Statistical methods of automatic spectral classification and their application to the Hamburg/ESO Survey

Christlieb, N.; Wisotzki, L.; Graßhoff, Gerd

doi:10.1051/0004-6361:20020830

Cited by 41 publications

(34 citation statements)

References 22 publications

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“…More recently, cosmological surveys of galaxies and quasars, including observations of stars for different purposes, have taken the lead in explorFull Table 1 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/568/A7 ing the most distant parts of the halo. The stars with the lowest known iron abundance come from candidates identified in the Hamburg-ESO survey (Wisotzki et al 1996;Christlieb et al 1999Christlieb et al , 2002 or the Sloan Digital Sky Survey (SDSS; York et al 2000;Bonifacio et al 2012), and these studies constitute the best available database for studying the main properties of the stellar Galactic halo.…”

Section: Introductionmentioning

confidence: 99%

Deep SDSS optical spectroscopy of distant halo stars

Prieto

Fernández-Alvar

Schlesinger

et al. 2014

A&A

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Aims. 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). Methods. Our analysis is based on an automated method that determines the set of parameters of a model atmosphere that reproduces each observed spectrum best. We used an optimization algorithm and evaluate model fluxes by means of interpolation in a precomputed 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 with log g (cgs units) lower than 2.5.Results. An analysis of stars in the globular cluster M 13 reveals a dependence of the inferred metallicity on surface gravity for stars with log g < 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 what is expected from a dual halo system in the Milky Way.

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Section: Introductionmentioning

confidence: 99%

Deep SDSS optical spectroscopy of distant halo stars

Prieto

Fernández-Alvar

Schlesinger

et al. 2014

A&A

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“…Low-metallicity stellar surveys.-Searches for metal-poor stars have been pursued by spectroscopy of high proper motion samples (Carney et al 1994;Ryan & Norris 1991) and highlatitude objective-prism surveys ( BPS92; Christlieb et al 2002). The bulk of verified metal-poor stars are dwarfs near the turnoff because of the small volumes of space included in proper-motion searches on the one hand and the temperature/abundance degeneracy that plagues objective-prism searches for metal-poor red giants (Preston 2000) on the other.…”

Section: Introductionmentioning

confidence: 99%

Atmospheres, Chemical Compositions, and Evolutionary Histories of Very Metal-Poor Red Horizontal-Branch Stars in the Galactic Field and in NGC 7078 (M15)

Preston¹,

Sneden²,

Thompson³

et al. 2006

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We have conducted spectrum analyses of 24 field metal-poor (½Fe/H < À2) red horizontal-branch ( RHB) stars identified in the HK objective-prism survey and 6 such stars in the globular cluster M15, based on high-quality spectra (R $ 40;000, S/N $ 100) obtained with the Magellan Inamori Kyocera Echelle spectrograph at the Clay 6.5 m telescope at Las Campanas Observatory. The atmospheric parameters of the RHB stars provide interesting bridges between turnoff stars of similar temperature and red giant branch (RGB) stars of similar gravity, and they permit investigations of abundance trends [X/Fe] versus [Fe/H] in a relatively unexplored region of the temperature-gravity plane. We find that the T eff , log g, v t , and [Fe/H] values determined from our spectra are consistent with expectations from literature spectroscopic studies of other evolved metal-poor stellar classes. We show that the RHB stars have abundance distributions that are consistent with typical halo stars of similar metallicities. The photometric and spectroscopic gravities of the M15 stars differ by amounts that grow with declining temperature. We use a regression derived from these differences to calculate photometric gravities for the field RHB stars. Then we use the locations of the field RHB stars among the evolutionary tracks of Cassisi et al. in the log g versus log T eA plane to estimate their masses and lifetimes as RHB stars. We use these lifetimes to estimate the size of the metal-poor HB population from which they arise. Then, using counts of HB and RGB stars in metal-poor globular clusters, we conclude that the number of metalpoor RGB stars at high latitudes (jbj > 30 ) brighter than V ¼ 15 exceeds those identified in extant objective-prism surveys by more than an order of magnitude. Finally, we deduce the effective temperature of the fundamental red edge of the metal-poor RR Lyrae instability strip, log T eA (FRE) ¼ 3:80 AE 0:01, from the interface between the temperature distributions of metal-poor field RHB stars and the RR Lyrae stars of similar [Fe/H] in five metal-poor globular clusters.

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“…Another 1275 deg 2 covered by the HES is now being scanned and analyzed for candidates. The selection of metal-poor candidates from the HES database of digital objective-prism spectra is performed using quantitative criteria including automatic spectral classification (Christlieb, Wisotzki, & Grasshoff 2002). The strength of the CaII K line is determined using the KP line index , as measured directly from the objective-prism spectra.…”

Section: The Hk Survey and The Hamburg/eso Surveymentioning

confidence: 99%

The Metallicity Distribution Function of the Halo of the Milky Way

et al. 2005

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We report on the distribution of metallicities, [Fe/H], for very metal-poor stars in the halo of the Galaxy. Although the primary information on the nature of the Metallicity Distribution Function (MDF) is obtained from the two major recent surveys for metal-poor stars, the HK survey of Beers and collaborators, and the Hamburg/ESO Survey of Christlieb and collaborators, we also discuss the MDF derived from the publicly available database of stellar spectra and photometry contained in the third data release of the Sloan Digital Sky Survey (SDSS DR-3). Even though the SDSS was not originally planned as a stellar survey, significant numbers of stars have been observed to date -- DR-3 contains spectroscopy for over 70,000 stars, at least half of which are suitable for abundance determinations. There are as many very metal-poor ([Fe/H] < -2.0) stars in DR-3 as have been obtained from all previous survey efforts combined. We also discuss prospects for significant expansion of the list of metal-poor stars to be obtained from the recently funded extension of the SDSS, which includes the project SEGUE: Sloan Extension for Galactic Understanding and Exploration.Comment: To appear in: From Lithium to Uranium: Elemental Tracers of Early Cosmic Evolution, IAU Symposium 228, V. Hill, P. Francois & F. Primas, ed

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Statistical methods of automatic spectral classification and their application to the Hamburg/ESO Survey

Cited by 41 publications

References 22 publications

Deep SDSS optical spectroscopy of distant halo stars

Deep SDSS optical spectroscopy of distant halo stars

Atmospheres, Chemical Compositions, and Evolutionary Histories of Very Metal-Poor Red Horizontal-Branch Stars in the Galactic Field and in NGC 7078 (M15)

The Metallicity Distribution Function of the Halo of the Milky Way

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