Study of UV bright stellar populations in the globular cluster NGC 1261 using AstroSat

Abstract

We present the UV photometry of the globular cluster NGC 1261 using images acquired with the Ultraviolet Imaging Telescope (UVIT) on-board ASTROSAT. We performed PSF photometry on four near-UV (NUV) and two far-UV (FUV) images and constructed UV colour-magnitude diagrams (CMDs), in combination with HST, Gaia, and ground-based optical photometry for member stars. We detected the full horizontal branch (HB) in NUV, blue HB in the FUV and identified two extreme HB (EHB) stars. HB stars have a tight sequence in UV-optical CMDs well-fitted with isochrones generated (12.6 Gyr age, [Fe/H] = -1.27 metallicity) using updated BaSTI-IAC models. Effective temperatures (Teff), luminosities and radii of bright HB stars were estimated using spectral energy distribution. As we detect the complete sample of UV bright HB stars, the hot end of the HB distribution is found to terminate at the G-jump (Teff ~ 11500 K). The two EHB stars, fitted well with single spectra, have Teff= 31,000 K and a mass = 0.495Msun and follow the same Teff-Radius relation of the blue HB stars. We constrain the formation pathways of these EHB stars to extreme mass loss in the RGB phase (either due to rotation or enhanced Helium), OR early hot-flash scenario.

arXiv comment13 pages, 9 figures, 3 tables, Accepted for publication in MNRAS

References in corpus (79)

• The NumPy array: a structure for efficient numerical computation
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• Correcting for the Effects of Interstellar Extinction
• The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
• K-corrections and filter transformations in the ultraviolet, optical, and near infrared
• A large stellar evolution database for population synthesis studies. I. Scaled solar models and isochrones
• The propagation of uncertainties in stellar population synthesis modeling III: model calibration, comparison, and evaluation
• The Wavelength Dependence of Interstellar Extinction from 1.25 to 8.0 microns Using GLIMPSE Data
• Global survey of star clusters in the Milky Way II. The catalogue of basic parameters
• A Triple Main Sequence in the Globular Cluster NGC 2808
• Intrinsic iron spread and a new metallicity scale for Globular Clusters
• Gaia Data Release 2: Kinematics of globular clusters and dwarf galaxies around the Milky Way
• VOSA: Virtual Observatory SED Analyzer. An application to the Collinder 69 open cluster
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• The Ages of 55 Globular Clusters as Determined Using an Improved delta V_TO^HB Method Along with Color-Magnitude Diagram Constraints, and Their Implications for Broader Issues
• The ACS Survey of Galactic Globular Clusters. IX. Horizontal Branch Morphology and the Second Parameter Phenomenon
• Metallicities on the Double Main Sequence of omega Centauri Imply Large Helium Enhancement
• Variable Stars in Galactic Globular Clusters
• Post-Asymptotic Giant Branch Evolution of Low- and Intermediate-Mass Stars. Preliminary Results
• New models for the evolution of Post-Asymptotic Giant Branch stars and Central Stars of Planetary Nebulae
• Spectroscopic and Photometric evidence of two stellar populations in the Galactic Globular Cluster NGC6121 (M4)
• Hot subluminous stars
• The Updated BaSTI Stellar Evolution Models and Isochrones: I. Solar Scaled Calculations
• Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
• A helium spread among the main sequence stars in NGC 2808
• The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851
• Helium variation due to self-pollution among Globular Cluster stars: consequences on the horizontal branch morphology
• The Origin of Extreme Horizontal Branch Stars
• Hot Horizontal-Branch Stars: The Ubiquitous Nature of the "Jump" in Stromgren u, Low Gravities, and the Role of Radiative Levitation of Metals
• In-orbit Calibrations of the Ultra-Violet Imaging Telescope
• Super Helium-Rich Population and the Origin of Extreme Horizontal-Branch Stars in Globular Clusters
• Flash Mixing on the White Dwarf Cooling Curve: Understanding Hot Horizontal Branch Anomalies in NGC 2808
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters - XVII. Public Catalogue Release
• Can Planets Influence the Horizontal Branch Morphology?
• Ultraviolet Radiation from Evolved Stellar Populations: II. The Ultraviolet Upturn Phenomenon in Elliptical Galaxies
• An abundance analysis of bright giants in the globular cluster NGC 1851
• Enrichment by supernovae in globular clusters with multiple populations
• Hubble Space Telescope reveals multiple Sub-Giant Branch in eight Globular Clusters
• Ruprecht 106: the first single population Globular Cluster?
• Blue Straggler Stars: a direct comparison of Star counts and population ratios in six Galactic Globular Clusters
• Mixed Populations in Globular Clusters: Et Tu, 47 Tuc?
• Multimodal Distributions along the Horizontal Branch
• The Peculiar Horizontal Branch Morphology of the Galactic Globular Clusters NGC 6388 and NGC 6441: new insights from UV observations
• Global and non-global parameters of horizontal branch morphology of globular clusters
• The peculiar Horizontal Branch of NGC 2808
• First full evolutionary computation of the He-flash induced mixing in Population II stars
• The Horizontal Branch in the UV Colour Magnitude Diagrams. II. The case of M3, M13 and M79
• Hot Stars in Globular Cluster - A Spectroscopist's View
• Blue Straggler Stars in the Unusual Globular Cluster NGC 6388
• HST Observations of New Horizontal Branch Structures in the Globular Cluster omega Centauri
• In-orbit Performance of UVIT and First Results
• The ubiquitous nature of the Horizontal Branch second U-jump: A link with the Blue Hook scenario?
• A New Feature Along the Extended Blue Horizontal Branch of NGC 6752
• The lack of close binaries among hot horizontal branch stars in NGC6752
• Abundance analyses of cool extreme helium stars
• The effect of helium-enhanced stellar populations on the ultraviolet-upturn phenomenon of early-type galaxies
• UV Properties of Galactic Globular Clusters with GALEX I. The Color-Magnitude Diagrams
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. VII. Implications from the Nearly Universal Nature of Horizontal Branch Discontinuities
• The "UV-route" to search for Blue Straggler Stars in Globular Clusters: first results from the HST UV Legacy Survey
• The Blue Hook Populations of Massive Globular Clusters
• In-orbit Performance of UVIT on ASTROSAT
• A lack of close binaries among hot horizontal branch stars in globular clusters - M80 and NGC5986
• A lack of close binaries among hot horizontal branch stars in globular clusters. II. NGC\,2808
• A Far-UV Survey of M 80: X-ray Source Counterparts, Strange Blue Stragglers and the Recovery of Nova T Sco
• Hot UV-bright stars of galactic globular clusters
• Constraints on the Formation of the Globular Cluster IC 4499 from Multi-Wavelength Photometry
• A possible formation channel for blue hook stars in globular cluster
• The Horizontal Branch population of NGC 1851 as revealed by the Ultra-violet Imaging Telescope (UVIT)
• Wide-field multi-color photometry of the Galactic globular cluster NGC 1261
• Extraction of globular clusters members with Gaia DR2 astrometry
• Formation and Evolution of Blue Stragglers in 47 Tucanae
• G2C2 - IV: A novel approach to study the radial distributions of multiple populations in Galactic globular clusters
• Far-Ultraviolet Observation of the Globular Cluster NGC 6397
• An AO-assisted variability study of four globular clusters
• Blue Hook Stars in Globular Clusters
• UVIT-HST-GAIA view of NGC 288: A census of hot stellar population and their properties from UV
• UV-Bright Stellar Populations and Their Evolutionary Implications in the Collapsed-Core Cluster M15
• A possible physical connection between helium-rich stellar populations of massive globular clusters and the UV upturn of galactic spheroids
• NGC 1261: A time-series \emph{VI} study of its variable stars

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