The stellar content of the Hamburg/ESO survey IV. Selection of candidate metal-poor stars

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Erscheinungsjahr:
2008
Medientyp:
Text
Schlagworte:
  • Galaxy: evolution
  • Galaxy: formation
  • Galaxy: halo
  • Galaxy: stellar content
  • Stars: population II
  • Surveys
Beschreibung:
  • We present the quantitative methods used for selecting candidate metal-poor stars in the Hamburg/ESO objective-prism survey (HES). The selection is based on the strength of the Ca II K line, colors (both measured directly from the digital HES spectra), as well as colors from the 2 Micron All Sky Survey. The KP index for Ca II K can be measured from the HES spectra with an accuracy of 1.0 Å, and a calibration of the HES colors, using CCD photometry, yields a 1-σuncertainty of 0.07 mag for stars in the color range . These accuracies make it possible to reliably reject stars with [Fe/H] > -2.0 without sacrificing completeness at the lowest metallicities. A test of the selection using 1121 stars of the HK survey of Beers, Preston, and Shectman present on HES plates suggests that the completeness at [Fe/H] < -3.5 is close to 100% and that, at the same time, the contamination of the candidate sample with false positives is low: 50% of all stars with [Fe/H] > -2.5 and 97% of all stars with [Fe/H] > -2.0 are rejected. The selection was applied to 379 HES fields, covering a nominal area of 8853 deg2 of the southern high Galactic latitude sky. The candidate sample consists of 20 271 stars in the magnitude range 10 18. A comparison of the magnitude distribution with that of the HK survey shows that the magnitude limit of the HES sample is about 2 mag fainter. Taking the overlap of the sky areas covered by both surveys into account, it follows that the survey volume for metal-poor stars has been increased by the HES by about a factor of 10 with respect to the HK survey. We have already identified several very rare objects with the HES, including, e.g., the three most heavy-element deficient stars currently known. © 2008 ESO.
Lizenz:
  • info:eu-repo/semantics/openAccess
Quellsystem:
Forschungsinformationssystem der UHH
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oai:www.edit.fis.uni-hamburg.de:publications/4e5b3e13-631d-4d79-a96b-dab3d80671ca