Bibcode
DOI
Stetson, P. B.; Fiorentino, Giuliana; Bono, Giuseppe; Bernard, Edouard J.; Monelli, M.; Iannicola, Giacinto; Gallart, C.; Ferraro, Ivan
Bibliographical reference
Publications of the Astronomical Society of the Pacific, Volume 126, issue 941, pp.616-641
Advertised on:
7
2014
Citations
51
Refereed citations
43
Description
From archival ground-based images of the Leo I dwarf spheroidal galaxy,
we have identified and characterized the pulsation properties of 164
candidate RR Lyrae variables and 55 candidate anomalous and/or
short-period Cepheids. We have also identified 19 candidate long-period
variable stars and 13 other candidate variables whose physical nature is
unclear, but due to the limitations of our observational material we are
unable to estimate reliable periods for them. On the basis of its RR
Lyrae star population, Leo I is confirmed to be an
Oosterhoff-intermediate type galaxy, like several other dwarf
spheroidals. From the RR Lyrae stars we have derived a range of possible
distance moduli for Leo I : 22.06 ± 0.08 ≲ μ0
≲ 22.25 ± 0.07 mag depending on the metallicity assumed for
the old population ([Fe/H] from -1.43 to -2.15). This is in agreement
with previous independent estimates. We show that in their pulsation
properties, the RR Lyrae stars-representing the oldest stellar
population in the galaxy-are not significantly different from those of
five other nearby, isolated dwarf spheroidal galaxies. A similar result
is obtained when comparing them to RR Lyrae stars in recently discovered
ultra-faint dwarf galaxies. We are able to compare the period
distributions and period-amplitude relations for a statistically
significant sample of ab-type RR Lyrae stars in dwarf galaxies
(˜1300 stars) with those in the Galactic halo field (˜14,000
stars) and globular clusters (˜1000 stars). Field RRLs show a
significant change in their period distribution when moving from the
inner (dG ≲ 14 kpc) to the outer (dG ≳
14 kpc) halo regions. This suggests that the halo formed from (at least)
two dissimilar progenitors or types of progenitor. Considered together,
the RR Lyrae stars in classical dwarf spheroidal and ultra-faint dwarf
galaxies-as observed today-do not appear to follow the well defined
pulsation properties shown by those in either the inner or the outer
Galactic halo, nor do they have the same properties as RR Lyraes in
globular clusters. In particular, the samples of fundamental-mode RR
Lyrae stars in dwarf galaxies seem to lack High Amplitudes and Short
Periods ("HASP": AV≥1.0 mag and P ≲ 0.48 d) when
compared with those observed in the Galactic halo field and globular
clusters. The observed properties of RR Lyrae stars do not support the
idea that currently existing classical dwarf spheroidal and ultra-faint
dwarf galaxies are surviving representative examples of the original
building blocks of the Galactic halo.
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Matteo
Monelli