dc.contributor.author |
Maas, T |
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dc.contributor.author |
Giridhar, S |
|
dc.contributor.author |
Lambert, D. L |
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dc.date.accessioned |
2008-03-06T07:35:38Z |
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dc.date.available |
2008-03-06T07:35:38Z |
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dc.date.issued |
2007-09 |
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dc.identifier.citation |
The Astrophysical Journal, Vol. 666, pp. 378 – 392 |
en |
dc.identifier.uri |
http://hdl.handle.net/2248/2135 |
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dc.description.abstract |
Abundance analyses from high-resolution optical spectra are presented for 19 type II Cepheids in the Galactic field. The sample includes both short-period (BL Her) and long-period (W Vir) stars. This is the first extensive abundance analysis of these variables. The C, N, and O abundances with similar spreads for the BL Her and W Vir show evidence for an atmosphere contaminated with 3α process and CN-cycling products. A notable anomaly of the BL Her stars is an overabundance of Na by a factor of about 5 relative to their presumed initial abundances. This overabundance is not seen in the W Vir stars. The abundance anomalies running from mild to extreme in W Vir stars but not seen in the BL Her stars are attributed to dust-gas separation that provides an atmosphere deficient in elements of high condensation temperature, notably, Al, Ca, Sc, Ti, and s-process elements. Such anomalies have previously been seen among RV Tau stars which represent a long-period extension of the variability enjoyed by the type II Cepheids. Comments are offered on how the contrasting abundance anomalies of BL Her and W Vir stars may be explained in terms of the stars’ evolution from the blue horizontal branch. |
en |
dc.format.extent |
538279 bytes |
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dc.format.mimetype |
application/pdf |
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dc.language.iso |
en |
en |
dc.publisher |
University of Chicago Press |
en |
dc.relation.uri |
http://www.journals.uchicago.edu/doi/abs/10.1086/520081 |
en |
dc.relation.uri |
http://arxiv.org/abs/0706.2029 |
en |
dc.subject |
stars: abundances—stars: variables |
en |
dc.title |
The Chemical Compositions of the Type II Cepheids-The BL Herculis and W Virginis Variables |
en |
dc.type |
Article |
en |