• CHAYAN MONDAL

      Articles written in Journal of Astrophysics and Astronomy

    • UOCS. V. UV study of the old open cluster NGC 188 using AstroSat

      SHARMILA RANI ANNAPURNI SUBRAMANIAM SINDHU PANDEY SNEHALATA SAHU CHAYAN MONDAL GAJENDRA PANDEY

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      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.

    • A tale of two nearby dwarf irregular galaxies WLM and IC 2574: As revealed by UVIT

      CHAYAN MONDAL ANNAPURNI SUBRAMANIAM KOSHY GEORGE

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      We present an ultra-violet study of two nearby dwarf irregular galaxies WLM and IC 2574, using the Far-UV and Near-UV data from the Ultra-Violet Imaging Telescope (UVIT). We used the F148W band Far-UV images and identified 180 and 782 young star-forming clumps in WLM and IC 2574, respectively. The identified clumps have sizes between 7–30 pc in WLM and 26–150 pc in IC 2574. We noticed more prominent hierarchical splitting in the structure of star-forming regions at different flux levels in IC 2574 than WLM. We found that the majority of the clumps have elongated shapes in the sky plane with ellipticity ($\varepsilon$) greater than 0.6 in both the galaxies. The major axis of the identified clumps is found to show no specific trend of orientation in IC 2574, whereas in WLM the majority are aligned along south-west to north-east direction. We estimated (F148W–N242W) colour for the clumps identified in WLM and noticed that theyounger ones (with (F148W–N242W) < $-$ 0:5) are smaller in size (<10 pc) and are located mostly in the southern half of the galaxy between galactocentric radii 0.4–0.8 kpc.

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