J/A+A/593/A28ivo://CDS.VizieR/J/A+A/593/A28doi:10.26093/cds/vizier.35930028CDSFernandez-Alvar E.Allende Prieto C.Beers T.C.Lee Y.S.Masseron T.,Schneider D.P.2018-07-02T14:50:26Z2016-09-01T09:01:38ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frhalo-starsvisible-astronomysloan-photometrychemical-abundancesWe 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.2016A&A...593A..28Fhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/593/A28CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/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)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/593/A28https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/593/A28http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/593/A28https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/593/A28https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/593/A28http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/593/A28GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/593/A28/table4-6 (SDSS Photometry, radial velocities, stellar atmospheric parameters and [Fe/H], [Ca/H], [Mg/H] and [C/Fe])https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/593/A28/table4-6?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/593/A28/table4-6?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/593/A28/table4-6?GETtext/xml+votable180.050000true167.1161461.571990.0055555555555555566/0 2 22 31 402 723 909 2067 2097 2171 4110-4111 4179 4186 4421 4628 4639 4699 4931 4956 5217 5350 5525 5589 5733 5810 5896 5973 6126 6591 6652 7294 7385 7527 7757 8260 8342 8518 8670 8819 8821 8992-8993 9126 9287 9297-9298 9341 9583 10147 10238 10442 10828 10915 11029 11072 12523 14021 16293 17232 17406 17758 17767 17838 18011 18019 18608 19171 19270 19540 19691 19917 20163 22341 22826 23207 23471 24046 24125 25948 25985 26021 26050 26205 26539 26982 27257 27846 27875 27939 28009 28269 28299 28344 28521 28666 30041 31445 31447 31908 32519 32557 36779-36780 368172.040811542443644e-19 6.090060298487514e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/593/A28?format=asciiOpticaldefaultJ/A+A/593/A28/table4-6SDSS Photometry, radial velocities, stellar atmospheric parameters and [Fe/H], [Ca/H], [Mg/H] and [C/Fe]SimbadNameSimbad column added by the CDSmeta.idchargmagSDSS g magnitudemagphot.mag;em.opt.BfloatrmagSDSS r magnitudemagphot.mag;em.opt.RfloatrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSDSSSDSS Identifier (JHHMMSS.ss+DDMMSS.s)meta.id;meta.maincharPMFSDSS plate-mjd-fiber identifiermeta.idcharRAJ2000Right ascension (J2000.0)degpos.eq.ra;meta.mainDEJ2000Declination (J2000.0)degpos.eq.dec;meta.mainumagSDSS u magnitudemagphot.mag;em.opt.UfloatimagSDSS i magnitudemagphot.mag;em.opt.IfloatzmagSDSS z magnitudemagphot.mag;em.opt.IfloatRVRadial velocitykm/sphys.veloc;pos.heliocentricfloatTeffEffective temperatureKphys.temperature.effectiveintloggSurface gravitylog(cm.s**-2)phys.gravityfloat[M/H]Metallicity [M/H]phys.abund.Zfloate_[M/H]rms uncertainty on [M/H]stat.error;phys.abundfloatTeffssppSSPP effective temperatureKphys.temperature.effectiveintloggssppSSPP surface gravitylog(cm.s**-2)phys.gravityfloat[M/H]ssppSSPP metallicity [M/H]phys.abund.Zfloatl_[Fe/H]Limit flag on [Fe/H]meta.code.error;phys.abund.Fechar[Fe/H]Metallicity [Fe/H]phys.abund.Zfloate_[Fe/H]? rms uncertainty on [Fe/H]stat.error;phys.abund.Fefloatnullable[Ca/H]Abundance [Ca/H]phys.abundfloate_[Ca/H]rms uncertainty on [Ca/H]stat.error;phys.abundfloatl_[Mg/H]Limit flag on [Mg/H]meta.code.error;phys.abundchar[Mg/H]Abundance [Mg/H]phys.abundfloate_[Mg/H]? rms uncertainty on [Mg/H]stat.error;phys.abundfloatnullable[alpha/Fe]sspp? SSPP abundance [alpha/Fe]phys.abundfloatnullable[C/Fe]sspp? SSPP abundance [C/Fe]phys.abundfloatnullableSpInteractive spectrum from SDSSmeta.ref.urlchar