J/A+A/593/A28 Halo metal-poor stars chemical data (Fernandez-Alvar+, 2016)
Deep SDSS optical spectroscopy of distant halo stars.
III. Chemical analysis of extremely metal-poor stars.
Fernandez-Alvar E., Allende Prieto C., Beers T.C., Lee Y.S., Masseron T.,
Schneider D.P.
<Astron. Astrophys. 593, A28 (2016)>
=2016A&A...593A..28F 2016A&A...593A..28F (SIMBAD/NED BibCode)
ADC_Keywords: Stars, halo ; Photometry, SDSS ; Abundances
Keywords: stars: abundances - stars: population III - methods: data analysis -
catalogs - Galaxy: halo - stars: carbon
Abstract:
We present the results of an analysis of 107 extremely metal-poor
(EMP) stars with metallicities lower than [Fe/H]=-3.0, identified in
medium-resolution spectra in the Sloan Digital Sky Survey (SDSS). Our
analysis provides estimates of the stellar effective temperatures and
surface gravities, as well as iron, calcium, and magnesium abundances.
We followed the same method as in previous papers of this series. The
method is based on comparisons of the observed spectra with synthetic
spectra. The abundances of Fe, Ca, and Mg were determined by fitting
spectral regions that are dominated by lines of each element. In
addition, we present a technique to determine upper limits for
elements whose features are not detected in a given spectrum. We also
analyzed our sample with the SEGUE stellar parameter pipeline to
obtain additional determinations of the atmospheric parameters and
iron and alpha-element abundances, which we then compare with ours.
In addition, we used these parameters to infer [C/Fe] ratios.
Ca is typically the only element in these spectra with a moderate to
low signal-to-noise ratio and medium resolution in this metallicity
regime with lines that are sufficiently strong to reliably measure its
abundance. Fe and Mg exhibit weaker features that in most cases only
provide upper limits. We measured [Ca/Fe] and [Mg/Fe] for EMP stars in
the SDSS spectra and conclude that most of the stars exhibit the
typical enhancement level for alpha-elements, ~+0.4, although some
stars for which only [Fe/H] upper limits could be estimated indicate
higher [alpha/Fe] ratios. We also find that 26% of the stars in our
sample can be classified as carbon-enhanced metal-poor (CEMP) stars
and that the frequency of CEMP stars also increases with decreasing
metallicity, as has been reported for previous samples. We identify a
rare, bright (g=11.90) EMP star, SDSS J134144.61+474128.6, with
[Fe/H]=-3.27, [C/Fe]=+0.95, and elevated magnesium ([Mg/Fe]=+0.62), an
abundance pattern typical of CEMP-no stars.
Description:
Our stellar spectra come from the SDSS.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table4-6.dat 176 107 SDSS Photometry, radial velocities, stellar
atmospheric parameters and [Fe/H], [Ca/H],
[Mg/H] and [C/Fe]
--------------------------------------------------------------------------------
See also:
J/A+A/403/1105 : Extremely metal-poor giants EW (Francois+, 2003)
J/AJ/128/2402 : Extremely metal-poor star candidates abundances (Lai+, 2004)
J/ApJS/155/651 : Evolution of extremely metal-poor stars (Herwig+, 2004)
J/A+A/490/769 : Yields from extremely metal-poor stars (Campbell+, 2008)
J/A+A/501/519 : Extremely metal-poor turnoff stars abund. (Bonifacio+, 2009)
J/AJ/132/137 : Extremely metal-poor carbon stars abundances (Cohen+, 2006)
J/ApJ/742/54 : CASH project. 14 extremely metal-poor stars (Hollek+, 2011)
J/MNRAS/412/843 : SAGA extremely metal-poor stars (Suda+, 2011)
J/AJ/145/13 : Metal-poor stars from SDSS/SEGUE. Abundances (Aoki+, 2013)
J/ApJ/778/56 : Hamburg/ESO Survey extremely metal-poor stars (Cohen+, 2013)
J/MNRAS/434/1681 : Extremely metal-poor stars CaII triplet (Carrera+, 2013)
J/A+A/568/A7 : Model SDSS colors for halo stars (Allende Prieto+, 2014)
J/A+A/577/A81 : Deep SDSS Optical Spectroscopy. II. (Fernandez-Alvar+, 2015)
Byte-by-byte Description of file: table4-6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- SDSS SDSS Identifier (JHHMMSS.ss+DDMMSS.s)
21- 35 A15 --- PMF SDSS plate-mjd-fiber identifier
37- 45 F9.5 deg RAdeg Right ascension (J2000.0)
47- 55 F9.5 deg DEdeg Declination (J2000.0)
57- 61 F5.2 mag umag SDSS u magnitude
63- 67 F5.2 mag gmag SDSS g magnitude
69- 73 F5.2 mag rmag SDSS r magnitude
75- 79 F5.2 mag imag SDSS i magnitude
81- 85 F5.2 mag zmag SDSS z magnitude
87- 92 F6.1 km/s RV Radial velocity
94- 97 I4 K Teff Effective temperature
99-102 F4.2 [cm/s2] logg Surface gravity
104-108 F5.2 [-] [M/H] Metallicity [M/H]
110-113 F4.2 [-] e_[M/H] rms uncertainty on [M/H]
115-118 I4 K Teffsspp SSPP effective temperature
120-123 F4.2 [cm/s2] loggsspp SSPP surface gravity
125-129 F5.2 [-] [M/H]sspp SSPP metallicity [M/H]
131 A1 --- l_[Fe/H] Limit flag on [Fe/H]
132-136 F5.2 [-] [Fe/H] Metallicity [Fe/H]
138-141 F4.2 [-] e_[Fe/H] ?=- rms uncertainty on [Fe/H]
143-147 F5.2 [-] [Ca/H] Abundance [Ca/H]
149-152 F4.2 [-] e_[Ca/H] rms uncertainty on [Ca/H]
154 A1 --- l_[Mg/H] Limit flag on [Mg/H]
155-159 F5.2 [-] [Mg/H] Abundance [Mg/H]
161-164 F4.2 [-] e_[Mg/H] ?=- rms uncertainty on [Mg/H]
166-170 F5.2 [-] [alpha/Fe]sspp ?=- SSPP abundance [alpha/Fe]
172-176 F5.2 [-] [C/Fe]sspp ?=- SSPP abundance [C/Fe]
--------------------------------------------------------------------------------
Acknowledgements:
Emma Fernandez-Alvar, emma (at)astro.unam.mx
References:
Allende Prieto et al., Paper I 2014A&A...568A...7A 2014A&A...568A...7A, Cat. J/A+A/568/A7
Fernandez-Alvar et al., Paper II 2015A&A...577A..81F 2015A&A...577A..81F, Cat. J/A+A/577/A81
(End) Emma Fernandez-Alvar [UNAM, Mexico], Patricia Vannier [CDS] 22-Jul-2016