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Title: DIRECT EVALUATION OF THE HELIUM ABUNDANCES IN OMEGA CENTAURI

Abstract

A direct measure of the helium abundances from the near-infrared transition of He I at 1.08 {mu}m is obtained for two nearly identical red giant stars in the globular cluster Omega Centauri. One star exhibits the He I line; the line is weak or absent in the other star. Detailed non-local thermal equilibrium semi-empirical models including expansion in spherical geometry are developed to match the chromospheric H{alpha}, H{beta}, and Ca II K lines, in order to predict the helium profile and derive a helium abundance. The red giant spectra suggest a helium abundance of Y {<=} 0.22 (LEID 54064) and Y = 0.39-0.44 (LEID 54084) corresponding to a difference in the abundance {Delta}Y {>=} 0.17. Helium is enhanced in the giant star (LEID 54084) that also contains enhanced aluminum and magnesium. This direct evaluation of the helium abundances gives observational support to the theoretical conjecture that multiple populations harbor enhanced helium in addition to light elements that are products of high-temperature hydrogen burning. We demonstrate that the 1.08 {mu}m He I line can yield a helium abundance in cool stars when constraints on the semi-empirical chromospheric model are provided by other spectroscopic features.

Authors:
Publication Date:
OSTI Identifier:
22136575
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal Letters
Additional Journal Information:
Journal Volume: 773; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 2041-8205
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ALUMINIUM; HELIUM; HYDROGEN BURNING; LIMITING VALUES; MAGNESIUM; RED GIANT STARS; SPECTRA; SPHERICAL CONFIGURATION; STAR CLUSTERS; THERMAL EQUILIBRIUM

Citation Formats

Dupree, A. K., and Avrett, E. H., E-mail: dupree@cfa.harvard.edu, E-mail: eavrett@cfa.harvard.edu. DIRECT EVALUATION OF THE HELIUM ABUNDANCES IN OMEGA CENTAURI. United States: N. p., 2013. Web. doi:10.1088/2041-8205/773/2/L28.
Dupree, A. K., & Avrett, E. H., E-mail: dupree@cfa.harvard.edu, E-mail: eavrett@cfa.harvard.edu. DIRECT EVALUATION OF THE HELIUM ABUNDANCES IN OMEGA CENTAURI. United States. https://doi.org/10.1088/2041-8205/773/2/L28
Dupree, A. K., and Avrett, E. H., E-mail: dupree@cfa.harvard.edu, E-mail: eavrett@cfa.harvard.edu. 2013. "DIRECT EVALUATION OF THE HELIUM ABUNDANCES IN OMEGA CENTAURI". United States. https://doi.org/10.1088/2041-8205/773/2/L28.
@article{osti_22136575,
title = {DIRECT EVALUATION OF THE HELIUM ABUNDANCES IN OMEGA CENTAURI},
author = {Dupree, A. K. and Avrett, E. H., E-mail: dupree@cfa.harvard.edu, E-mail: eavrett@cfa.harvard.edu},
abstractNote = {A direct measure of the helium abundances from the near-infrared transition of He I at 1.08 {mu}m is obtained for two nearly identical red giant stars in the globular cluster Omega Centauri. One star exhibits the He I line; the line is weak or absent in the other star. Detailed non-local thermal equilibrium semi-empirical models including expansion in spherical geometry are developed to match the chromospheric H{alpha}, H{beta}, and Ca II K lines, in order to predict the helium profile and derive a helium abundance. The red giant spectra suggest a helium abundance of Y {<=} 0.22 (LEID 54064) and Y = 0.39-0.44 (LEID 54084) corresponding to a difference in the abundance {Delta}Y {>=} 0.17. Helium is enhanced in the giant star (LEID 54084) that also contains enhanced aluminum and magnesium. This direct evaluation of the helium abundances gives observational support to the theoretical conjecture that multiple populations harbor enhanced helium in addition to light elements that are products of high-temperature hydrogen burning. We demonstrate that the 1.08 {mu}m He I line can yield a helium abundance in cool stars when constraints on the semi-empirical chromospheric model are provided by other spectroscopic features.},
doi = {10.1088/2041-8205/773/2/L28},
url = {https://www.osti.gov/biblio/22136575}, journal = {Astrophysical Journal Letters},
issn = {2041-8205},
number = 2,
volume = 773,
place = {United States},
year = {Tue Aug 20 00:00:00 EDT 2013},
month = {Tue Aug 20 00:00:00 EDT 2013}
}