Light-element abundance variations in the Milky Way halo

Martell, Sarah L.; Grebel, Eva K.

doi:10.1051/0004-6361/201014135

Cited by 143 publications

(167 citation statements)

References 71 publications

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“…On the other hand, Na-rich and O-poor stars that are common in GCs are rare among field stars (Carretta et al) and are possibly absent from open clusters (OCs, see e.g., de Silva et al 2009). A similar result is obtained for other light elements, such as C and N, see e.g., Martell & Smith (2009), Martell & Grebel (2010). The onset of the mechanism that leads to the multiple stellar population phenomenon is tied to the dynamics of the star formation process and has in turn to depend on many variables such as age, metallicity, total mass, and probably also on the environment (e.g., position in the Galaxy or in a smaller galaxy) where the cluster formed.…”

Section: Introductionmentioning

confidence: 70%

Searching for multiple stellar populations in the massive, old open cluster Berkeley 39

Bragaglia

Gratton

Carretta

et al. 2012

A&A

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The most massive star clusters include several generations of stars with a different chemical composition (mainly revealed by an Na-O anti-correlation) while low-mass star clusters appear to be chemically homogeneous. We are investigating the chemical composition of several clusters with masses of a few 10 4 M to establish the lower mass limit for the multiple stellar population phenomenon. Using VLT/FLAMES spectra we determine abundances of Fe, O, Na, and several other elements (α, Fe-peak, and neutron-capture elements) in the old open cluster Berkeley 39. This is a massive open cluster: M ∼ 10 4 M , approximately at the border between small globular clusters and large open clusters. Our sample size of about 30 stars is one of the largest studied for abundances in any open cluster to date, and will be useful to determine improved cluster parameters, such as age, distance, and reddening when coupled with precise, well-calibrated photometry. We find that Berkeley 39 is slightly metal-poor, [Fe/H] = −0.20, in agreement with previous studies of this cluster. More importantly, we do not detect any star-to-star variation in the abundances of Fe, O, and Na within quite stringent upper limits. The rms scatter is 0.04, 0.10, and 0.05 dex for Fe, O, and Na, respectively. This small spread can be entirely explained by the noise in the spectra and by uncertainties in the atmospheric parameters. We conclude that Berkeley 39 is a single-population cluster.

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Section: Introductionmentioning

confidence: 70%

Searching for multiple stellar populations in the massive, old open cluster Berkeley 39

Bragaglia

Gratton

Carretta

et al. 2012

A&A

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“…But the question of how many field halo stars come from disrupted GCs is still under debate (e.g. Yong et al 2008;Boley et al 2009;Martell & Grebel 2010;Carretta et al 2010). Recently, Jordi & Grebel (2010) detected tidal features using the same data set as this study.…”

Section: Consequencesmentioning

confidence: 80%

The age of the Milky Way halo stars from the Sloan Digital Sky Survey

Jofré

Weiß

2011

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We determined the age of the stellar content of the Galactic halo by considering main-sequence turn-off stars. From the large number of halo stars provided by Sloan Digital Sky Survey, we could accurately detect the turn-off as a function of metallicity of the youngest dominant population, which was done by looking at the hottest (bluest) stars of a population. Using the turn-off temperature of a population of a given metallicity, we looked for the isochrones with that turn-off temperature and metallicity and found no age gradient as a function of metallicity. This would mean that this dominating population of the Galactic halo formed rapidly, probably during the collapse of the proto-Galactic gas. Moreover, we could find a significant number of stars with hotter temperatures than the turn-off, which might be blue horizontal branch (BHB) stars, blue stragglers, or main sequence stars that are younger than the dominant population and were probably formed in external galaxies and accreted later on to our Milky Way. Motivated by the current debate about the efficiency of gravitational settling (atomic diffusion) in the interior of old solar-type stars, we used isochrones with and without settling to determine the ages. When ignoring diffusion in the isochrones we obtained ages of 14−16 Gyr. This result is a strong argument against inhibited diffusion in old halo field stars, since it results in a serious conflict with the age of the Universe of 13.7 Gyr. The age obtained including diffusion in the isochrones was 10−12 Gyr, which agrees with the absolute age of the old globular clusters in the inner halo.

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“…Stars resembling globular cluster second generation stars have been found in the halo (Martell & Grebel 2010) and their eventual presence in the bulge might gauge the role that globular clusters had, through losing stars and/or disintegrating in the formation of the bulge. However, Martell & Grebel (2010) have not analysed O, Na, Mg, and Al, so it is still to be proved whether their sample indeed originated from globular clusters. Also, a connection with the globular cluster O-Na anti-correlation for MOA-2009-BLG-259S and MOA-2010-BLG-523S is unlikely given that their O, Na, Al, and Mg abundances are all high (and several other elements too for one of the two stars).…”

Section: The Metal-rich Bulgementioning

confidence: 99%