We present the UV photometry of the old open cluster NGC188 obtained using images acquired with Ultraviolet Imaging Telescope (UVIT) on board the AstroSat satellite, in two far-UV (FUV) and one near-UV (NUV) filters. UVIT data is utilised in combination with optical photometric data to construct the optical and UV colour-magnitude diagrams (CMDs). In the FUV images, we detect only hot and bright blue straggler stars (BSSs), one hot subdwarf, and one white dwarf (WD) candidate. In the NUV images, we detect members up to a faintness limit of $\sim$22 mag including 21 BSSs, 2 yellow straggler stars (YSSs), and one WD candidate. This study presents the first NUV-optical CMDs, and are overlaid with updated BaSTIIAC isochrones and WD cooling sequence, which are found to fit well to the observed CMDs. We use spectral energy distribution (SED) fitting to estimate the effective temperatures, radii, and luminosities of the UV-bright stars. We find the cluster to have an HB population with three stars ($T_{\rm eff}=4750–21000$ K). We also detect two yellow straggler stars, with one of them with UV excess connected to its binarity and X-ray emission.

We present the study of dynamical status of the globular cluster NGC 1851. A combination of multi-wavelength space and ground-based data sets are used for the present analysis. In order to select the genuine cluster members, we used the astro-photometric data available from HST and GAIA-DR2 catalogs. The BSS radial distribution of the cluster is plotted from the center of the cluster to the outskirts. The radial distribution of BSS shows a central peak, followed by a dip at the intermediate radii ($r_{\rm min}\sim 90''$) and a rising trend in the outskirts. We also estimated $A^+_{rh}$ parameter as $0.391 \pm 0.006$ to validate the findings of the radial distribution study. On the basis of the minima in the BSS radial distribution and the value of $A^+_{rh}$ parameter, we conclude that NGC 1851 belongs to Family II classification and is an intermediate dynamical statecluster.

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 atshorter 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 thanthe 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 anycorrelation, further study is essential.