%0 Journal Article
%T Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. I. Carbon Abundance Estimation and Frequency of CEMP Stars
%+ Laboratoire Univers et Particules de Montpellier (LUPM)
%A Lee, Young Sun
%A Beers, Timothy C.
%A Masseron, Thomas
%A Plez, Bertrand
%A Rockosi, Constance M.
%A Sobeck, Jennifer
%A Yanny, Brian
%A Lucatello, Sara
%A Sivarani, Thirupathi
%A Placco, Vinicius M.
%A Carollo, Daniela
%Z 19 pages, 10 figures, 6 tables, accepted for publication in AJ on August 20, 2013
%< avec comité de lecture
%Z LUPM:13-034
%@ 0004-6256
%J The Astronomical Journal
%I American Astronomical Society
%V 146
%P 132
%8 2013-10-18
%D 2013
%Z 1310.3276
%R 10.1088/0004-6256/146/5/132
%Z Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR]
%Z Physics [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR]Journal articles
%X We describe a method for the determination of stellar [C/Fe] abundance ratios using low-resolution (R = 2000) stellar spectra from the SDSS and SEGUE. By means of a star-by-star comparison with a set of SDSS/SEGUE spectra with available estimates of [C/Fe] based on published high-resolution analyses, we demonstrate that we can measure [C/Fe] from SDSS/SEGUE spectra with S/N > 15 to a precision better than 0.35 dex. Using the measured carbon-to-iron abundance ratios obtained by this technique, we derive the frequency of carbon-enhanced stars ([C/Fe] > +0.7) as a function of [Fe/H], for both the SDSS/SEGUE stars and other samples from the literature. We find that the differential frequency slowly rises from almost zero to about 14% at [Fe/H] ~ -2.4, followed by a sudden increase, by about a factor of three, to 39% from [Fe/H] ~ -2.4 to [Fe/H] ~ -3.7. We also examine how the cumulative frequency of CEMP stars varies across different luminosity classes. The giant sample exhibits a cumulative CEMP frequency of 32% for [Fe/H] < -2.5, 31% for [Fe/H] < -3.0, and 33% for [Fe/H] < -3.5. For the main-sequence turnoff stars, we obtain a lower cumulative CEMP frequency, around 10% for [Fe/H] < -2.5. The dwarf population displays a large change in the cumulative frequency for CEMP stars below [Fe/H] = -2.5, jumping from 15% for [Fe/H] < -2.5 to about 75% for [Fe/H] < -3.0. When we impose a restriction with respect to distance from the Galactic mid-plane (|Z| < 5 kpc), the frequency of the CEMP giants does not increase at low metallicity ([Fe/H] < -2.5), but rather, decreases, due to the dilution of C-rich material in stars that have undergone mixing with CNO-processed material from their interiors. The frequency of CEMP stars near the main-sequence turnoff, which are not expected to have experienced mixing, increases for [Fe/H] < -3.0. [abridged]
%G English
%L hal-00873594
%U https://hal.science/hal-00873594
%~ IN2P3
%~ CNRS
%~ UNIV-MONTP2
%~ LUPM
%~ MIPS
%~ UNIV-MONTPELLIER
%~ LUPM_AS
%~ UM1-UM2