Two Distinct Red Giant Branch Populations in the Globular Cluster NGC 2419 as Tracers of a Merger Event in the Milky Way

Lee, Young-Wook; Han, Sang-Il; Joo, Seok-Joo; Jang, Sang Ho; Na, Chongsam; Okamoto, Sakurako; Arimoto, N.; Lim, Dongwook; Kim, Hak-Sub; Yoon, Suk-Jin

doi:10.1088/2041-8205/778/1/l13

Cited by 31 publications

(35 citation statements)

References 31 publications

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“…Marino et al (2012b) found that the populations of M 22, characterized by different metallicities, are almost coeval within ∼ 300 Myr. Lee et al (2013) found that the GC NGC 2419 hosts two populations characterized by a large difference in [Fe/H], Y and with a relative age of about 2 Gyr. Roh et al (2011) compared models and CMDs of NGC 288 to put constraints on the second stellar population hosted by this GC.…”

Section: Discussionmentioning

confidence: 99%

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters – IV. Helium content and relative age of multiple stellar populations within NGC 6352★

Nardiello

Piotto

Milone

et al. 2015

Monthly Notices of the Royal Astronomical Society

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In this paper we combine WFC3/UVIS F275W, F336W, and F438W data from the "UV Legacy Survey of Galactic Globular Clusters: Shedding Light on Their Populations and Formation" (GO 13297) HST Treasury program with F606W, F625W, F658N, and F814W ACS archive data for a multi-wavelength study of the globular cluster NGC 6352. In the colormagnitude and two-color diagrams obtained with appropriate combination of the photometry in the different bands we separate two distinct stellar populations and trace them from the main sequence to the subgiant, red giant, horizontal and asymptotic giant branches.We infer that the two populations differ in He by ∆Y = 0.029±0.006. With a new method, we also estimate the age difference between the two sequences. Assuming no difference in [Fe/H] and [α/Fe], and the uncertainties on ∆Y, we found a difference in age between the two populations of 10 ± 120 Myr. If we assume [Fe/H] and [α/Fe] differences of 0.02 dex (well within the uncertainties of spectroscopic measurements), the total uncertainty in the relative age rises to ∼300 Myr.

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Section: Discussionmentioning

confidence: 99%

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters – IV. Helium content and relative age of multiple stellar populations within NGC 6352★

Nardiello

Piotto

Milone

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…Photometry of NGC 2419 provides evidence for a spread in the initial helium abundance of the cluster stars. Lee at al. (2013) inferred that the red giant branch is split into two distinct subpopulations, with 70% of the stars showing a primordial helium abundance and the other 30% showing helium mass fractions near 0.42, corresponding to an enhancement of ∆Y ≈ 0.19.…”

Section: Heliummentioning

confidence: 99%

On Potassium and Other Abundance Anomalies of Red Giants in NGC 2419

Iliadis

Karakas

Prantzos

et al. 2016

ApJ

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Globular clusters are of paramount importance for testing theories of stellar evolution and early galaxy formation. Strong evidence for multiple populations of stars in globular clusters derives from observed abundance anomalies. A puzzling example is the recently detected Mg-K anticorrelation in NGC 2419. We perform Monte Carlo nuclear reaction network calculations to constrain the temperature-density conditions that gave rise to the elemental abundances observed in this elusive cluster. We find a correlation between stellar temperature and density values that provide a satisfactory match between simulated and observed abundances in NGC 2419 for all relevant elements (Mg, Si, K, Ca, Sc, Ti, and V). Except at the highest densities (ρ 10 8 g/cm 3 ), the acceptable conditions range from ≈ 100 MK at ≈ 10 8 g/cm 3 to ≈ 200 MK at ≈ 10 −4 g/cm 3 . This result accounts for uncertainties in nuclear reaction rates and variations in the assumed initial composition. We review hydrogen burning sites and find that low-mass stars, AGB stars, massive stars, or supermassive stars cannot account for the observed abundance anomalies in NGC 2419. Super-AGB stars could be viable candidates for the polluter stars if stellar model parameters can be fine-tuned to produce higher temperatures. Novae, either involving CO or ONe white dwarfs, could be interesting polluter candidates, but a current lack of low-metallicity nova models precludes firmer conclusions. We also discuss if additional constraints for the firstgeneration polluters can be obtained by future measurements of oxygen, or by evolving models of second-generation low-mass stars with a non-canonical initial composition.

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“…In particular, isochrone fitting of high-precision photometric data for a handful of GCs calls for relatively low helium enrichment between +0.01 and +0.2 in mass fraction (∆Y) 1 among MSPs; the highest values are derived for those GCs that exhibit the most extended O-Na anticorrelations and that are among the most massive within the Milky Way (e.g. Piotto et al 2007;Busso et al 2007;Caloi & D'Antona 2007;King et al 2012;Milone et al 2012bMilone et al , 2013Milone 2015;Lee et al 2013;Bellini et al 2017). The lowest values for He enrichment are hard to reconcile with the FRMS and the AGB scenarios which both require a minimum ∆Y of ∼0.13-0.15 to reproduce the bulk abundance variations, while higher values are needed to account for the most extreme part of the O-Na anticorrelation (see Bastian et al 2015;Chantereau et al 2016;and Chantereau et al 2017, for extended discussions of the various issues raised by the He constraints).…”

Section: Introductionmentioning

confidence: 99%

Revisiting nucleosynthesis in globular clusters

Prantzos

Charbonnel

Iliadis

2017

A&A

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Context. Motivated by recent reports concerning the observation of limited enrichment in He but excess K in stars of globular clusters, we revisit the H-burning conditions that lead to the chemical properties of multiple stellar populations in these systems. Aims. In particular, we are interested in correlations of He and K with other elements, such as O, Na, Al, Mg and Si, reported in stars of NGC 2808. Methods. We performed calculations of nucleosynthesis at constant temperature and density, exploring the temperature range of 25 to 200 × 10 6 K (25 to 200 MK), using a detailed nuclear reaction network and the most up-to-date nuclear reaction rates. Results. We find that Mg is the most sensitive "thermometer" of hydrostatic H-burning conditions, pointing to a temperature range of 70-80 MK for NGC 2808, while He is a lesser -but not negligible -constraint. Potassium can be produced at the levels reported for NGC 2808 at temperatures >180 MK and Si at T > 80 MK. However, in the former temperature range Al and Na are totally destroyed and no correlation can be obtained, in contrast to the reported observations. None of the putative polluter sources proposed so far seem to satisfy the ensemble of nucleosynthesis constraints.

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Two Distinct Red Giant Branch Populations in the Globular Cluster NGC 2419 as Tracers of a Merger Event in the Milky Way

Cited by 31 publications

References 31 publications

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters – IV. Helium content and relative age of multiple stellar populations within NGC 6352★

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters – IV. Helium content and relative age of multiple stellar populations within NGC 6352★

On Potassium and Other Abundance Anomalies of Red Giants in NGC 2419

Revisiting nucleosynthesis in globular clusters

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