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Searches for Metal-Poor Stars from the Hamburg/ESO Survey using the CH G-band | | Vinicius M. Placco
; Catherine R. Kennedy
; Timothy C. Beers
; Norbert Christlieb
; Silvia Rossi
; Thirupathi Sivarani
; Young Sun Lee
; Dieter Reimers
; Lutz Wisotzki
; | | Date: |
19 Sep 2011 | | Abstract: | We describe a new method to search for metal-poor candidates from the
Hamburg/ESO objective-prism survey (HES) based on identifying stars with
apparently strong CH G-band strengths for their colors. The hypothesis we
exploit is that large over-abundances of carbon are common among metal-poor
stars. The selection was made by considering two line indices in the 4300A
region, applied directly to the low-resolution prism spectra. This work also
extends a previously published method by adding bright sources to the sample.
The spectra of these stars suffer from saturation effects, compromising the
index calculations and leading to an undersampling of the brighter candidates.
Visual inspection and classification of the spectra from the HES plates yielded
a list of 5,288 new metal-poor candidates, which are presently being used as
targets for medium-resolution spectroscopic follow-up. Estimates of the stellar
atmospheric parameters, as well as carbon abundances, are now available for 117
of the first candidates, based on follow-up medium-resolution spectra obtained
with the SOAR 4.1m and Gemini 8m telescopes. We demonstrate that our new method
improves the metal-poor star fractions found by our pilot study by up to a
factor of three in the same magnitude range, as compared with our pilot study
based on only one CH G-band index. Our selection scheme obtained roughly a 40%
success rate for identification of stars with [Fe/H] < -1.0; the primary
contaminant is late-type stars with near solar abundances and, often, emission
line cores that filled in the CaII K line on the prism spectrum. Because the
selection is based on carbon, we greatly increase the numbers of known CEMP
stars from the HES with intermediate metallicities -2.0 < [Fe/H] < -1.0, which
previous survey efforts undersampled. There are eight newly discovered stars
with [Fe/H] < -3.0 in our sample, including two with [Fe/H] < -3.5. | | Source: | arXiv, 1109.3993 | | Services: | Forum | Review | PDF | Favorites | |
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