Bibcode
Bernard, E. J.; Monelli, M.; Gallart, C.; Aparicio, A.; Cassisi, Santi; Drozdovsky, I.; Hidalgo, S. L.; Skillman, Evan D.; Stetson, Peter B.
Referencia bibliográfica
The Astrophysical Journal, Volume 712, Issue 2, pp. 1259-1276 (2010).
Fecha de publicación:
4
2010
Revista
Número de citas
57
Número de citas referidas
54
Descripción
We present the results of a new search for variable stars in the Local
Group (LG) isolated dwarf galaxy IC 1613, based on 24 orbits of F475W
and F814W photometry from the Advanced Camera for Surveys (ACS) on board
the Hubble Space Telescope. We detected 259 candidate variables in this
field, of which only 13 (all of them bright Cepheids) were previously
known. Out of the confirmed variables, we found 90 RR Lyrae stars, 49
classical Cepheids (including 36 new discoveries), and 38 eclipsing
binary stars for which we could determine a period. The RR Lyrae include
61 fundamental (RRab) and 24 first-overtone (FO, RRc) pulsators, and
five pulsating in both modes simultaneously (RRd). As for the majority
of LG dwarfs, the mean periods of the RRab and RRc (0.611 and 0.334
days, respectively) as well as the fraction of overtone pulsators (f
c = 0.28) place this galaxy in the intermediate regime
between the Oosterhoff types. From their position on the
period-luminosity diagram and light-curve morphology, we can
unambiguously classify 25 and 14 Cepheids as fundamental and FO mode
pulsators, respectively. Another two are clearly second-overtone
Cepheids, the first ones to be discovered beyond the Magellanic Clouds.
Among the remaining candidate variables, five were classified as
δ-Scuti and five as long-period variables. Most of the others are
located on the main sequence, the majority of them likely eclipsing
binary systems, although some present variations similar to pulsating
stars. We estimate the distance to IC 1613 using various methods based
on the photometric and pulsational properties of the Cepheids and RR
Lyrae stars. The values we find are in very good agreement with each
other and with previous estimates based on independent methods. When
corrected to a common reddening of E(B - V) = 0.025 and true Large
Magellanic Cloud (LMC) distance modulus of (m-M)LMC,0 =
18.515 ± 0.085, we find that all the distance determinations from
the literature converge to a common value of (m-M)0 = 24.400
± 0.014 (statistical) or 760 kpc. The parallel WFPC2 field, which
lies within three core radii, was also searched for variable stars. We
discovered nine RR Lyrae stars (four RRab, four RRc, and one RRd) and
two Cepheids, even though the lower signal-to-noise ratio of the
observations did not allow us to measure their periods as accurately as
for the variables in the ACS field of view. We provide their coordinates
and approximate properties for completeness.
Based on observations made with the NASA/ESA Hubble Space Telescope,
obtained at the Space Telescope Science Institute, which is operated by
the Association of Universities for Research in Astronomy, Inc., under
NASA contract NAS5-26555. These observations are associated with program
10505.
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