The stellar content of the Hamburg/ESO survey

Schörck, T.; Christlieb, N.; Cohen, Jason Blake; Beers, Timothy C.; Shectman, Steve; Thompson, I. B.; McWilliam, Andrew; Bessell, M. S.; Norris, John E.; Meléndez, Jorge; Ramírez, Solange; Haynes, Dionne; Cass, Paul; Hartley, M.; Russell, Ken; Watson, Fred; Zickgraf, F. J.; Behnke, B.; Fechner, C.; Fuhrmeister, B.; Barklem, P. S.; Edvardsson, B.; Frebel, Anna; Wisotzki, L.; Reimers, D.

doi:10.1051/0004-6361/200810925

Cited by 128 publications

(189 citation statements)

References 72 publications

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“…The abundances seem to indicate that this RR Lyrae star is a rather normal halo star at [Fe/H] = −0.9, placing it in the more metal-rich tail of the halo metallicity distribution (Schörck et al 2009). However, the metallicity also matches the moderately metal-poor stars in the bulge, where Li et al (2015) recently found 19 candidate HVSs could originate from; for more details see Sects.…”

Section: Stellar Parameters and Abundancesmentioning

confidence: 90%

Chemical abundances in a high-velocity RR Lyrae star near the bulge

Hansen¹,

Rich

Koch

et al. 2016

A&A

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Low-mass variable high-velocity stars are interesting study cases for many aspects of Galactic structure and evolution. Until recently, the only known high-or hyper-velocity stars were young stars thought to originate from the Galactic center. Wide-area surveys such as APOGEE and BRAVA have found several low-mass stars in the bulge with Galactic rest-frame velocities higher than 350 km s −1 . In this study we present the first abundance analysis of a low-mass RR Lyrae star that is located close to the Galactic bulge, with a space motion of ∼-400 km s −1 . Using medium-resolution spectra, we derived abundances (including upper limits) of 11 elements. These allowed us to chemically tag the star and discuss its origin, although our derived abundances and metallicity, at [Fe/H] = −0.9 dex, do not point toward one unambiguous answer. Based on the chemical tagging, we cannot exclude that it originated in the bulge. However, its retrograde orbit and the derived abundances combined suggest that the star was accelerated from the outskirts of the inner (or even outer) halo during many-body interactions. Other possible origins include the bulge itself, or the star might have been stripped from a stellar cluster or the Sagittarius dwarf galaxy when it merged with the Milky Way.

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Section: Stellar Parameters and Abundancesmentioning

confidence: 90%

Chemical abundances in a high-velocity RR Lyrae star near the bulge

Hansen¹,

Rich

Koch

et al. 2016

A&A

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“…These predictions were compared with the observational data of halo stars from Ryan & Norris (1991) and Schörck et al (2009) (Hamburg/ESO Survey; HES): the model does not agree with the data, as shown in the left panel of Fig. 1.…”

Section: Two-infall + Outflow Modelmentioning

confidence: 99%

Modeling the chemical evolution of the Galaxy halo

Brusadin¹,

Matteuccí

Romano

2013

A&A

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Context. The stellar halo provides precious information about the Galaxy in its early stages of evolution because the most metal-poor (oldest) stars in the Milky Way are found there. Aims. We study the chemical evolution and formation of the Galactic halo through the analysis of its stellar metallicity distribution function and some key elemental abundance patterns. We also test the effects of a possible Population III of zero-metal stars. Methods. Starting from the two-infall model for the Galaxy, which predicts too few low-metallicity stars, we added a gas outflow during the halo phase with a rate proportional to the star formation rate through a free parameter, λ. In addition, we considered a first generation of massive zero-metal stars in this two-infall + outflow model, adopting two different top-heavy initial mass functions and specific Population III yields. Results. The metallicity distribution function of halo stars as predicted from the two-infall + outflow model agrees well with observations when the parameter λ = 14 and the time scale for the first infall, out of which the halo formed, is not longer than 0.2 Gyr, a lower value than suggested previously. Moreover, the abundance patterns [X/Fe] vs. [Fe/H] for C, N, and α-elements O, Mg, Si, S, and Ca agree well with the observational data, as in the case of the two-infall model without outflow. If Population III stars are included, under the assumption of different initial mass functions, the overall agreement of the predicted stellar metallicity distribution function with observational data is poorer than in the case of the two-infall + outflow model without Population III. Conclusions. We conclude that it is fundamental to include both a gas infall and outflow during the halo formation to explain the observed halo metallicity distribution function in the framework of a model assuming that the stars in the inner halo formed mostly in situ. Moreover, we find that there is no satisfactory initial mass function for Population III stars that reproduces the observed halo metallicity distribution function. As a consequence, there is no need for a first generation of only massive stars to explain the evolution of the Galactic halo.

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“…A selection function of B−V = 0.7 was adopted (see Schörck et al 2009, their Table 12). While stars enriched by one SN are hardly affected at all by this bias (i.e., they are mostly found below [Fe/H] = −2.5), the number of stars enriched by more than one SN is significantly smaller, by a factor of ∼7.…”

Section: Stochastic Modelling Of the Chemical Evolution Of Simentioning

confidence: 99%

The Hamburg/ESO R-process Enhanced Star survey (HERES)

Zhang

Karlsson

Christlieb

et al. 2011

A&A

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Aims. To obtain detailed silicon abundances of metal-poor stars, we aim to explore the correlation between the abundance ratios and the stellar parameters and the chemical enrichment of the interstellar medium (ISM). Methods. We determined the silicon abundances of 253 metal-poor stars in the metallicity range −4 < [Fe/H] < −1.5, based on non-local thermodynamic equilibrium (NLTE) line formation calculations of neutral silicon and high-resolution spectra obtained with VLT-UT2/UVES. Results. The T eff dependence of [Si/Fe] noticed in previous investigations is diminished in our abundance analysis owing to the inclusion of NLTE effects. An increasing slope of [Si/Fe] towards decreasing metallicity is present in our results, in agreement with Galactic chemical evolution models. Intrinsic scatter of [Si/Fe] in our sample is small. We identified two dwarfs with [Si/Fe] ∼ +1.0: HE 0131−3953, and HE 1430−1123. These main-sequence turnoff stars are also carbon-enhanced. They may have been pre-enriched by sub-luminous supernovae. Conclusions. The small intrinsic scatter of [Si/Fe] in our sample may imply that these stars formed in a region where the yields of type II supernovae were mixed into a large volume, or that the formation of these stars was strongly clustered, even if the ISM was enriched by single SNa II in a small mixing volume.

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The stellar content of the Hamburg/ESO survey

Cited by 128 publications

References 72 publications

Chemical abundances in a high-velocity RR Lyrae star near the bulge

Chemical abundances in a high-velocity RR Lyrae star near the bulge

Modeling the chemical evolution of the Galaxy halo

The Hamburg/ESO R-process Enhanced Star survey (HERES)

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