Search for Candle Stars in Globular Clusters: Spectroscopic Analysis of Post-AGB Candidates

Jasniewicz, G.; Parthasarathy, M.

doi:10.1007/978-3-540-76961-3_10

Cited by 2 publications

(1 citation statement)

References 4 publications

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“…A very rough estimate based on the comparison of the intensity peak with stars of known magnitudes suggest that this star is brighter than the cluster RGB tip and may have a color as blue as (B − V) 0 ≈ 0.0. This would be consistent with a Post Asymptotic Giant Branch star (Jasniewicz & Parthasarathy 2009), that may well dominate the UV flux of the cluster. Hence, B337 may be the example of a cluster whose integrated UV-optical color is strongly affected by fore/back-ground contamination and/or by a rare non-HB source.…”

Section: Smi Vs (Fuv -V ) 0 : the Effect Of Blue Tailssupporting

confidence: 74%

The horizontal branch morphology of M 31 globular clusters

Bellazzini

Buzzoni

Cacciari

et al. 2012

A&A

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We use deep, high quality color magnitude diagrams obtained with the Hubble Space Telescope to compute a simplified version of the Mironov index (SMI; B B+R ) to parametrize the horizontal branch (HB) morphology for 23 globular clusters in the M 31 galaxy (Sample A), all located in the outer halo at projected distances between 10 kpc and 100 kpc. This allows us to compare them with their Galactic counterparts, for which we estimated the SMI exactly in the same way, in the SMI vs. [Fe/H] plane. We find that the majority of the considered M 31 clusters lie in a significantly different locus, in this plane, with respect to Galactic clusters lying at any distance from the center of the Milky Way. In particular they have redder HB morphologies at a given metallicity, or, in other words, clusters with the same SMI value are ≈0.4 dex more metal rich in the Milky Way than in M 31. We discuss the possible origin of this difference and we conclude that the most likely explanation is that many globular clusters in the outer halo of M 31 formed ≈1-2 Gyr later than their counterparts in the outer halo of the Milky Way, while differences in the cluster-to-cluster distribution of He abundance of individual stars may also play a role. The analysis of another sample of 25 bright M 31 clusters (eighteen of them with M V ≤ −9.0, Sample B), whose SMI estimates are much more uncertain as they are computed on shallow color magnitude diagrams, suggests that extended blue HB tails can be relatively frequent among the most massive M 31 globular clusters, possibly hinting at the presence of multiple populations.

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Section: Smi Vs (Fuv -V ) 0 : the Effect Of Blue Tailssupporting

confidence: 74%

The horizontal branch morphology of M 31 globular clusters

Bellazzini

Buzzoni

Cacciari

et al. 2012

A&A

View full text Add to dashboard Cite

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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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Search for Candle Stars in Globular Clusters: Spectroscopic Analysis of Post-AGB Candidates

Cited by 2 publications

References 4 publications

The horizontal branch morphology of M 31 globular clusters

The horizontal branch morphology of M 31 globular clusters

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

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