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      https://www.ias.ac.in/article/fulltext/joaa/042/0047

    • Keywords

       

      Galaxy: open clusters: individual: NGC 188; stars: horizontal-branch; stars: blue stragglers; stars: Hertzsprung–Russell and colour-magnitude diagrams.

    • Abstract

       

      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.

    • Author Affiliations

       

      SHARMILA RANI1 2 ANNAPURNI SUBRAMANIAM1 SINDHU PANDEY3 SNEHALATA SAHU1 CHAYAN MONDAL1 GAJENDRA PANDEY1

      1. Indian Institute of Astrophysics, Koramangala II Block, Bengaluru 560 034, India.
      2. Pondicherry University, R.V. Nagar, Kalapet 605 014, India.
      3. Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital 263 001, India.
    • Dates

       
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