet-bright main-sequence stars using data from the UVIT, Ultraviolet Optical
Telescope, Gaia EDR3, and 2.2-m ESO/MPI telescopes. Two each of low-mass WDs and ELM WDs are found as companions
for the four blue lurkers by the fitting of two-component SED models. The effective temperatures, radii, luminosities, and masses
of two low-mass WDs are (35 000, 23 000) K, (0.04, 0.05) R , (1.45, 0.22) L , and (0.2, 0.2) M , while the two ELM WDs
are (14 750, 14 750) K, (0.09, 0.10) R , (0.34, 0.40) L , and (0.18, 0.18) M , respectively. The position of blue lurkers within
the cluster shows that they originated via the Case A/B mass-transfer mechanism in a low-density environment. This is the first
detection of blue lurkers with low-mass WDs and ELM WDs as companions in a globular cluster. The companion’s cooling age
is less than 4 Myr, which suggests that they were just recently formed. These binary systems might have originated due to the
cluster’s recent core collapse.
