For refcode 2010ApJ...715..277B: Retrieve 48 NED objects in this reference. Please click here for ADS abstract
NED Abstract
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Reproduced by permission
2010ApJ...715..277B
Insights into the Cepheid Distance Scale
Bono, G.; Caputo, F.; Marconi, M.; Musella, I.
Abstract. We present a detailed investigation of the Cepheid distance
scale by using both theory and observations. Through the use of pulsation
models for fundamental mode Cepheids, we found that the slope of the
periodluminosity (PL) relation covering the entire period range (0.40 <=
log P <= 2.0) becomes steeper when moving from optical to nearinfrared
(NIR) bands, and that the metallicity dependence of the slope decreases
from the B to the K band. The sign of the metallicity dependence for the
slopes of the PL_V_ and PL_I_ relation is at odds with some recent
empirical estimates. We determined new homogeneous estimates of V and
Iband slopes for 87 independent Cepheid data sets belonging to 48
external galaxies with nebular oxygen abundance 7.5 <= 12 + log (O/H) <=
8.9. By using Cepheid samples including more than 20 Cepheids, the chi^2^
test indicates that the hypothesis of a steepening of the PL_ V,I_
relations with increased metal content can be discarded at the 99% level.
On the contrary, the observed slopes agree with the metallicity trend
predicted by pulsation models, i.e., the slope is roughly constant for
galaxies with 12+log (O/H) < 8.17 and becomes shallower in the metalrich
regime, with confidence levels of 62% and 92%, respectively. The chi^2^
test concerning the hypothesis that the slope does not depend on
metallicity gives confidence levels either similar (PL_V_, 62%) or smaller
(PL_I_, 67%). We investigated the dependence of the periodWesenheit (PW)
relations on the metal content and we found that the slopes of optical and
NIR PW relations in external galaxies are similar to the slopes of Large
Magellanic Cloud (LMC) Cepheids. They also agree with the theoretical
predictions suggesting that the slopes of the PW relations are
independent of the metal content. On this ground, the PW relations
provide a robust method to determine distance moduli relative to the LMC,
but theory and observations indicate that the metallicity dependence of
the zero point in the different passbands has to be taken into account. To
constrain this effect, we compared the independent set of galaxy distances
provided by Rizzi et al. using the tip of the red giant branch with our
homogeneous set of extragalactic Cepheid distances based on the PW
relations. We found that the metallicity correction on distances based on
the PWBV relation is gamma_ B,V_ = 0.52 mag dex^1^, whereas it is
vanishing for the distances based on the PWVI and on the PWJK relations.
These findings fully support Cepheid theoretical predictions.
Key words: Galaxy: disk, Local Group, Magellanic Clouds, stars: distances,
stars: oscillations, stars: variables: Cepheids
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