A Re-Examination of the Cepheid P-L Relation Color-Temperature Relations, Open Clusters, Metallicities)

Details A Re-Examination of the Cepheid P-L Relation Color-Temperature Relations, Open Clusters, Metallicities) A Re-Examination of the Cepheid P-L Relation Color-Temperature Relations, Open Clusters, Metallicities)

Oct 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt........11f&link_type=abstract

Thesis (PHD). THE UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL , Source DAI-B 58/04, p. 1924, Oct 1997, 227 pages.

Computer Science

2

Scientific paper

Using 101 high-S/N, high-resolution spectra of 23 Galactic cepheids, including 15 cepheids in Galactic clusters, we derive (Fe/H) and (α/Fe) abundances. We have done several tests to verify that good abundances can be derived for cepheids. Constancy of (Fe/H) throughout the pulsational cycle indicates a self-consistent temperature scale. We observed 18 of the cepheids at more than one pulsational phase and find excellent agreement among abundance determinations at different temperatures. To check for non-LTE effects, we observed two dwarfs in M 25, which contains the 6.75-day cepheid U Sgr. There are no signs of non-LTE in any of the cepheids except the longest period cepheid (P = 45d). We find a 0.4 dex range in (Fe/H) (1-σ spread of 0.17) and a 0.2 dex range in (α/Fe) among the cepheids. These ranges are not the result of either observational scatter or a Galactic metallicity gradient. Using our spectroscopically derived temperatures and published photometry, we formed cepheid color-temperature relations. Cepheid temperatures will be useful for Baade-Wesselink analyses and for future cepheid abundance analyses. To complement the spectroscopy, we have new optical and infrared photometry of three of the clusters, from which we can derive new, more precise main sequence fitting distances. For NGC 7790, which contains three cepheids CE Cas A & B, and CF Cas, we find (m-M)0 = 12.0 ± 0.2 mag. For NGC 6087, containing S Nor, (m-M)0 = 9.78 ± 0.08 mag and for M 25 (U Sgr), (m-M)0 = 8.95 ± 0.15 mag. For NGC 7790 and NGC 6087 we present the first IR CMD's, each containing about 50 stars near the clusters' centers.

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