Publication Abstracts

Stothers 1988

Stothers, R.B., 1988: Abundance effects on the Cepheid distance scale. Astrophys. J., 329, 712-719, doi:10.1086/166415.

A new investigation is made of the dependence of the period-luminosity (PL) and period-luminosity-color (PLC) relations on the helium (Y) and metal (Z) abundances in classical Cepheids. For consistency in overall approach and in error estimates, theoretical data alone have been used. These data come from stellar evolution, atmosphere, and pulsation theory. To enhance the accuracy, relative quantities have been adopted to the exclusion of absolute quantities, and numerous published results for each quantity have been averaged before use. Most important of all, composition dependences have been assigned to all quantitites. The results therefore represent a true theoretical prediction.

A major quantitative result is that the PLC relation in B, V magnitudes is at least 5 times more sensitive to chemical composition than is the PL relation, whose dependence is δMv(PL) — 0.5δY - 2.8δZ at a fixed period. If the PL relation is adopted and the helium abundance is held fixed, a Cepheid with Z = 0.005 should be fainter than one with Z = 0.02 by ∼0.04 mag, a result which falls between Iben and Renzini's value of zero and Gascoigne's value of 0.1-0.2 mag but is small in any case. Since the slope of the predicted PL relation is independent of chemical composition, the PL relation can be considered to be effectively universal. Supporting observational evidence consists of (1) the near invariance of the visual absolute magnitude difference between Cepheids with 6 day period and RR Lyrae stars in the Small Magellanic Cloud. Large Magellanic Cloud, and Galaxy, and (2) the agreement between observed and predicted slopes of the PL relations in the three galaxies. Distances to classical Cepheids, however, must be corrected for interstellar extinction, the amount of which can be much more sensitive to metal abundance than is the PL relation itself, if Cepheid colors are used to drive the reddening. Theoretical results are also presented for the bolometric PL relation, whose slope and dependence on metal abundance should be roughly applicable to infrared observations of Cepheids.

Distance moduli of the Magellanic Clouds, corrected for abundance effects, are (m-M)0 = 18.51±0.06 (Large Cloud) and (m-M)0 = 18.80±0.06 (Small Cloud).

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BibTeX Citation

  author={Stothers, R. B.},
  title={Abundance effects on the Cepheid distance scale},
  journal={Astrophysical Journal},

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RIS Citation

ID  - st06500y
AU  - Stothers, R. B.
PY  - 1988
TI  - Abundance effects on the Cepheid distance scale
JA  - Astrophys. J.
JO  - Astrophysical Journal
VL  - 329
SP  - 712
EP  - 719
DO  - 10.1086/166415
ER  -

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