• RANJAN KUMAR

      Articles written in Journal of Astrophysics and Astronomy

    • UVIT study of UV bright stars in the globular cluster NGC 4147

      RANJAN KUMAR ANANTA C. PRADHAN MUDUMBA PARTHASARATHY DEVENDRA K. OJHA ABHISEK MOHAPATRA JAYANT MURTHY SANTI CASSISI

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      We present far ultraviolet (FUV) observations of globular cluster NGC 4147 using three FUV filters, BaF2 (F154W), sapphire (F169M), and silica (F172M) of Ultra-Violet Imaging Telescope (UVIT) onboard the AstroSat satellite. We confirmed the cluster membership of the UVIT observed sources usingproper motions from Gaia data release 2 (GAIA DR2). We identified 37 blue horizontal branch stars (BHBs), one blue straggler star (BSS) and 15 variable stars using UV-optical color magnitude diagrams (CMDs). We find that all the FUV bright BHBs are second generation population stars. Using UV-optical CMDs, weidentify two sub-populations, BHB1 and BHB2, among the UV-bright BHBs in the cluster with stars count ratio of 24:13 for BHB1 and BHB2. The effective temperatures ($T_{\rm eff}$) of BHB1 and BHB2 were derived using color-temperature relation of BaSTI-IAC zero-age horizontal branch (ZAHB). We found that BHB1 stars are more centrally concentrated than BHB2 stars. We also derive physical parameters of the detected FUV bright BSS by fitting younger age BaSTI-IAC isochrones on optical and UV-optical CMDs.

    • Study of Galactic structure using UVIT/AstroSat star counts

      RANJAN KUMAR ANANTA C. PRADHAN DEVENDRA K. OJHA SONIKA PIRIDI TAPAS BAUG S. K. GHOSH

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      The structure of our Galaxy has been studied from ultraviolet (UV) star counts obtained with the Ultra-Violet Imaging Telescope (UVIT) on board the AstroSat satellite, in Far-UV (FUV) and Near-UV (NUV) bands. The F154W (BaF$_2$) and N263M (NUVB4) filters were used in the FUV and NUV bands,respectively. The point sources are separated from the extra-galactic sources of UVIT observations using infrared (IR) color cut method. The observed UVIT star counts match well with the simulations obtained from the Besanc¸on model of stellar population synthesis towards several Galactic directions. We alsoestimated the scale length and scale height of the thick disc and the scale height of the thin disc using the space density function and the exponential density law for the stars of intermediate galactic latitudes. The scale length of the thick disc ranges from 3.11 to 5.40 kpc whereas the scale height ranges from $530 \pm 32$ pc to $630 \pm 29$ pc. The scale height of the thin disc comes out to be in the range of $230 \pm 20$ pc to $330 \pm 11$ pc.

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