CNO abundances in the globular clusters NGC 1851 and NGC 6752★

Yong, David; Grundahl, F.; Norris, John E.

doi:10.1093/mnras/stu2334

Cited by 75 publications

(85 citation statements)

References 100 publications

(113 reference statements)

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“…Because of low abundances, most of these elements, excluding CNO sum, have only negligible effect on stellar models (see, e.g., VandenBerg et al 2012). Some GCs, such as NGC 1851 (Yong et al 2015), are reported to contain CNO enhanced stars, but more observations are needed to confirm the ubiquity of these stars in GCs and bulge fields. Jang et al (2014) have shown that some mild CNO enhancement (∆Z CNO ≈ 0.0003), in addition to helium enhancement, would be required to best reproduce the Oosterhoff dichotomy among halo GCs and G1 (G2/G1=0.54) is also well reproduced, if the observed ratio is defined from the peak positions on the histogram showing a period distribution (see Figure 15 of Pietrukowicz et al 2015).…”

Section: 012)mentioning

confidence: 99%

Common Origin of Two Rr Lyrae Populations and the Double Red Clump in the Milky Way Bulge

Lee

Jang

2016

ApJ

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A recent survey toward the Milky Way bulge has discovered two sequences of RR Lyrae stars on the period-amplitude diagram with a maximum period-shift of ∆log P ≈ 0.015 between the two populations. Here we show, from our synthetic horizontal-branch models, that this periodshift is most likely due to the small difference in helium abundance (∆Y = 0.012) between the first and second-generation stars (G1 and G2), as is the case in our models for the inner halo globular clusters with similar metallicity ([Fe/H] ≈ -1.1). We further show that the observed double red clump (RC) in the bulge is naturally reproduced when these models are extended to solar metallicity following ∆Y/∆Z ≈ 6 for G2, as would be expected from the chemical evolution models. Therefore, the two populations of RR Lyrae stars and the double RC observed in the bulge appear to be different manifestations of the same multiple population phenomenon in the metal-poor and metal-rich regimes respectively.

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Section: 012)mentioning

confidence: 99%

Common Origin of Two Rr Lyrae Populations and the Double Red Clump in the Milky Way Bulge

Lee

Jang

2016

ApJ

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“…Amongst its peculiarities is a double sub-giant branch in the colour-magnitude diagram (Milone et al 2008). Other anomalies include a range in C+N+O abundance among the cluster red giants (Yong et al 2009;Ventura et al 2009;Yong, Grundahl & Norris 2015, and references therein), and star-to-star variations in [Fe/H] and s-process elements (Yong & Grundahl 2008;Carretta et al 2010;Gratton et al 2012). The two sub-giant branch populations correlate with the observed abundance variations, as the brighter sub-giant branch is metal-poor and under-abundant in s-process elements compared to the fainter sub-giant population.…”

Section: Introductionmentioning

confidence: 99%

The outer envelopes of globular clusters. II. NGC 1851, NGC 5824 and NGC 1261*

Kuzma

Costa

Mackey

2017

Monthly Notices of the Royal Astronomical Society

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We present a second set of results from a wide-field photometric survey of the environs of Milky Way globular clusters. The clusters studied are NGC 1261, NGC 1851 and NGC 5824: all have data from DECam on the Blanco 4m telescope. NGC 5824 also has data from the Magellan Clay telescope with MegaCam. We confirm the existence of a large diffuse stellar envelope surrounding NGC 1851 of size at least 240 pc in radius. The radial density profile of the envelope follows a power-law decline with index γ = −1.5 ± 0.2 and the projected shape is slightly elliptical. For NGC 5824 there is no strong detection of a diffuse stellar envelope, but we find the cluster is remarkably extended and is similar in size (at least 230 pc in radius) to the envelope of NGC 1851. A stellar envelope is also revealed around NGC 1261. However, it is notably smaller in size with radius ∼105 pc. The radial density profile of the envelope is also much steeper with γ = −3.8 ± 0.2. We discuss the possible nature of the diffuse stellar envelopes, but are unable to draw definitive conclusions based on the current data. NGC 1851, and potentially NGC 5824, could be stripped dwarf galaxy nuclei, akin to the cases of ω Cen, M54 and M2. On the other hand, the different characteristics of the NGC 1261 envelope suggest that it may be the product of dynamical evolution of the cluster.

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“…Elements whose surface abundance is particularly sensitive to this phenomenon include the light elements Li, Be, B, C (in particular the ratio of C12/C13), and N; C and N are measured by surveys such as APOGEE. There is also evidence, especially in metal-poor stars, for changes in CNO abundances along the giant branch (e.g., Kraft 1994;Yong et al 2015), which requires a mixing process not usually included in standard models whose origin is still uncertain (Angelou et al 2012). However, empirical correlations between stars of known mass and surface abundances can yield powerful insights even without detailed knowledge of the underlying physics.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic Determination of Masses (And Implied Ages) for Red Giants

Ness

Hogg

Rix

et al. 2016

ApJ

229

296

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The mass of a star is arguably its most fundamental parameter. For red giant stars, tracers luminous enough to be observed across the Galaxy, mass implies a stellar evolution age. It has proven to be extremely difficult to infer ages and masses directly from red giant spectra using existing methods. From the Kepler and APOGEE surveys, samples of several thousand stars exist with high-quality spectra and asteroseismic masses. Here we show that from these data we can build a data-driven spectral model using TheCannon, which can determine stellar masses to ∼0.07 dex from APOGEE DR12 spectra of red giants; these imply age estimates accurate to ∼0.2 dex (40%). We show that TheCannon constrains these ages foremost from spectral regions with CN absorption lines, elements whose surface abundances reflect mass-dependent dredge-up. We deliver an unprecedented catalog of 70,000 giants (including 20,000 red clump stars) with mass and age estimates, spanning the entire disk (from the Galactic center toR 20 kpc). We show that the age information in the spectra is not simply a corollary of the birth-material abundances

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CNO abundances in the globular clusters NGC 1851 and NGC 6752★

Cited by 75 publications

References 100 publications

Common Origin of Two Rr Lyrae Populations and the Double Red Clump in the Milky Way Bulge

Common Origin of Two Rr Lyrae Populations and the Double Red Clump in the Milky Way Bulge

The outer envelopes of globular clusters. II. NGC 1851, NGC 5824 and NGC 1261*

Spectroscopic Determination of Masses (And Implied Ages) for Red Giants

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