Carbon and nitrogen abundances in giant stars of the metal-poor globular cluster M15

Trefzger, D. V.; Langer, G. E.; Carbon, D. F.; Suntzeff, Nicholas B.; Kraft, Robert P.

doi:10.1086/160765

Cited by 77 publications

(108 citation statements)

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“…Both Martell et al (2008) and Briley et al (1993) suggest that this can be explained if deep mixing has produced low C/Fe ratios in bright giants of both clusters. This could well be the explanation given that a decline in the carbon abundance with increasing luminosity along the upper RGB has been observed in a number of moderate to very metal-deficient clusters, including M92 (Carbon et al 1982), M15 (Trefzger et al 1983), and M4 and NGC 6752 (Suntzeff & Smith 1991), among others. In the case of M13, even the oxygen abundance appears to follow a similar trend (Johnson & Pilachowski 2012).…”

Section: On the Retention Of Mass-loss Materials By Globular Clustersmentioning

confidence: 83%

THE AGES OF 55 GLOBULAR CLUSTERS AS DETERMINED USING AN IMPROVED $\Delta V^{\rm HB}_{\rm TO}$ METHOD ALONG WITH COLOR-MAGNITUDE DIAGRAM CONSTRAINTS, AND THEIR IMPLICATIONS FOR BROADER ISSUES

VandenBerg

Brogaard

Leaman

et al. 2013

ApJ

463

407

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Ages have been derived for 55 globular clusters (GCs) for which Hubble Space Telescope Advanced Camera for Surveys photometry is publicly available. For most of them, the assumed distances are based on fits of theoretical zero-age horizontal-branch (ZAHB) loci to the lower bound of the observed distributions of HB stars, assuming reddenings from empirical dust maps and metallicities from the latest spectroscopic analyses. The age of the isochrone that provides the best fit to the stars in the vicinity of the turnoff (TO) is taken to be the best estimate of the cluster age. The morphology of isochrones between the TO and the beginning part of the subgiant branch (SGB) is shown to be nearly independent of age and chemical abundances. For well-defined color-magnitude diagrams (CMDs), the error bar arising just from the "fitting" of ZAHBs and isochrones is ≈ ± 0.25 Gyr, while that associated with distance and chemical abundance uncertainties is ∼±1.5-2 Gyr. The oldest GCs in our sample are predicted to have ages of ≈13.0 Gyr (subject to the aforementioned uncertainties). However, the main focus of this investigation is on relative GC ages. In conflict with recent findings based on the relative main-sequence fitting method, which have been studied in some detail and reconciled with our results, ages are found to vary from mean values of ≈12.5 Gyr at [Fe/H] −1.7 to ≈11 Gyr at [Fe/H] −1. At intermediate metallicities, the age-metallicity relation (AMR) appears to be bifurcated: one branch apparently contains clusters with disk-like kinematics, whereas the other branch, which is displaced to lower [Fe/H] values by ≈0.6 dex at a fixed age, is populated by clusters with halo-type orbits. The dispersion in age about each component of the AMR is ∼±0.5 Gyr. There is no apparent dependence of age on Galactocentric distance (R G ) nor is there a clear correlation of HB type with age. As previously discovered in the case of M3 and M13, subtle variations have been found in the slope of the SGB in the CMDs of other metal-poor ([Fe/H] −1.5) GCs. They have been tentatively attributed to clusterto-cluster differences in the abundance of helium. Curiously, GCs that have relatively steep "M13-like" SGBs tend to be massive systems, located at small R G , that show the strongest evidence of in situ formation of multiple stellar populations. The clusters in the other group are typically low-mass systems (with 2-3 exceptions, including M3) that, at the present time, should not be able to retain the matter lost by mass-losing stars due either to the development of GC winds or to ram-pressure stripping by the halo interstellar medium. The apparent separation of the two groups in terms of their present-day gas retention properties is difficult to understand if all GCs were initially ∼20 times their current masses. The lowest-mass systems, in particular, may have never been massive enough to retain enough gas to produce a significant population of second-generation stars. In this case, the observed light element abundance variations, ...

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Section: On the Retention Of Mass-loss Materials By Globular Clustersmentioning

confidence: 83%

THE AGES OF 55 GLOBULAR CLUSTERS AS DETERMINED USING AN IMPROVED $\Delta V^{\rm HB}_{\rm TO}$ METHOD ALONG WITH COLOR-MAGNITUDE DIAGRAM CONSTRAINTS, AND THEIR IMPLICATIONS FOR BROADER ISSUES

VandenBerg

Brogaard

Leaman

et al. 2013

ApJ

463

407

View full text Add to dashboard Cite

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“…However, C and N inhomogeneities have been detected in GCs with metallicity comparable to the kinematic substructure in Scl dSph, both in stars fainter and brighter than the RGB bump. In M 15 ([Fe/H] = -2.37 dex), stars with luminosities above the RGB bump exhibit in general weak S(λ3883) CN bands (Trefzger et al 1983), with a handful of stars having enhanced CN absorption (Langer et al 1992;Lee 2000). Cohen et al (2005) find anticorrelated ranges of C and N abundances in unvolved RGB stars in the same cluster, with large star-to-star differences in [N/Fe] abundance ratio up to 2.5 dex.…”

Section: A Disrupted Globular Cluster?mentioning

confidence: 99%

Carbon and nitrogen abundances of individual stars in the Sculptor dwarf spheroidal galaxy

Lardo

Battaglia

Pancino

et al. 2015

A&A

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We present [C/Fe] and [N/Fe] abundance ratios and CH(λ4300) and S(λ3883) index measurements for 94 red giant branch (RGB) stars in the Sculptor dwarf spheroidal galaxy from VLT/VIMOS MOS observations at a resolving power R = 1150 at 4020 Å. This is the first time that [N/Fe] abundances are derived for a large number of stars in a dwarf spheroidal. We found a trend for the [C/Fe] abundance to decrease with increasing luminosity on the RGB across the whole metallicity range, a phenomenon observed in both field and globular cluster giants, which can be interpreted in the framework of evolutionary mixing of partially processed CNO material. Both our measurements of [C/Fe] and [N/Fe] are in good agreement with the theoretical predictions for stars at similar luminosity and metallicity. We detected a dispersion in the carbon abundance at a given [Fe/H], which cannot be ascribed to measurement uncertainties alone. We interpret this observational evidence as the result of the contribution of different nucleosynthesis sources over time to a not well-mixed interstellar medium. We report the discovery of two new carbon-enhanced, metal-poor stars. These are likely the result of pollution from material enriched by asymptotic giant branch stars, as indicated by our estimates of [Ba/Fe] > +1. We also attempted a search for dissolved globular clusters in the field of the galaxy by looking for the distinctive C-N pattern of second population globular clusters stars in a previously detected, very metal-poor, chemodynamical substructure. We do not detect chemical anomalies among this group of stars. However, small number statistics and limited spatial coverage do not allow us to exclude the hypotheses that this substructure forms part of a tidally shredded globular cluster.

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“…Further, the observed constancy of the sums of C, N, and O and of Al and Mg, observed among the giants in a cluster (Smith et al 1996 ;Shetrone 1996a ;Kraft et al 1997), make it unlikely that this primordial scenario applies to the present problem. In addition, in a number of clusters such as NGC 6752 (Suntze † 1993), M92 (Carbon et al 1982), and M15 (Trefzger et al 1983), the surface carbon abundance is observed to decline with increasing stellar luminosities along the giant branch, a fact that lends support to the "" evolutionary ÏÏ scenario that holds that the abundance anomalies are the result of processes internal to the stars themselves. It is true that bimodal distributions of CN strengths are observed among main-sequence stars and subgiants in 47 Tuc (Cannon et al 1998 and references therein), NGC 6752, M5 (Suntze † & Smith 1991), and M71 (Cohen 1999b).…”

Section: Introductionmentioning

confidence: 95%

Flash‐assisted Deep Mixing in Globular Cluster Red Giants

Aikawa

Fujimoto

Katō

2001

ApJ

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We discuss a new model of deep mixing in red giants caused by shell Ñashes triggered by the inward penetration of hydrogen into the helium core. The objective is to explain the large star-to-star variations of proton-capture elements that are observed among globular cluster red giants (Fujimoto, Aikawa, & Kato). The characteristics of this mixing model are explored by computing the products of nucleosynthesis during hydrogen shell Ñashes in red giants. It is shown that, during sufficiently strong Ñashes, both 24Mg and 23Na are depleted by burning. For moderately and very metal-poor clusters, the burned 24Mg is converted mostly into 27Al. Thus, the model not only resolves the difficulties arising from the observed underabundance of 24Mg, but also removes the problem of sodium overproduction, which would otherwise accompany the aluminum enrichment observed. For moderately metal-poor cluster giants, 25Mg and 26Mg survive with nearly scaled-solar abundances, while for very metal-poor cluster giants, all the magnesium isotopes are depleted and aluminum also burns appreciably into 28Si. For metal-rich cluster giants, shell Ñashes are quenched before 25Mg and 26Mg can burn to synthesize aluminum. These properties agree well with the manner in which observed abundance anomalies vary with cluster metallicity, including the absence of large Al-enrichments for red giants in metal-rich clusters. From a detailed comparison with observed abundances in M13 giants, we deduce constraints on the strength of the mixing mechanism responsible for the inward penetration of hydrogen into the helium core. We discuss further implications of the present results, in particular the importance of star-star interactions for the proper understanding of the evolution of stars in globular clusters.

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Carbon and nitrogen abundances in giant stars of the metal-poor globular cluster M15

Cited by 77 publications

References 0 publications

THE AGES OF 55 GLOBULAR CLUSTERS AS DETERMINED USING AN IMPROVED $\Delta V^{\rm HB}_{\rm TO}$ METHOD ALONG WITH COLOR-MAGNITUDE DIAGRAM CONSTRAINTS, AND THEIR IMPLICATIONS FOR BROADER ISSUES

THE AGES OF 55 GLOBULAR CLUSTERS AS DETERMINED USING AN IMPROVED $\Delta V^{\rm HB}_{\rm TO}$ METHOD ALONG WITH COLOR-MAGNITUDE DIAGRAM CONSTRAINTS, AND THEIR IMPLICATIONS FOR BROADER ISSUES

Carbon and nitrogen abundances of individual stars in the Sculptor dwarf spheroidal galaxy

Flash‐assisted Deep Mixing in Globular Cluster Red Giants

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