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Title: The Diversity of Chemical Composition: The Impact of Stellar Abundances on the Evolution of Stars and Habitable Zones

 [1];  [2]
  1. Los Alamos National Laboratory
  2. Arizona State University
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
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OSTI Identifier:
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DOE Contract Number:
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Resource Relation:
Conference: American Astronomical Society 231st Winter Meeting ; 2018-01-08 - 2018-01-12 ; Washington D.C., District Of Columbia, United States
Country of Publication:
United States

Citation Formats

Truitt, Amanda Rosendall, and Young, Patrick A. The Diversity of Chemical Composition: The Impact of Stellar Abundances on the Evolution of Stars and Habitable Zones. United States: N. p., 2018. Web.
Truitt, Amanda Rosendall, & Young, Patrick A. The Diversity of Chemical Composition: The Impact of Stellar Abundances on the Evolution of Stars and Habitable Zones. United States.
Truitt, Amanda Rosendall, and Young, Patrick A. 2018. "The Diversity of Chemical Composition: The Impact of Stellar Abundances on the Evolution of Stars and Habitable Zones". United States. doi:.
title = {The Diversity of Chemical Composition: The Impact of Stellar Abundances on the Evolution of Stars and Habitable Zones},
author = {Truitt, Amanda Rosendall and Young, Patrick A.},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2018,
month = 1

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  • Building on previous work, we have expanded our catalog of evolutionary models for stars with variable composition; here we present models for stars of mass 0.5–1.2 M {sub ⊙}, at scaled metallicities of 0.1–1.5 Z {sub ⊙}, and specific C/Fe, Mg/Fe, and Ne/Fe values of 0.58–1.72 C/Fe{sub ⊙}, 0.54–1.84 Mg/Fe{sub ⊙}, and 0.5–2.0 Ne/Fe{sub ⊙}, respectively. We include a spread in abundance values for carbon and magnesium based on observations of their variability in nearby stars; we choose an arbitrary spread in neon abundance values commensurate with the range seen in other low Z elements due to the difficult naturemore » of obtaining precise measurements of neon abundances in stars. As indicated by the results of Truitt et al., it is essential that we understand how differences in individual elemental abundances, and not just the total scaled metallicity, can measurably impact a star’s evolutionary lifetime and other physical characteristics. In that work, we found that oxygen abundances significantly impacted the stellar evolution; carbon, magnesium, and neon are potentially important elements to individually consider due to their relatively high (but also variable) abundances in stars. We present 528 new stellar main-sequence models, and we calculate the time-dependent evolution of the associated habitable zone boundaries for each based on mass, temperature, and luminosity. We also reintroduce the 2 Gyr “Continuously Habitable Zone” (CHZ{sub 2}) as a useful tool to help gauge the habitability potential for a given planetary system.« less
  • Through an analysis of high-resolution, high signal-to-noise data, carbon, nitrogen, and oxygen abundances are investigated in 19 G and K Ib stars. The final analysis yields abundances for 16 of these objects; the other three have to be eliminated due to heavy blending of (C I) with a previously undetected line of FeH. The derived abundances show that, relative to solar values, these stars are heavily deficient in carbon and enhanced in nitrogen, and that there is also a moderate oxygen deficiency. The internal accuracy of the abundances is shown to be about 0.2-0.3 dex.Precise interpretation of the derived abundancesmore » is difficult, as the initial abundance distribution among carbon, nitrogen, and oxygen is uncertain. Assuming reasonable initial values, comparison with evolutionary theory indicates that these objects have been more heavily processed than would be expected on the basis of present calculations. There is a tendency for lower carbon abundances to be associated with low /sup 12/C//sup 13/C ratios.« less
  • Near-IR and IR spectra are analyzed to obtain elemental and isotopic C, N, and O abundance, iron peak abundances, and heavy element s-process abundances for a sample of M, MS, and S giants. The compositions of the M giants are similar to those of G and K giants and consistent with predictions for giants that have deep convective envelopes and so have experienced the first dredge-up. The MS and S giants have compositions that show the signatures of the third dredge-up that occurs in thermally pulsing AGB stars. The sample shows that C-12, a principal product of the He-burning shell,more » has been added to the envelopes of MS and S stars. The C-12 enrichment is correlated with a more marked enrichment of the s-process elements that are predicted to be synthesized when a neutron source is ignited in the He-burning shell. The MS and S giants show a higher N abundance than the M giants, attributed to the expected deep mixing that occurs with the onset of the episodic third dredge-up. 122 refs.« less
  • Atmospheric parameters and oxygen abundances of 825 nearby FGK stars are derived using high-quality spectra and a non-local thermodynamic equilibrium analysis of the 777 nm O I triplet lines. We assign a kinematic probability for the stars to be thin-disk (P {sub 1}), thick-disk (P {sub 2}), and halo (P {sub 3}) members. We confirm previous findings of enhanced [O/Fe] in thick-disk (P {sub 2} > 0.5) relative to thin-disk (P {sub 1} > 0.5) stars with [Fe/H] {approx}< -0.2, as well as a 'knee' that connects the mean [O/Fe]-[Fe/H] trend of thick-disk stars with that of thin-disk members atmore » [Fe/H] {approx}> -0.2. Nevertheless, we find that the kinematic membership criterion fails at separating perfectly the stars in the [O/Fe]-[Fe/H] plane, even when a very restrictive kinematic separation is employed. Stars with 'intermediate' kinematics (P {sub 1} < 0.7, P {sub 2} < 0.7) do not all populate the region of the [O/Fe]-[Fe/H] plane intermediate between the mean thin-disk and thick-disk trends, but their distribution is not necessarily bimodal. Halo stars (P {sub 3} > 0.5) show a large star-to-star scatter in [O/Fe]-[Fe/H], but most of it is due to stars with Galactocentric rotational velocity V < -200 km s{sup -1}; halo stars with V > -200 km s{sup -1} follow an [O/Fe]-[Fe/H] relation with almost no star-to-star scatter. Early mergers with satellite galaxies explain most of our observations, but the significant fraction of disk stars with 'ambiguous' kinematics and abundances suggests that scattering by molecular clouds and radial migration have both played an important role in determining the kinematic and chemical properties of solar neighborhood stars.« less
  • The results of previous calculations of the production of Al-26 and the enhancement of heavy isotopes of Fe by Wolf-Rayet (WR) stars are discussed. Mass fractions of Al-26 in WR ejects and in WR H-rich envelopes are given as a function of stellar mass. It is concluded that the predicted mass of Al-26 in the ISM and its galactic distribution are such that WR stars are expected to be a significant if not the major source of the Al-26. The results suggest that He-22 enhancement must be accompanied by 4-8X enhancement of Fe-57, 20-45X enhancement of Fe-58, and 5-10X enhancementmore » of Co-59. The isotopes of Fe are found to be affected before an appreciable enhancement of Ne-22 occurs. The size of the Ne-22 enhancement depends on the details of the mass-loss history whereas the Fe enhancement does not. 11 references.« less