Browsing by Subject "survey heres"
Now showing 1 - 2 of 2
- Results Per Page
- Sort Options
Item The Chemical Abundances Of Stars In The Halo (CASH) Project. II. A Sample Of 14 Extremely Metal-Poor Stars(2011-11) Hollek, Julie K.; Frebel, Anna; Roederer, Ian U.; Sneden, Christopher; Shetrone, Matthew; Beers, Timothy C.; Kang, Sung-Ju; Thom, Christopher; Hollek, Julie K.; Sneden, Christopher; Shetrone, MatthewWe present a comprehensive abundance analysis of 20 elements for 16 new low-metallicity stars from the Chemical Abundances of Stars in the Halo (CASH) project. The abundances have been derived from both Hobby-Eberly Telescope High Resolution Spectrograph snapshot spectra (R similar to 15,000) and corresponding high-resolution (R similar to 35,000) Magellan Inamori Kyocera Echelle spectra. The stars span a metallicity range from [Fe/H] from -2.9 to -3.9, including four new stars with [Fe/H] < -3.7. We find four stars to be carbon-enhanced metal-poor (CEMP) stars, confirming the trend of increasing [C/Fe] abundance ratios with decreasing metallicity. Two of these objects can be classified as CEMP-no stars, adding to the growing number of these objects at [Fe/H]< -3. We also find four neutron-capture-enhanced stars in the sample, one of which has [Eu/Fe] of 0.8 with clear r-process signatures. These pilot sample stars are the most metal-poor ([Fe/H] less than or similar to -3.0) of the brightest stars included in CASH and are used to calibrate a newly developed, automated stellar parameter and abundance determination pipeline. This code will be used for the entire similar to 500 star CASH snapshot sample. We find that the pipeline results are statistically identical for snapshot spectra when compared to a traditional, manual analysis from a high-resolution spectrum.Item The Stellar Content Of The Hamburg/ESO Survey - IV. Selection Of Candidate Metal-Poor Stars(2008-06) Christlieb, N.; Schorck, T.; Frebel, A.; Beers, T. C.; Wisotzki, L.; Reimers, D.; Frebel, A.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, B - V colors (both measured directly from the digital HES spectra), as well as J - K 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 angstrom, and a calibration of the HES B - V colors, using CCD photometry, yields a 1-sigma uncertainty of 0.07 mag for stars in the color range 0.3 < B - V < 1.4. 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 deg(2) of the southern high Galactic latitude sky. The candidate sample consists of 20 271 stars in the magnitude range 10 less than or similar to B less than or similar to 18. A comparison of the magnitude distribution with that of the HK survey shows that the magnitude limit of the HES sample is about 2mag 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.