Bayesian analysis of two stellar populations in Galactic globular clusters– III. Analysis of 30 clusters

Wagner-Kaiser, R.; Stenning, David C.; Sarajedini, Ata; Hippel, Ted von; Dyk, David A. van; Robinson, Elliot; Stein, Nathan; Jefferys, W. H.

doi:10.1093/mnras/stw2247

Cited by 20 publications

(16 citation statements)

References 65 publications

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“…Milone et al 2012;Piotto et al 2013;Milone 2015). Based on current samples, the fraction of second populations stars and their helium enrichment appears to vary significantly in different clusters (with 0.01 < ∆Y < 0.12) and may correlate with cluster mass (Wagner-Kaiser et al 2016;Milone et al 2017). The combination of first population stars and helium enhanced second population stars can help to explain the complex HB star morphologies observed in the Galactic globular clusters (e.g.…”

Section: Introductionmentioning

confidence: 85%

Hubble Space Telescope FUV observations of M31’s globular clusters suggest a spatially homogeneous helium-enriched subpopulation

Peacock

Zepf

Maccarone

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We present high spatial resolution, far ultraviolet (FUV) F140LP observations of 12 massive globular clusters in M 31 obtained using the ACS/SBC on the Hubble Space Telescope (HST). These observations resolve the cluster profiles to scales similar to their core radii and enable the study of the spatial distribution of blue and extreme horizontal branch (HB) stars, which dominate the emission in the F140LP images. We confirm that some of these clusters have excess FUV emission, suggesting additional hot populations beyond those expected by canonical single stellar populations models. We find no evidence that the hot populations are spatially distinct from the majority populations in these clusters, as would be expected if the excess FUV emission is a result of a dynamically enhanced population of extreme-HB stars. We conclude that a second population of stars with significantly enhanced helium abundance is a viable explanation for the observed FUV emission which is both bright and distributed similarly to the rest of the cluster light. Our results support the use of FUV observations as a path to characterising helium enhanced sub populations in extragalactic clusters. These M31 clusters also show a correlation such that more massive and denser clusters are relatively FUV bright. Similar to extant Milky Way results, this may indicate the degree of helium enrichment, or second population fraction increases with cluster mass.

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Section: Introductionmentioning

confidence: 85%

Hubble Space Telescope FUV observations of M31’s globular clusters suggest a spatially homogeneous helium-enriched subpopulation

Peacock

Zepf

Maccarone

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…Furthermore, other works based on HST data (Dalessandro et al 2014;Piotto et al 2015;Milone et al 2017) and high-resolution spectroscopy (Mucciarelli et al 2016) demonstrated that NGC 6362 hosts multiple stellar populations. Since NGC 6362 is one of the analyzed clusters in De Angeli et al (2005), Meissner & Weiss (2006), Marín-Franch et al (2009), Dotter et al (2010, Paust et al (2010), VandenBerg et al (2013 and Wagner-Kaiser et al (2016, it is a key comparison object for the present paper. It was identified as one of the oldest Galactic GCs by Marín-Franch et al (2009), Paust et al (2010), VandenBerg et al (2013 and Wagner-Kaiser et al (2016.…”

Section: Introductionmentioning

confidence: 99%

Ages of the Bulge Globular Clusters NGC 6522 and NGC 6626 (M28) from HST Proper-motion-cleaned Color–Magnitude Diagrams*

Kerber

Nardiello

Ortolani

et al. 2018

ApJ

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Bulge globular clusters (GCs) with metallicities [Fe/H]−1.0 and blue horizontal branches are candidates to harbor the oldest populations in the Galaxy. Based on the analysis of HST proper-motion-cleaned color-magnitude diagrams in filters F435W and F625W, we determine physical parameters for the old bulge GCs NGC 6522 and NGC 6626 (M28), both with well-defined blue horizontal branches. We compare these results with similar data for the inner halo cluster NGC 6362. These clusters have similar metallicities (−1.3[Fe/H]−1.0) obtained from high-resolution spectroscopy. We derive ages, distance moduli, and reddening values by means of statistical comparisons between observed and synthetic fiducial lines employing likelihood statistics and the Markov chain Monte Carlo method. The synthetic fiducial lines were generated using α-enhanced BaSTI and Dartmouth stellar evolutionary models, adopting both canonical (Y∼0.25) and enhanced (Y∼0.30-0.33) helium abundances. RR Lyrae stars were employed to determine the HB magnitude level, providing an independent indicator to constrain the apparent distance modulus and the helium enhancement. The shape of the observed fiducial line could be compatible with some helium enhancement for NGC 6522 and NGC 6626, but the average magnitudes of RR Lyrae stars tend to rule out this hypothesis. Assuming canonical helium abundances, BaSTI and Dartmouth models indicate that all three clusters are coeval, with ages between ∼12.5 and 13.0 Gyr. The present study also reveals that NGC 6522 has at least two stellar populations, since its CMD shows a significantly wide subgiant branch compatible with 14%±2% and 86%±5% for first and second generations, respectively.

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“…Here, we are adopting that the 1G stars have primordial helium content (Y), which is consistent with the literature (Bastian & Lardo 2018). Wagner-Kaiser et al (2016) performed a bayesian isochrone fitting, in the context of MPs, for a sample of 30 GCs. Differently from the present work, they fitted the value of Y for the 1G stars, resulting in some cases in a high content of Y 1G ∼ 0.30.…”

Section: Age Difference ∆τmentioning

confidence: 99%

“…On the contrary, we are interested in finding if there is an age difference between the stellar populations. Even though our approach is similar to the one applied in Wagner-Kaiser et al (2016), the methods are based on different assumptions.…”

Section: Age Difference ∆τmentioning

confidence: 99%

Self-consistent Analysis of Stellar Clusters: An Application to HST Data of the Halo Globular Cluster NGC 6752

Souza

Kerber

Barbuy

et al. 2020

ApJ

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The Bayesian isochrone fitting using the Markov chain Monte Carlo algorithm is applied, to derive the probability distribution of the parameters age, metallicity, reddening, and absolute distance modulus. We introduce the SIRIUS code by means of simulated color-magnitude diagrams, including the analysis of multiple stellar populations. The population tagging is applied from the red giant branch to the bottom of the main sequence. Through sanity checks using synthetic HST color-magnitude diagrams of globular clusters we verify the code reliability in the context of simple and multiple stellar populations. In such tests, the formal uncertainties in age or age difference, metallicity, reddening, and absolute distance modulus can reach 400 Myr, 0.03 dex, 0.01 mag, and 0.03 mag, respectively. We apply the method to analyse NGC 6752, using Dartmouth stellar evolutionary models. Assuming a single stellar population, we derive an age of 13.7 ± 0.5 Gyr and a distance of d = 4.11 ± 0.08 kpc, with the latter in agreement within 3σ with the inverse Gaia parallax. In the analysis of the multiple stellar populations, three populations are clearly identified. From the Chromosome Map and UV/Optical two-color diagrams inspection, we found a fraction of stars of 25 ± 5, 46 ± 7, and 29 ± 5 per cent, for the first, second, and third generations, respectively. These fractions are in good agreement with the literature. An age difference of 500 ± 410 Myr between the first and the third generation is found, with the uncertainty decreasing to 400 Myr when the helium enhancement is taken into account.

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Bayesian analysis of two stellar populations in Galactic globular clusters– III. Analysis of 30 clusters

Cited by 20 publications

References 65 publications

Hubble Space Telescope FUV observations of M31’s globular clusters suggest a spatially homogeneous helium-enriched subpopulation

Hubble Space Telescope FUV observations of M31’s globular clusters suggest a spatially homogeneous helium-enriched subpopulation

Ages of the Bulge Globular Clusters NGC 6522 and NGC 6626 (M28) from HST Proper-motion-cleaned Color–Magnitude Diagrams*

Self-consistent Analysis of Stellar Clusters: An Application to HST Data of the Halo Globular Cluster NGC 6752

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