A double stellar generation in the globular cluster  NGC 6656 (M 22)

Marino, A. F.; Milone, A. P.; Piotto, G.; Villanova, S.; Bedin, L. R.; Bellini, Andrea; Renzini, A.

doi:10.1051/0004-6361/200911827

Cited by 260 publications

(445 citation statements)

References 44 publications

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“…In this case, the observational evidence comes from the split of the SGB (Milone et al 2008). There are other GCs which undoubtedly show a split in the SGB, like NGC 6388 (Moretti et al 2009), M 22 (Piotto 2009;Marino et al 2009), 47 Tuc ), which also shows a MS broadening, or in the RGB, like M4 (Marino et al 2008). Recent investigations (Rich et al 2004;Faria et al 2007) suggest that also other galaxies might host GCs with more than one population of stars.…”

Section: Introductionmentioning

confidence: 99%

Radial distribution of the multiple stellar populations in $\mathsf{\omega}$ Centauri

Bellini

Piotto

Bedin

et al. 2009

A&A

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114

109

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Aims. We present a detailed study of the radial distribution of the multiple populations identified in the Galactic globular cluster ω Cen. Methods. We used both space-based images (ACS/WFC and WFPC2) and ground-based images (FORS1@VLT and WFI@2.2m ESO telescopes) to map the cluster from the inner core to the outskirts (∼20 arcmin). These data sets have been used to extract high-accuracy photometry for the construction of color−magnitude diagrams and astrometric positions of ∼900 000 stars. Results. We find that in the inner ∼2 core radii the blue main sequence (bMS) stars slightly dominate the red main sequence (rMS) in number. At greater distances from the cluster center, the relative numbers of bMS stars with respect to rMS drop steeply, out to ∼8 arcmin, and then remain constant out to the limit of our observations. We also find that the dispersion of the Gaussian that best fits the color distribution within the bMS is significantly greater than the dispersion of the Gaussian that best fits the color distribution within the rMS. In addition, the relative number of intermediate-metallicity red-giant-branch stars (which includes the progeny of the bMS) with respect to the metal-poor component (the progeny of the rMS) follows a trend similar to that of the main-sequence star-count ratio N bMS /N rMS . The most metal-rich component of the red-giant branch follows the same distribution as the intermediatemetallicity component. Conclusions. We briefly discuss the possible implications of the observed radial distribution of the different stellar components in ω Cen.

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Section: Introductionmentioning

confidence: 99%

Radial distribution of the multiple stellar populations in $\mathsf{\omega}$ Centauri

Bellini

Piotto

Bedin

et al. 2009

A&A

Self Cite

114

109

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“…Globular clusters (GCs) host mono-metallic 1 , almost coeval stellar populations that have been studied extensively, both ⋆ E-mail: angelou@mps.mpg.de 1 with a few exceptions, such as e.g., Omega Cenaturi (Johnson & Pilachowski 2010), M22 (Marino et al 2009), M54 (Carretta et al 2010a), M2 (Yong et al 2014) photometrically and spectroscopically. In spite of their multiple populations (see Gratton, Carretta & Bragaglia 2012), these systems offer well constrained tests for stellar evolution theory.…”

Section: Introductionmentioning

confidence: 99%

Diagnostics of stellar modelling from spectroscopy and photometry of globular clusters

Angelou

D’Orazi

Constantino

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We conduct a series of comparisons between spectroscopic and photometric observations of globular clusters and stellar models to examine their predictive power. Data from medium-to-high resolution spectroscopic surveys of lithium allow us to investigate first dredge-up and extra mixing in two clusters well separated in metallicity. Abundances at first dredge-up are satisfactorily reproduced but there is preliminary evidence to suggest that the models overestimate the luminosity at which the surface composition first changes in the lowest-metallicity system. Our models also begin extra mixing at luminosities that are too high, demonstrating a significant discrepancy with observations at low metallicity. We model the abundance changes during extra mixing as a thermohaline process and determine that the usual diffusive form of this mechanism cannot simultaneously reproduce both the carbon and lithium observations. Hubble Space Telescope photometry provides turnoff and bump magnitudes in a large number of globular clusters and offers the opportunity to better test stellar modelling as function of metallicity. We directly compare the predicted main-sequence turn-off and bump magnitudes as well as the distance-independent parameter ∆M V MSTO bump . We require 15 Gyr isochrones to match the main-sequence turn-off magnitude in some clusters and cannot match the bump in low-metallicity systems. Changes to the distance modulus, metallicity scale and bolometric corrections may impact on the direct comparisons but ∆M V MSTO bump , which is also underestimated from the models, can only be improved through changes to the input physics. Overshooting at the base of the convective envelope with an efficiency that is metallicity dependent is required to reproduce the empirically determined value of ∆M V MSTO bump .

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“…Secondly, a star-to-star dispersion in iron-peak elements, and other elements, has long been known to exist in the globular cluster ω Centauri (e.g., Freeman & Rodgers 1975;Cohen 1981;Norris & Da Costa 1995;Smith et al 2000;Johnson & Pilachowski 2010). More recently, abundance dispersions have also been identified in a number of globular clusters including M2 , M22 (Marino et al 2009Roederer et al 2011), M54 (Carretta et al 2010a) Carretta et al 2011), NGC 3201 1 (Simmerer et al 2013), NGC 5824 2 ) and Terzan 5 (Ferraro et al 2009;Origlia et al 2013), although the shape of the metallicity distribution function differs between these objects.…”

Section: Introductionmentioning

confidence: 99%

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

Yong¹,

Grundahl²,

Norris³

2014

Monthly Notices of the Royal Astronomical Society

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We measure the C+N+O abundance sum in red giant stars in two Galactic globular clusters, NGC 1851 and NGC 6752. NGC 1851 has a split subgiant branch which could be due to different ages or C+N+O content while NGC 6752 is representative of the least complex globular clusters. For NGC 1851 and NGC 6752, we obtain average values of A(C+N+O) = 8.16 ± 0.10 (σ = 0.34) and 7.62 ± 0.02 (σ = 0.06), respectively. When taking into account the measurement errors, we find a constant C+N+O abundance sum in NGC 6752. The C+N+O abundance dispersion is only 0.06 dex, and such a result requires that the source of the light element abundance variations does not increase the C+N+O sum in this cluster. For NGC 1851, we confirm a large spread in C+N+O. In this cluster, the anomalous RGB has a higher C+N+O content than the canonical RGB by a factor of four (∼0.6 dex). This result lends further support to the idea that the two subgiant branches in NGC 1851 are roughly coeval, but with different CNO abundances.

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A double stellar generation in the globular cluster NGC 6656 (M 22)

Cited by 260 publications

References 44 publications

Radial distribution of the multiple stellar populations in $\mathsf{\omega}$ Centauri

Radial distribution of the multiple stellar populations in $\mathsf{\omega}$ Centauri

Diagnostics of stellar modelling from spectroscopy and photometry of globular clusters

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

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