UOCS. IV. Discovery of diverse hot companions to blue stragglers in the
  old open cluster King 2
  King 2, one of the oldest clusters in the Milky Way, with an age of $\sim$ 6
Gyr and distance of $\sim 5700$ pc, has been observed with UVIT payload on the
\textit{ASTROSAT}. With membership information derived from {\it Gaia} EDR3,
the cluster is found to have 39 blue straggler stars (BSSs). We created
multi-wavelength spectra-energy distributions (SED) of all the BSSs. Out of 10
UV detected BSSs, 6 bright ones fitted with double component SEDs and were
found to have hotter companions with properties similar to extreme horizontal
branch (EHB)/subdwarf B (sdB) stars, with a range in luminosity and
temperature, suggesting a diversity among the hot companions. We suggest that
at least 15\% of BSSs in this cluster are formed via mass-transfer pathway.
When we compared their properties to EHBs and hotter companions to BSS in open
and globular clusters, we suggest that EHB/sdBs like companions can form in
binaries of open clusters as young as 6 Gyr.
