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NLTE C and O abundances in RR lyrae stars
Author(s) -
Andrievsky Sergei M.,
Wallerstein George,
Korotin Sergey A.,
Kovtyukh Valery V.,
Khrapaty Sergii V.,
Rydyak Yuri,
Mishenina Tamara V.,
Huang Wenjin
Publication year - 2020
Publication title -
astronomische nachrichten
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.394
H-Index - 63
eISSN - 1521-3994
pISSN - 0004-6337
DOI - 10.1002/asna.202013831
Subject(s) - physics , astrophysics , stars , rr lyrae variable , abundance (ecology) , thermodynamic equilibrium , effective temperature , spectrograph , asymptotic giant branch , spectral line , astronomy , thermodynamics , globular cluster , fishery , biology
The high excitation levels that form the O i and C i lines seen in RR Lyrae stars have long been known not to obey local thermodynamic equilibrium (LTE) statistics. We have observed 21 RR Lyrae and related stars with the Apache Point Observatory echelle spectrograph on the 3.5‐m telescope and, for the first time, have derived abundances using non‐local thermodynamic equilibrium (NLTE) analyses in conjunction with spectral synthesis. In our previous investigation, we determined carbon to be overabundant using an LTE analysis. We now find the carbon abundance to be underabundant relative to solar abundance for stars with [Fe/H] < 0.0 ([C/Fe] < 0 and by implication [C/H] < 0 ). Abundances derived for C using an NLTE analysis are consistent with both main‐sequence stars and red giants. This supports the predictions by He flash hydrodynamic simulations, which predict no convective mixing that might bring carbon produced in the He flash to the atmosphere. For oxygen, we find the dependence of [O/Fe] on [Fe/H] to be similar to other stars with [Fe/H] from 0.0 to −2.8.