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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

CARBON-ENHANCED METAL-POOR STARS IN SDSS/SEGUE. I. CARBON ABUNDANCE ESTIMATION AND FREQUENCY OF CEMP STARS

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Author(s):
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Lee, Young Sun [1] ; Beers, Timothy C. [2, 3] ; Masseron, Thomas [4] ; Plez, Bertrand [5] ; Rockosi, Constance M. [6] ; Sobeck, Jennifer [7, 8, 9] ; Yanny, Brian [10] ; Lucatello, Sara [11] ; Sivarani, Thirupathi [12] ; Placco, Vinicius M. [2, 13] ; Carollo, Daniela [14]
Total Authors: 11
Affiliation:
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[1] New Mexico State Univ, Dept Astron, Las Cruces, NM 88003 - USA
[2] Natl Opt Astron Observ, Tucson, AZ 85719 - USA
[3] Michigan State Univ, JINA, E Lansing, MI 48824 - USA
[4] Univ Libre Brussels, Inst Astron & Astrophys, B-1050 Brussels - Belgium
[5] Univ Montpellier 2, CNRS, Lab Univers & Particules Montpellier, F-34095 Montpellier - France
[6] Univ Calif Santa Cruz, Dept Astron & Astrophys, UCO Lick Observ, Santa Cruz, CA 95064 - USA
[7] Univ Chicago, Dept Astron & Astrophys, Chicago, IL 60637 - USA
[8] Univ Nice Sophia Antipolis, CNRS, Observ Cote Azur, Lab Lagrange, UMR7293, F-06304 Nice 04 - France
[9] Univ Chicago, JINA, Chicago, IL 60637 - USA
[10] Fermilab Natl Accelerator Lab, Batavia, IL 60510 - USA
[11] Osserv Astron Padova, INAF, I-35122 Padua - Italy
[12] Indian Inst Astrophys, Bangalore 560034, Karnataka - India
[13] Univ Sao Paulo, Dept Astron, Inst Astron Geofis & Ciencias Atmosfer, BR-05508090 Sao Paulo - Brazil
[14] Macquarie Univ, Dept Phys & Astron, Astron Astrophys & Astrophoton Res Ctr, N Ryde, NSW 2019 - Australia
Total Affiliations: 14
Document type: Journal article
Source: ASTRONOMICAL JOURNAL; v. 146, n. 5 NOV 2013.
Web of Science Citations: 75
Abstract

We describe a method for the determination of stellar {[}C/Fe] abundance ratios using low-resolution (R = 2000) stellar spectra from the Sloan Digital Sky Survey (SDSS) and its Galactic sub-survey, the Sloan Extension for Galactic Understanding and Exploration (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 angstrom(-1) to a precision better than 0.35 dex for stars with atmospheric parameters in the range T-eff = {[}4400, 6700] K, log g = {[}1.0, 5.0], {[}Fe/H] = {[}-4.0, +0.5], and {[}C/Fe] = {[}-0.25, +3.5]. 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] similar to -2.4, followed by a sudden increase, by about a factor of three, to 39% from {[}Fe/H] similar to -2.4 to {[}Fe/H] similar to -3.7. Although the number of stars known with {[}Fe/H] < -4.0 remains small, the frequency of carbon-enhanced metal-poor (CEMP) stars below this value is around 75%. 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; a roughly constant value. For the main-sequence turnoff stars, we obtain a lower cumulative CEMP frequency, around 10% for {[}Fe/H] <= -2.5, presumably due to the difficulty of identifying CEMP stars among warmer turnoff stars with weak CH G-bands. 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 (vertical bar Z vertical bar < 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. The general rise in the global CEMP frequency at low metallicity is likely due to the transition from the inner-halo to the outer-halo stellar populations with declining metallicity and increasing distance from the plane. (AU)

FAPESP's process: 12/13722-1 - (Re)Discovery and analysis of metal-poor stars in the Milky Way
Grantee:Vinicius Moris Placco
Support type: Scholarships abroad - Research Internship - Post-doctor