Spectroscopy of giants in LMC clusters. I - Velocities, abundances, and the age-metallicity relation

Olszewski, Edward W.; Schommer, R. A.; Suntzeff, Nicholas B.; Harris, Hugh C.

doi:10.1086/115701

Cited by 269 publications

(445 citation statements)

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“…Results are presented in Table 1. For LE8, Olszewski et al (1991) give a velocity of 248 ± 5 km s −1 , in excellent agreement with our value. The mean velocity of all investigated AGB stars in NGC 1846 is 248 ± 5.5 km s −1 , which is in good agreement with the published values for the cluster.…”

Section: Cluster Membershipsupporting

confidence: 91%

AGB stars of the intermediate-age LMC cluster NGC 1846

Lebzelter¹,

Lederer²,

Cristallo

et al. 2008

A&A

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Aims. We investigate the change in the surface abundance of 12 C during the evolution along the AGB, aiming to constrain third dredge-up models. Methods. High-resolution, near-infrared spectra of a sample of AGB stars in the LMC cluster NGC 1846 were obtained. A cluster sample ensures a high level of homogeneity with respect to age, metallicity, and distance. The C/O ratio and the ratio of 12 C/ 13 C were measured and compared with our evolutionary models. Results. For the first time, we show the evolution of the C/O and 12 C/ 13 C ratios along a cluster AGB. Our findings allow us to check the reliability of the evolutionary models and, in particular, the efficiency of the third dredge up. The increase in both C/O and 12 C/ 13 C in the observed O-rich stars is reproduced by the models well. However, the low carbon isotopic ratios of the two C-stars in our sample indicate the late occurrence of moderate extra mixing. The extra mixing affects the most luminous AGB stars and is capable of increasing the abundance of 13 C, while leaving unchanged the C/O ratio, which has been fixed by the cumulative action of several third dredge-up episodes. We find indications that the F abundance also increases along the AGB, supporting an in situ production of this element.

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Section: Cluster Membershipsupporting

confidence: 91%

AGB stars of the intermediate-age LMC cluster NGC 1846

Lebzelter¹,

Lederer²,

Cristallo

et al. 2008

A&A

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“…Olsen et al 1998;Mackey & Gilmore 2003), integrated optical spectroscopy, and spectra of individual giant stars (e.g. Olszewski et al 1991;Beasley et al 2002;Johnson et al 2006;Mucciarelli et al 2008). We can also benefit from near-IR studies, both imaging and spectroscopy, of the giant stars in these clusters (e.g.…”

Section: Sample Selection and Observational Strategymentioning

confidence: 99%

“…So far, studies of the stellar populations have been made mainly with photometric methods (e.g. Frogel et al 1990;Dirsch et al 2000;Mucciarelli et al 2006;Mackey et al 2008), and two bright cluster stars have been observed by Olszewski et al (1991) to spectroscopically estimate the metallicity of the cluster (see Table 1). Moreover, there is neither information about its dynamical properties in the literature, nor information about its bounds.…”

Section: Intermediate Age Clustersmentioning

confidence: 99%

IntegratedK-band spectra of old and intermediate-age globular clusters in the Large Magellanic Cloud

Lyubenova

Küntschner²,

Rejkuba

et al. 2010

A&A

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Current stellar population models have arguably the largest uncertainties in the near-IR wavelength range, partly due to a lack of large and well calibrated empirical spectral libraries. In this paper we present a project whose aim it is to provide the first library of luminosity weighted integrated near-IR spectra of globular clusters to be used to test the current stellar population models and serve as calibrators for future ones. Our pilot study presents spatially integrated K-band spectra of three old (≥10 Gyr) and metal poor ([Fe/H] ∼ −1.4), and three intermediate age (1-2 Gyr) and more metal rich ([Fe/H] ∼ −0.4) globular clusters in the LMC. We measured the line strengths of the Na i, Ca i and 12 CO (2-0) absorption features. The Na i index decreases with increasing age and decreasing metallicity of the clusters. The D CO index, used to measure the 12 CO (2-0) line strength, is significantly reduced by the presence of carbon-rich TP-AGB stars in the globular clusters with age ∼1 Gyr. This is in contradiction to the predictions of the stellar population models of Maraston (2005, MNRAS, 362, 799). We find that this disagreement is due to the different CO absorption strength of carbon-rich Milky Way TP-AGB stars used in the models and the LMC carbon stars in our sample. For globular clusters with age ≥2 Gyr we find D CO index measurements consistent with the model predictions.

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“…Spectra in the z-band region of giant stars were obtained with FORS2 at the ESO/VLT observatory to measure metallicities based on absorption lines of the Ca ii triplet (CaT). We employ the "reduced equivalent width" method first introduced by Olszewski et al (1991) and Armandroff & Da Costa (1991, hereafter AD91), which is the same as used in R97. One caveat with this method is that α-elements (which include Ca) are enhanced in GGCs compared to the solar value, with [α/Fe] ∼ +0.3 (e.g.…”

Section: Introductionmentioning

confidence: 99%

Homogeneous metallicities and radial velocities for Galactic globular clusters

Saviane

Costa

Held

et al. 2012

A&A

203

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Well determined radial velocities and abundances are essential for analyzing the properties of the globular cluster system of the Milky Way. However more than 50% of these clusters have no spectroscopic measure of their metallicity. In this context, this work provides new radial velocities and abundances for twenty Milky Way globular clusters which lack or have poorly known values for these quantities. The radial velocities and abundances are derived from spectra obtained at the Ca ii triplet using the FORS2 imager and spectrograph at the VLT, calibrated with spectra of red giants in a number of clusters with well determined abundances. For about half of the clusters in our sample we present significant revisions of the existing velocities or abundances, or both. We also confirm the existence of a sizable abundance spread in the globular cluster M 54, which lies at the center of the Sagittarius dwarf galaxy. In addition evidence is provided for the existence of a small intrinsic internal abundance spread (σ[Fe/H] int ≈ 0.11−0.14 dex, similar to that of M 54) in the luminous distant globular cluster NGC 5824. This cluster thus joins the small number of Galactic globular clusters known to possess internal metallicity ([Fe/H]) spreads.

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Spectroscopy of giants in LMC clusters. I - Velocities, abundances, and the age-metallicity relation

Cited by 269 publications

References 0 publications

AGB stars of the intermediate-age LMC cluster NGC 1846

AGB stars of the intermediate-age LMC cluster NGC 1846

IntegratedK-band spectra of old and intermediate-age globular clusters in the Large Magellanic Cloud

Homogeneous metallicities and radial velocities for Galactic globular clusters

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