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Title: Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. I. Carbon Abundance Estimation and Frequency of CEMP Stars

Abstract

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.more » 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]« less

Authors:
 [1];  [2];  [3];  [4];  [5];  [6];  [7];  [8];  [9];  [10];  [11]
  1. NMSU, Las Cruces
  2. Michigan State U., JINA
  3. Brussels U.
  4. U. Montpellier 2, LUPM
  5. Lick Observ.
  6. Chicago U.
  7. Fermilab
  8. Padua Observ.
  9. Bangalore, Indian Inst. Astrophys.
  10. Sao Paulo U., IAG
  11. Macquarie U.
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP)
OSTI Identifier:
1347937
Report Number(s):
arXiv:1310.3276; FERMILAB-PUB-13-655-AE
Journal ID: ISSN 0004-6256; 1305745
DOE Contract Number:  
AC02-07CH11359
Resource Type:
Journal Article
Journal Name:
The Astronomical Journal
Additional Journal Information:
Journal Volume: 146; Journal Issue: 5; Journal ID: ISSN 0004-6256
Publisher:
American Institute of Physics
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS

Citation Formats

Lee, Young Sun, Beers, Timothy C., Masseron, Thomas, Plez, Bertrand, Rockosi, Constance M., Sobeck, Jennifer, Yanny, Brian, Lucatello, Sara, Sivarani, Thirupathi, Placco, Vinicius M., and Carollo, Daniela. Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. I. Carbon Abundance Estimation and Frequency of CEMP Stars. United States: N. p., 2013. Web. doi:10.1088/0004-6256/146/5/132.
Lee, Young Sun, Beers, Timothy C., Masseron, Thomas, Plez, Bertrand, Rockosi, Constance M., Sobeck, Jennifer, Yanny, Brian, Lucatello, Sara, Sivarani, Thirupathi, Placco, Vinicius M., & Carollo, Daniela. Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. I. Carbon Abundance Estimation and Frequency of CEMP Stars. United States. https://doi.org/10.1088/0004-6256/146/5/132
Lee, Young Sun, Beers, Timothy C., Masseron, Thomas, Plez, Bertrand, Rockosi, Constance M., Sobeck, Jennifer, Yanny, Brian, Lucatello, Sara, Sivarani, Thirupathi, Placco, Vinicius M., and Carollo, Daniela. 2013. "Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. I. Carbon Abundance Estimation and Frequency of CEMP Stars". United States. https://doi.org/10.1088/0004-6256/146/5/132. https://www.osti.gov/servlets/purl/1347937.
@article{osti_1347937,
title = {Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. I. Carbon Abundance Estimation and Frequency of CEMP Stars},
author = {Lee, Young Sun and Beers, Timothy C. and Masseron, Thomas and Plez, Bertrand and Rockosi, Constance M. and Sobeck, Jennifer and Yanny, Brian and Lucatello, Sara and Sivarani, Thirupathi and Placco, Vinicius M. and Carollo, Daniela},
abstractNote = {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]},
doi = {10.1088/0004-6256/146/5/132},
url = {https://www.osti.gov/biblio/1347937}, journal = {The Astronomical Journal},
issn = {0004-6256},
number = 5,
volume = 146,
place = {United States},
year = {Thu Oct 17 00:00:00 EDT 2013},
month = {Thu Oct 17 00:00:00 EDT 2013}
}