J/A+A/568/A7 Model SDSS colors for halo stars (Allende Prieto+, 2014)
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.,
Malanushenko E., Oravetz D., Pan K., Simmons A., Simmerer J., Sobeck J.,
Robin A.C.
<Astron. Astrophys. 568, A7 (2014)>
=2014A&A...568A...7A 2014A&A...568A...7A
ADC_Keywords: Models, atmosphere ; Photometry, SDSS ; Effective temperatures ;
Abundances, [Fe/H]; Stars, F-type ; Stars, metal-deficient
Keywords: methods: observational - techniques: spectroscopic -
stars: abundances - stars: fundamental parameters -
stars: population II - Galaxy: halo
Abstract:
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). Our analysis is based on an automated
method that determines the set of parameters of a model atmosphere
that best reproduces each observed spectrum. We use an optimization
algorithm and evaluate model fluxes by means of interpolation in a
pre-computed 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 at
logg (cgs units) lower than 2.5.
An analysis of stars in the globular cluster M13 reveals a dependence
of the inferred metallicity on surface gravity for stars with
logg<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 that expected from a dual halo system in the Milky Way.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 54 3808 Model SDSS ugriz colors for Kurucz model atmospheres
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 F6.2 --- [Fe/H] [-4/0.5] Metallicity
8- 15 I8 K Teff [3500/50000] Effective temperature
17- 22 F6.2 [cm/s2] logg [0/5] log10 of the surface gravity
24- 30 F7.3 mag u-g Model SDSS u-g color index
32- 38 F7.3 mag g-r Model SDSS g-r color index
40- 46 F7.3 mag r-i Model SDSS r-i color index
48- 54 F7.3 mag i-z Model SDSS i-z color index
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Acknowledgements:
Carlos Allende Prieto, callende (at)iac.es
(End) Patricia Vannier [CDS] 18-Jun-2014