UV photometry of spotted stars in the horizontal branch of the globular
  cluster NGC 2808 using AstroSat
  A recent study of hot (20,000 to 30,000 K) extreme horizontal branch (EHB)
stars in globular clusters (GCs) has led to the discovery of their variability.
It is suggested that this variability is driven by the projected rotation of
magnetic spots on the stellar surfaces and is expected to have higher
amplitudes at shorter wavelengths. Here, we present the analysis of such hot
stars in the massive GC NGC 2808 using the Ultraviolet Imaging Telescope
(UVIT), aboard AstroSat. We use the UVIT data in combination with the Hubble
Space Telescope UV Globular Cluster Survey (HUGS) data for the central region
(within $\sim$ $2.7'$ $\times$ $2.7'$) and ground-based optical photometry for
the outer parts of the cluster. We generate the far-UV (FUV) - optical
colour-magnitude diagrams (CMDs) and in these we find a population of hot EHB
stars fainter than the zero-age horizontal branch (ZAHB) model. A comparison of
our FUV magnitudes of the already reported variable EHB stars (vEHBs) shows
that the longest period vEHBs are the faintest, along with a tentative
correlation between rotation period and UV magnitude of spotted stars. In order
to firmly establish any correlation, further study is essential.
