Metallicity And Alpha-Element Abundance Measurement In Red Giant Stars From Medium-Resolution Spectra

dc.contributor.utaustinauthorSneden, Christopheren_US
dc.creatorKirby, Evan N.en_US
dc.creatorGuhathakurta, Puragraen_US
dc.creatorSneden, Christopheren_US
dc.date.accessioned2016-04-28T19:35:34Z
dc.date.available2016-04-28T19:35:34Z
dc.date.issued2008-08en
dc.description.abstractWe present a technique that applies spectral synthesis to medium-resolution spectroscopy (MRS; R similar to 6000) in the red (6300 angstrom < lambda < 9100 angstrom) to measure [Fe/H] and [alpha/Fe] of individual red giant stars over a wide metallicity range. We apply our technique to 264 red giant stars in seven Galactic globular clusters and demonstrate that it reproduces the metallicities and alpha-enhancements derived from high-resolution spectroscopy (HRS). The MRS technique excludes the three Ca II triplet lines and instead relies on a plethora of weaker lines. Unlike empirical metallicity estimators, such as the equivalent width of the Ca II triplet, the synthetic method presented here is applicable over an arbitrarily wide metallicity range and is independent of assumptions about the alpha-enhancement. Estimates of cluster mean [Fe/H] from different HRS studies show typical scatter of similar to 0.1 dex but can be larger than 0.2 dex for metal-rich clusters. The scatter in HRS abundance estimates among individual stars in a given cluster is also comparable to 0.1 dex. By comparison, the scatter among MRS [Fe/H] estimates of individual stars in a given cluster is similar to 0.1 dex for most clusters but 0.17 dex for the most metal-rich cluster, M71 (<[Fe/H]> = - 0.8). A star-by-star comparison of HRS versus MRS [alpha/Fe] estimates indicates that the precision in [alpha/Fe](MRS) is 0.05 dex. The errors in [Fe/H](MRS) and [alpha/Fe](MRS) increase beyond 0.25 dex only below signal-to-noise ratios of 20 angstrom(-1), which is typical for existing MRS of the red giant stars in Leo I, one of the most distant Milky Way satellites (250 kpc).en_US
dc.description.departmentAstronomyen_US
dc.description.sponsorshipNSF AST 06-07708, AST 03-07966, AST 06-07852, AST 00-71048en_US
dc.description.sponsorshipNASA/STScI GO-10265.02, GO-10134.02en_US
dc.identifierdoi:10.15781/T2481F
dc.identifier.Filename2008_08_metallicity.pdfen_US
dc.identifier.citationKirby, Evan N., Puragra Guhathakurta, and Christopher Sneden. "Metallicity and alpha-element abundance measurement in red giant stars from medium-resolution spectra." The Astrophysical Journal, Vol. 682, No. 2 (Aug., 2008): 1217.en_US
dc.identifier.doi10.1086/589627en_US
dc.identifier.issn0004-637Xen_US
dc.identifier.urihttp://hdl.handle.net/2152/34841
dc.language.isoEnglishen_US
dc.relation.ispartofen_US
dc.relation.ispartofserialAstrophysical Journalen_US
dc.rightsAdministrative deposit of works to Texas ScholarWorks: This works author(s) is or was a University faculty member, student or staff member; this article is already available through open access or the publisher allows a PDF version of the article to be freely posted online. The library makes the deposit as a matter of fair use (for scholarly, educational, and research purposes), and to preserve the work and further secure public access to the works of the University.en_US
dc.rights.restrictionOpenen_US
dc.subjectglobular clusters : individual (m13, m15, m71, m79 ngc 2419, ngc 7006,en_US
dc.subjectngc 7492)en_US
dc.subjectstars : abundancesen_US
dc.subjectdwarf spheroidal galaxiesen_US
dc.subjectneutral hydrogen collisionsen_US
dc.subjectcluster ngcen_US
dc.subject7006en_US
dc.subjectglobular-clustersen_US
dc.subjectmilky-wayen_US
dc.subjectchemical-compositionen_US
dc.subjectnitrogenen_US
dc.subjectabundancesen_US
dc.subjectoxygen abundancesen_US
dc.subjectstellar contenten_US
dc.subjectgalactic haloen_US
dc.subjectastronomy & astrophysicsen_US
dc.titleMetallicity And Alpha-Element Abundance Measurement In Red Giant Stars From Medium-Resolution Spectraen_US
dc.typeArticleen_US

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