UVIT observations of UV-Bright stars in four Galactic Globular Clusters

Kumar, Ranjan; Pradhan, Ananta C.; Parthasarathy, M.; Ojha, D. K.; Mohapatra, Abhisek; Murthy, Jayant

doi:10.1017/s1743921319007373

Proc. IAU

2019

DOI: 10.1017/s1743921319007373

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UVIT observations of UV-Bright stars in four Galactic Globular Clusters

Ranjan Kumar¹,

Ananta C. Pradhan²,

M. Parthasarathy

et al.

Abstract: We have performed photometric analysis of four Galactic globular clusters (GGCs): NGC 4147, NGC 4590, NGC 5053 and NGC 7492 using far-UV and near-UV filters of the Ultraviolet Imaging Telescope (UVIT) on-board AstroSat. With the help of color-magnitude diagrams (CMDs), we have identified ∼ 150 blue horizontal branch stars (BHBs), and ∼ 40 blue straggler stars (BSS) in the four GGCs. We study the temperature and radial distribution of BHBs and BSS for the four GGCs.

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

et al. 2021

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We present far ultraviolet (FUV) observations of globular cluster NGC 4147 using three FUV filters, BaF 2 (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 using proper 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, we identify 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 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.

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

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Ultraviolet Imaging Telescope (UVIT) observation of the Galactic globular cluster NGC 7492

Kumar

Pradhan

Mohapatra

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We present detailed photometric observations of the Galactic globular cluster NGC 7492 using the data obtained with two far-ultraviolet (FUV; 1300–1800 Å) and three near-ultraviolet (NUV; 2000–3000 Å) filters of Ultraviolet Imaging Telescope (UVIT) onboard the AstroSat satellite. We confirmed the cluster membership of the extracted sources using Gaia data release 2 (Gaia DR2) proper motion data. We have used colour–magnitude diagrams (CMDs) using UVIT and GAIA filters to separate out different evolutionary stages of the stars present in the cluster. We have identified a new extreme horizontal branch (EHB) star at the core of the cluster using UV and UV-optical CMDs. The estimated distance modulus of the cluster is 16.95 ± 0.05 obtained by fitting BaSTI isochrones with cluster parameters, [Fe/H] = −1.8 dex and age =12.0 Gyr on the V − I versus V CMD. Interestingly, only the EHB star and blue horizontal branch stars (BHBs) among the UV-bright hot sources are detected in FUV filters of UVIT. We have derived the effective temperature of BHBs using colour–temperature relation and spectral energy distributions (SEDs) of multiband filters, which are in the range from 8000 to 10 500 K. We find a variation of He abundance of BHBs by fitting the BaSTI ZAHB (zero-age horizontal branch). The range in the He abundance of the BHBs corresponding to the best-fitting isochrones is from 0.247 to 0.350. We have estimated various physical parameters of the newly identified EHB star in the cluster using SED fit and post-HB evolutionary tracks. We have studied the radial distribution of all the sources of the cluster detected in UVIT. The sources detected in FUV filters extend beyond the half-light radius (1.15 arcmin) of the cluster, whereas the sources detected in NUV filters extend beyond the tidal radius (9.2 arcmin) of the cluster.

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UVIT observations of UV-Bright stars in four Galactic Globular Clusters

Cited by 2 publications

References 20 publications

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

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

Ultraviolet Imaging Telescope (UVIT) observation of the Galactic globular cluster NGC 7492

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