The opal equation of state and low-metallicity isochrones

Brian Chaboyer, Yong Cheol Kim

Research output: Contribution to journalArticle

55 Citations (Scopus)

Abstract

The Yale stellar evolution code has been modified to use the OPAL equation of state tables (Rogers 1994). Stellar models and isochrones were constructed for low-metallicity systems (-2.8 ≤ [Fe/H] ≤ -0.6). Above M ∼ 0.7 M, the isochrones are very similar to those that are constructed using an equation of state that includes the analytical Debye-Hückel correction at high temperatures. The absolute magnitude of the mainsequence turnoff [Mv(TO)] with the OPAL or Debye-Hückel isochrones is about 0.06 mag fainter, at a given age, than Mv(TO) derived from isochrones that do not include the Debye-Hückel correction. As a consequence, globular clusters ages derived using Mv(TO) are reduced by 6%-7% as compared to the ages determined from the standard isochrones. Below M ∼ 0.7 M, the OPAL isochrones are systematically hotter (by approximately 0.04 in B-V) at a given magnitude as compared to the standard, or Debye-Hückel isochrones. However, the lower mass models fall out of the OPAL table range, and this could be the cause of the differences in the location of the lower main sequences.

Original languageEnglish
Pages (from-to)767-773
Number of pages7
JournalAstrophysical Journal
Volume454
Issue number2
DOIs
Publication statusPublished - 1995 Dec 1

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opal
equation of state
metallicity
equations of state
stellar models
stellar evolution
globular clusters
causes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

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abstract = "The Yale stellar evolution code has been modified to use the OPAL equation of state tables (Rogers 1994). Stellar models and isochrones were constructed for low-metallicity systems (-2.8 ≤ [Fe/H] ≤ -0.6). Above M ∼ 0.7 M⊙, the isochrones are very similar to those that are constructed using an equation of state that includes the analytical Debye-H{\"u}ckel correction at high temperatures. The absolute magnitude of the mainsequence turnoff [Mv(TO)] with the OPAL or Debye-H{\"u}ckel isochrones is about 0.06 mag fainter, at a given age, than Mv(TO) derived from isochrones that do not include the Debye-H{\"u}ckel correction. As a consequence, globular clusters ages derived using Mv(TO) are reduced by 6{\%}-7{\%} as compared to the ages determined from the standard isochrones. Below M ∼ 0.7 M⊙, the OPAL isochrones are systematically hotter (by approximately 0.04 in B-V) at a given magnitude as compared to the standard, or Debye-H{\"u}ckel isochrones. However, the lower mass models fall out of the OPAL table range, and this could be the cause of the differences in the location of the lower main sequences.",
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The opal equation of state and low-metallicity isochrones. / Chaboyer, Brian; Kim, Yong Cheol.

In: Astrophysical Journal, Vol. 454, No. 2, 01.12.1995, p. 767-773.

Research output: Contribution to journalArticle

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