Issue |
A&A
Volume 420, Number 2, June III 2004
|
|
---|---|---|
Page(s) | 655 - 663 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20035926 | |
Published online | 28 May 2004 |
The metallicity dependence of the Cepheid PL-relation
1
Instituut voor Sterrenkunde, PACS-ICC, Celestijnenlaan 200B, 3001 Leuven, Belgium
2
ESO, Karl Schwarzschild straße 2, 85748 Garching, Germany
Corresponding author: M. Groenewegen, groen@ster.kuleuven.ac.be
Received:
22
December
2003
Accepted:
5
March
2004
A sample of 37 Galactic, 10 LMC and 6 SMC cepheids is compiled for
which individual metallicity estimates exist and BVIK photometry in
almost all cases. The Galactic cepheids all have an individual
distance estimate available. For the MC objects different sources of
photometry are combined to obtain improved periods and mean
magnitudes. A multi-parameter Period-Luminosity relation is fitted to
the data which also solves for the distance to the LMC and SMC. When
all three galaxies are considered, without metallicity effect, a
significant quadratic term in is found, as previously
observed and also predicted in some theoretical calculations. For the
present sample it is empirically determined that for
linear PL-relations may be adopted, but this restricts the sample to
only 4 LMC and 1 SMC cepheid. Considering the Galactic sample a
metallicity effect is found in the zero point in the VIWK
PL-relation (
or
mag/dex depending on
the in- or exclusion of one object), in the sense that metal-rich
cepheids are brighter. The small significance is mostly due to the
fact that the Galactic sample spans a narrow metallicity range. The
error is to a significant part due to the error in the metallicity
determinations and not to the error in the fit. Including the 5 MC
cepheids broadens the observed metallicity range and a metallity
effect of about
mag/dex in the zero point is found in VIWK, in agreement with some previous empirical estimates, but now
derived using direct metallicity determinations for the cepheids
themselves.
Key words: stars: distances / stars: variables: Cepheids
© ESO, 2004
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