J/A+A/577/A81 Deep SDSS Optical Spectroscopy. II. (Fernandez-Alvar+, 2015)
Deep SDSS Optical Spectroscopy of Distant Halo Stars.
II. Iron, calcium, and magnesium abundances.
Fernandez-Alvar E., Allende Prieto C., Schlesinger K.J., Beers T.C.,
Robin A.C., Schneider D.P., Lee Y.S., Bizyaev D., Ebelke G.,
Malanushenko E., Malanushenko V., Oravetz D., Pan K., Simmons A.
<Astron. Astrophys. 577, A81 (2015)>
=2015A&A...577A..81F 2015A&A...577A..81F
ADC_Keywords: Stars, halo ; Stars, fundamental ; Stars, distances ;
Abundances, [Fe/H]
Keywords: Galaxy: halo - Galaxy: abundances - Galaxy: structure
Abstract:
We analyze a sample of 3942 low-resolution (R∼2000) optical spectra
from the Sloan Digital Sky Survey (SDSS), focusing on stars with
effective temperatures 5800<Teff<6300K, and distances from the Milky
Way plane in excess of 5kpc, and determine their abundances of Fe, Ca,
and Mg. This work follows the same methodology as in the previous
paper in this series, deriving atmospheric parameters by chi2
minimization, but we now obtain the abundances of individual elements
by fitting their associated spectral lines. Distances are calculated
from absolute magnitudes obtained by a statistical comparison of our
stellar parameters with stellar-evolution models. The observations
reveal a decrease in the abundances of iron, calcium and magnesium at
large distances from the Galactic center. The median abundances for
the halo stars analyzed are fairly constant up to a Galactocentric
distance r∼20kpc, rapidly decrease between r∼20 and r∼40kpc, and
flatten out to significantly lower values at larger distances,
consistent with previous studies. In addition, we examine the Ca/Fe
and Mg/Fe ratios as a function of Fe/H and Galactocentric distance.
Our results show that the most distant parts of the halo show a
steeper variation of the Ca/Fe and Mg/Fe with iron. We found that at
the range -1.6<[Fe/H]←0.4 the Ca/Fe ratio decreases with distance, in
agreement with earlier results based on local stars. However, the
opposite trend is apparent for Mg/Fe. Our conclusion that the outer
regions of the halo are more metal-poor than the inner regions, based
on in-situ observations of distant stars, is in concert with recent
results based on inferences from the kinematics of more local stars,
and with predictions of recent galaxy formation simulations for
galaxies similar to the Milky Way.
Description:
The tables include the stellar parameters, chemical abundances
([Fe/H], [Ca/H] and [Mg/H]) and distance estimates (from the Sun, the
center of the Galaxy and the Galactic plane) for our analyzed samples
of halo stars.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 112 2835 *Stellar parameters, abundances and distances for
SDSS/SEGUE halo sample
table3.dat 112 1109 *Stellar parameters, abundances and distances for
BOSS halo sample
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Note on table2.dat and table3.dat: The analyzed SDSS files were obtained
from http://data.sdss3.org/sas/dr12.
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See also:
J/A+A/568/A7 : Model SDSS colors for halo stars (Allende Prieto+, 2014)
Byte-by-byte Description of file: table2.dat table3.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- PMF Plate-mjd-fiber identification
17- 21 F5.2 rad b Galactic latitude
23- 26 F4.2 rad l Galactic longitude
28- 31 I4 K Teff [5800/6300] Effective temperature
33- 35 I3 K e_Teff [8/122] Effective temperature error
37- 41 F5.2 [cm/s2] logg [2.5/4.4] log10 of the surface gravity
43- 47 F5.2 [cm/s2] e_logg [0.05/1] log10 of the surface gravity error
49- 53 F5.2 [Sun] [Fe/H] i[-3.7/0.5] Iron abundance
55- 58 F4.2 [Sun] e_[Fe/H] [0.05/0.5] Iron abundance error
60- 65 F6.2 [Sun] [Ca/H] [-4.3/-0.2]?=-99 Calcium abundance
67- 72 F6.2 [Sun] e_[Ca/H] [0.01/0.4]?=-99 Calcium abundance error
74- 79 F6.2 [Sun] [Mg/H] [-3.6/-0]?=-99 Magnesium abundance
81- 86 F6.2 [Sun] e_[Mg/H] [0.04/0.5]?=-99 Magnesium abundance error
88- 93 F6.2 kpc dsun [5/127] Distance from the sun
95- 98 F4.2 kpc e_dsun [0.2/1.5] Distance from the sun error
100-105 F6.2 kpc r [5.7/132] Distance from the Galaxy center
107-112 F6.2 kpc Z [-76./103] Distance from the galactic plane
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Acknowledgements:
Emma Fernandez-Alvar, emmafa_ext(at)iac.es
History:
Allende Prieto et al., Paper I 2014A&A...568A...7A 2014A&A...568A...7A, Cat. J/A+A/568/A7
(End) Patricia Vannier [CDS] 24-Feb-2015