Giuliana Fiorentino, Matteo Monelli
Context: The properties of variable stars can give independent constraints on
the star formation history of the host galaxy, through the determination of the
age and the metallicity of the parent population. Aims: We investigate the
pulsation properties of 84 Anomalous Cepheids (ACs) detected by the OGLE-III
survey in the Large Magellanic Cloud (LMC), in order to understand the
formation mechanism and the characteristics of the parent population they
originated from. Methods: We used updated theoretical pulsation scenario to
derive the mass and the pulsation mode of each AC in the sample. We also
discuss, by means of a Kolmogorov-Smirnov test, the spatial distribution of the
ACs, in comparison with that of other groups of variable stars, and connect
their properties with the star formation history of the LMC. Results: We find
that the ACs' mean mass is $1.2 \pm 0.2 M_{\odot}$. We show that ACs do not
follow the same spatial distribution of classical Cepheids. This, and the fact
that their period-luminosity relations are different, provides further support
to the hypothesis that ACs are not the extension to low luminosity of classical
Cepheids. The spatial distribution of ACs is also different from that of
bona-fide tracers of the old population, such as RR Lyrae stars and population
II Cepheids. We therefore suggest that the majority of ACs in the LMC is made
of intermediate-age (1-6\,Gyr), metal-poor single stars. Finally, we
investigate the relation between the frequency of ACs and the luminosity of the
host galaxy, disclosing that purely old system follow a very tight relation,
and that galaxies with important intermediate-age and young star formation tend
to have an excess of ACs, in agreement with the fact that they host ACs formed
via both single and binary stars channels.
View original:
http://arxiv.org/abs/1202.2752
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