Publication Abstracts

Stothers 1983

Stothers, R., 1983: A new calibration of the extragalactic distance scale using Cepheids and RR Lyrae stars. Astrophys. J., 274, 20-30, doi:10.1086/161422.

Visual absolute magnitudes of classical Cepheids, metal-poor RR Lyraestars, and short-period type II Cepheids have been determined with very high precision by combining a large number of old and new astrophysical data. Five independent methods (four of them observational and one theoretical) have been successfully used: (1) secular and statistical parallaxes; (2) moving-group parallaxes; (3) cluster main-sequence fitting; (4) the Baade-Wesselink method and its modifications; and (5) light-curve and velocity-curve fitting (theoretical method). It is shown that none of the methods depends for its validity on the (very uncertain) Hyades cluster distance modulus. The following results are obtained: for classical Cepheids, ⟨Mν⟩(0.8) = -3.62 based on ⟨Mν⟩ = -1.21-3.01 log P; for metal-poor RR Lyrae stars, ⟨Mν⟩ = 0.61; and for normal 1-3 day type II Cepheids, ⟨Mν⟩ = -0.47. The mean error in each case is ±0.15 mag as estimated from the scatter among all the determinations used for each class of variable star, or ±0.10 mag as derived from the scatter among the means of the determinations based on the various methods used for each class of variable star. These estimates include, therefore, both accidental and systematic errors.

External as well as internal consistency of the absolute magnitudes has been checked by intercomparing the results based on (a) the four independent absolute observational methods; (b) the independent differential data available for stars in the Large Magellanic Cloud, Small Magellanic Cloud, and galactic globular clusters; and (c) the independently generated theoretical data. Only one significant discrepancy emerged: the theoretically predicted absolute magnitudes for classical Cepheids are too bright by 0.5 mag (a 4σ discrepancy), which is possibly a result of nonuniqueness of the light-curve and velocity-curve fitting technique for these stars, but is surely also connected with their well-known "mass discrepancy." It is found that the empirical period-luminosity relation for classical Cepheids is probably universal, i.e., insensitive to chemical composition, and that it is now well established from the large number of Cepheid members of galactic star groups.

Since the zero point of the distance scale has been uniquely determined, classical Cepheids and RR Lyrae stars now provide essentially identical distances to nearby galaxies: to the Large Magellanic Cloud, (m - M)0 = 18.5±0.1; to the Small Magellanic Cloud, (m - M)0 = 18.8±0.1; and to the center of our Galaxy, R0 = 8.6±0.5 kpc. The major uncertainty in these values lies in the correction for interstellar extinction.

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BibTeX Citation

  author={Stothers, R.},
  title={A new calibration of the extragalactic distance scale using Cepheids and RR Lyrae stars},
  journal={Astrophysical Journal},

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RIS Citation

ID  - st02810r
AU  - Stothers, R.
PY  - 1983
TI  - A new calibration of the extragalactic distance scale using Cepheids and RR Lyrae stars
JA  - Astrophys. J.
JO  - Astrophysical Journal
VL  - 274
SP  - 20
EP  - 30
DO  - 10.1086/161422
ER  -

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