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Deep SDSS optical spectroscopy of distant halo stars I. Atmospheric parameters and stellar metallicity distribution

Allende Prieto, C.; Fernandez-Alvar, E.; Schlesinger, K. J.; Lee, Y. S.; Morrison, H. L.; Schneider, D. P.; Beers, T. C.; Bizyaev, D.; Ebelke, G. and Malanushenko, E., et al. (2014) In Astronomy & Astrophysics 568.
Abstract
Aims. We analyze a sample of tens of thousands of spectra of halo turnoff stars, obtained with the optical spectrographs of the Sloan Digital Sky Survey (SDSS), to characterize the stellar halo population "in situ" out to a distance of a few tens of kpc from the Sun. In this paper we describe the derivation of atmospheric parameters. We also derive the overall stellar metallicity distribution based on F-type stars observed as flux calibrators for the Baryonic Oscillations Spectroscopic Survey (ROSS). Methods. Our analysis is based on an automated method that determines the set of parameters of a model atmosphere that reproduces each obserxrci spectrum best. We used an optimization algorithm and evaluate model fluxes by means of... (More)
Aims. We analyze a sample of tens of thousands of spectra of halo turnoff stars, obtained with the optical spectrographs of the Sloan Digital Sky Survey (SDSS), to characterize the stellar halo population "in situ" out to a distance of a few tens of kpc from the Sun. In this paper we describe the derivation of atmospheric parameters. We also derive the overall stellar metallicity distribution based on F-type stars observed as flux calibrators for the Baryonic Oscillations Spectroscopic Survey (ROSS). Methods. Our analysis is based on an automated method that determines the set of parameters of a model atmosphere that reproduces each obserxrci spectrum best. We used an optimization algorithm and evaluate model fluxes by means of inter-polation in a precomputed grid, In our analysis, we account for the spectrograph's varying resolution as a function of fiber and wavelength. Our results for early SDSS (pre-BOSS upgrade) data compare well with those from the SEGUE Stellar Parameter Pipeline (SSPP). except for stars with log g (cgs units) lower than 2.5. Results. An analysis of stars in the globular cluster M 13 reveals a dependence of the inferred metallicity on surface gravity for stars with log g < 2.5, confirming the systematics identified in the comparison with the SSPP. We find that our rnetallicity estimates are, significantly more precise than the SSPP results. We also find excellent agreement with several independent analyses. We show that the SDSS color criteria for selecting F-type halo turnoff stars as flux calibrators efficiently excludes stars with high metallieities, but does not significantly distort the shape of the metallicity distribution at low rnetallicity. We obtain a halo metathcity distribution that is narrower and more asymmetric than in previous studies. The lowest gravity stars in our sample at tens of kpc from the Sun, indicate a shift of the metallicity distribution to lower abundances, consistent with what is expected from a dual halo system in the Milky Way. (Less)
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methods: observational, techniques: spectroscopic, stars: atmospheres, stars: fundamental parameters, stars: Population H, Galaxy: halo
in
Astronomy & Astrophysics
volume
568
publisher
EDP Sciences
external identifiers
  • wos:000341185900103
  • scopus:84905506599
ISSN
0004-6361
DOI
10.1051/0004-6361/201424053
language
English
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yes
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a0e305ba-f2a4-44da-bcf3-d49b497196b1 (old id 4706728)
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2014-10-23 11:25:36
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@article{a0e305ba-f2a4-44da-bcf3-d49b497196b1,
  abstract     = {Aims. We analyze a sample of tens of thousands of spectra of halo turnoff stars, obtained with the optical spectrographs of the Sloan Digital Sky Survey (SDSS), to characterize the stellar halo population "in situ" out to a distance of a few tens of kpc from the Sun. In this paper we describe the derivation of atmospheric parameters. We also derive the overall stellar metallicity distribution based on F-type stars observed as flux calibrators for the Baryonic Oscillations Spectroscopic Survey (ROSS). Methods. Our analysis is based on an automated method that determines the set of parameters of a model atmosphere that reproduces each obserxrci spectrum best. We used an optimization algorithm and evaluate model fluxes by means of inter-polation in a precomputed grid, In our analysis, we account for the spectrograph's varying resolution as a function of fiber and wavelength. Our results for early SDSS (pre-BOSS upgrade) data compare well with those from the SEGUE Stellar Parameter Pipeline (SSPP). except for stars with log g (cgs units) lower than 2.5. Results. An analysis of stars in the globular cluster M 13 reveals a dependence of the inferred metallicity on surface gravity for stars with log g &lt; 2.5, confirming the systematics identified in the comparison with the SSPP. We find that our rnetallicity estimates are, significantly more precise than the SSPP results. We also find excellent agreement with several independent analyses. We show that the SDSS color criteria for selecting F-type halo turnoff stars as flux calibrators efficiently excludes stars with high metallieities, but does not significantly distort the shape of the metallicity distribution at low rnetallicity. We obtain a halo metathcity distribution that is narrower and more asymmetric than in previous studies. The lowest gravity stars in our sample at tens of kpc from the Sun, indicate a shift of the metallicity distribution to lower abundances, consistent with what is expected from a dual halo system in the Milky Way.},
  articleno    = {A7},
  author       = {Allende Prieto, C. and Fernandez-Alvar, E. and Schlesinger, K. J. and Lee, Y. S. and Morrison, H. L. and Schneider, D. P. and Beers, T. C. and Bizyaev, D. and Ebelke, G. and Malanushenko, E. and Malanushenko, V. and Oravetz, D. and Pan, K. and Simmons, A. and Simmerer, Jennifer and Sobeck, J. and Robin, A. C.},
  issn         = {0004-6361},
  keyword      = {methods: observational,techniques: spectroscopic,stars: atmospheres,stars: fundamental parameters,stars: Population H,Galaxy: halo},
  language     = {eng},
  publisher    = {EDP Sciences},
  series       = {Astronomy & Astrophysics},
  title        = {Deep SDSS optical spectroscopy of distant halo stars I. Atmospheric parameters and stellar metallicity distribution},
  url          = {http://dx.doi.org/10.1051/0004-6361/201424053},
  volume       = {568},
  year         = {2014},
}