Bibcode
Allende Prieto, C.; Fernández-Alvar, E.; Schlesinger, K. J.; Lee, Y. S.; Morrison, H. L.; Schneider, D. P.; Beers, T. C.; Bizyaev, D.; Ebelke, G.; Malanushenko, E.; Malanushenko, V.; Oravetz, D.; Pan, K.; Simmons, A.; Simmerer, J.; Sobeck, J.; Robin, A. C.
Bibliographical reference
Astronomy and Astrophysics, Volume 568, id.A7, 9 pp.
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8
2014
Journal
Citations
65
Refereed citations
61
Description
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 (BOSS). Methods: Our analysis is based on an
automated method that determines the set of parameters of a model
atmosphere that reproduces each observed spectrum best. We used an
optimization algorithm and evaluate model fluxes by means of
interpolation 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 metallicity 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
metallicities, but does not significantly distort the shape of the
metallicity distribution at low metallicity. We obtain a halo
metallicity 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.
Full Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/568/A7
Related projects
Chemical Abundances in Stars
Stellar spectroscopy allows us to determine the properties and chemical compositions of stars. From this information for stars of different ages in the Milky Way, it is possible to reconstruct the chemical evolution of the Galaxy, as well as the origin of the elements heavier than boron, created mainly in stellar interiors. It is also possible to
Carlos
Allende Prieto