Ultraviolet stellar population of the old open cluster M67 (NGC 2682)
  We present the results of ultraviolet (UV) photometry of the old open cluster
M67 obtained using Galaxy Evolution Explorer (GALEX) in far-ultraviolet (FUV)
and near-ultraviolet (NUV) bands. UV detections of 18 blue straggler stars
(BSSs), 3 white dwarfs (WDs), 4 yellow straggler stars, 2 sub-subgiants, and 25
X-ray sources are presented (along with an online catalog). We demonstrate the
capability of UV colour magnitude diagrams (CMDs) along with the UV isochrones
to identify potential stars which defy standard stellar evolution in this well
studied cluster. We also detect a few main sequence turn-off and subgiant
branch stars with excess flux in the FUV and/or NUV. UV continuum excess as
well as Mg II $\it h$ +$\it k$ emission lines from the IUE archival spectra for
2 red giants are detected, suggestive of their chromospheric activity. We
suggest that a large number of stars in this cluster are chromospherically
active, whereas the bright BSS are unlikely to be active. We also estimate the
fundamental parameters L/L$_{\odot}$, R/R$_{\odot}$ and T$_{eff}$ of the BSSs
and 15 FUV bright stars by constructing the spectral energy distribution (SED)
using multi-wavelength data. We identify three groups among the BSSs, based on
their properties. The H-R diagram of BSSs with isochrones suggests that the
BSSs in M67 are formed in the last 2.5 Gyr - 400 Myr, more or less
continuously. We identify 7 potential MS+WD candidates based on large UV excess
from a probable 11, based on SEDs.
