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Title: STELLAR NUCLEOSYNTHESIS IN THE HYADES OPEN CLUSTER

Abstract

We report a comprehensive light-element (Li, C, N, O, Na, Mg, and Al) abundance analysis of three solar-type main sequence (MS) dwarfs and three red giant branch (RGB) clump stars in the Hyades open cluster using high-resolution and high signal-to-noise spectroscopy. The abundances have been derived in a self-consistent fashion, and for each group (MS or RGB), the CNO abundances are found to be in excellent star-to-star agreement. Using the dwarfs to infer the initial composition of the giants, the combined abundance patterns confirm that the giants have undergone the first dredge-up and that material processed by the CN cycle has been mixed to the surface layers. The observed abundances are compared to predictions of a standard stellar model based on the Clemson-American University of Beirut (CAUB) stellar evolution code. The model reproduces the observed evolution of the N and O abundances, as well as the previously derived {sup 12}C/{sup 13}C ratio, but it fails to predict by a factor of 1.5 the observed level of {sup 12}C depletion. A similar discord appears to exist in previously reported observed and modeled C abundances of giants in the Galactic disk. Random uncertainties in the mean abundances and uncertainties related to possiblemore » systematic errors in the Hyades dwarf and giant parameter scales cannot account for the discrepancy in the observed and modeled abundances. Li abundances are derived to determine if noncanonical extra mixing, like that seen in low-mass metal-poor giants, has occurred in the Hyades giants. The Li abundance of the giant {gamma} Tau is in good accord with the predicted level of surface Li dilution, but a {approx}0.35 dex spread in the giant Li abundances is found and cannot be explained by the stellar model. Possible sources of the spread are discussed; however, it is apparent that the differential mechanism responsible for the Li dispersion must be unrelated to the uniformly low {sup 12}C abundances of the giants. Na, Mg, and Al abundances are derived as an additional test of our stellar model. All three elements are found to be overabundant by 0.2-0.5 dex in the giants relative to the dwarfs. Such large enhancements of these elements are not predicted by the stellar model, and non-LTE effects significantly larger (and, in some cases, of opposite sign) than those implied by extant literature calculations are the most likely cause.« less

Authors:
 [1];
  1. National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)
Publication Date:
OSTI Identifier:
21313655
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 701; Journal Issue: 1; Other Information: DOI: 10.1088/0004-637X/701/1/837; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE; ABUNDANCE; ATMOSPHERES; CARBON 12; CARBON 13; DILUTION; DISPERSIONS; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; SPECTROSCOPY; STAR EVOLUTION; STARS

Citation Formats

Schuler, Simon C, King, Jeremy R, and The, L.-S. STELLAR NUCLEOSYNTHESIS IN THE HYADES OPEN CLUSTER. United States: N. p., 2009. Web. doi:10.1088/0004-637X/701/1/837; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Schuler, Simon C, King, Jeremy R, & The, L.-S. STELLAR NUCLEOSYNTHESIS IN THE HYADES OPEN CLUSTER. United States. https://doi.org/10.1088/0004-637X/701/1/837; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)
Schuler, Simon C, King, Jeremy R, and The, L.-S. 2009. "STELLAR NUCLEOSYNTHESIS IN THE HYADES OPEN CLUSTER". United States. https://doi.org/10.1088/0004-637X/701/1/837; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
@article{osti_21313655,
title = {STELLAR NUCLEOSYNTHESIS IN THE HYADES OPEN CLUSTER},
author = {Schuler, Simon C and King, Jeremy R and The, L.-S.},
abstractNote = {We report a comprehensive light-element (Li, C, N, O, Na, Mg, and Al) abundance analysis of three solar-type main sequence (MS) dwarfs and three red giant branch (RGB) clump stars in the Hyades open cluster using high-resolution and high signal-to-noise spectroscopy. The abundances have been derived in a self-consistent fashion, and for each group (MS or RGB), the CNO abundances are found to be in excellent star-to-star agreement. Using the dwarfs to infer the initial composition of the giants, the combined abundance patterns confirm that the giants have undergone the first dredge-up and that material processed by the CN cycle has been mixed to the surface layers. The observed abundances are compared to predictions of a standard stellar model based on the Clemson-American University of Beirut (CAUB) stellar evolution code. The model reproduces the observed evolution of the N and O abundances, as well as the previously derived {sup 12}C/{sup 13}C ratio, but it fails to predict by a factor of 1.5 the observed level of {sup 12}C depletion. A similar discord appears to exist in previously reported observed and modeled C abundances of giants in the Galactic disk. Random uncertainties in the mean abundances and uncertainties related to possible systematic errors in the Hyades dwarf and giant parameter scales cannot account for the discrepancy in the observed and modeled abundances. Li abundances are derived to determine if noncanonical extra mixing, like that seen in low-mass metal-poor giants, has occurred in the Hyades giants. The Li abundance of the giant {gamma} Tau is in good accord with the predicted level of surface Li dilution, but a {approx}0.35 dex spread in the giant Li abundances is found and cannot be explained by the stellar model. Possible sources of the spread are discussed; however, it is apparent that the differential mechanism responsible for the Li dispersion must be unrelated to the uniformly low {sup 12}C abundances of the giants. Na, Mg, and Al abundances are derived as an additional test of our stellar model. All three elements are found to be overabundant by 0.2-0.5 dex in the giants relative to the dwarfs. Such large enhancements of these elements are not predicted by the stellar model, and non-LTE effects significantly larger (and, in some cases, of opposite sign) than those implied by extant literature calculations are the most likely cause.},
doi = {10.1088/0004-637X/701/1/837; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)},
url = {https://www.osti.gov/biblio/21313655}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 701,
place = {United States},
year = {Mon Aug 10 00:00:00 EDT 2009},
month = {Mon Aug 10 00:00:00 EDT 2009}
}