Bibcode
DOI
Monelli, M.; Pulone, L.; Corsi, C. E.; Castellani, M.; Bono, G.; Walker, A. R.; Brocato, E.; Buonanno, R.; Caputo, F.; Castellani, V.; Dall'Ora, M.; Marconi, M.; Nonino, M.; Ripepi, V.; Smith, H. A.
Referencia bibliográfica
The Astronomical Journal, Volume 126, Issue 1, pp. 218-236.
Fecha de publicación:
7
2003
Número de citas
111
Número de citas referidas
80
Descripción
We present a new (V, B-V) color-magnitude diagram of the Carina dwarf
spheroidal galaxy (dSph) that extends from the tip of the red giant
branch (RGB) down to V~25 mag. Data were collected with the Wide Field
Imager available at the 2.2 m ESO/MPI telescope and cover an area of
~0.3 deg2 around the center of the galaxy. We confirm the
occurrence of a substantial number of old stars with ages around 11 Gyr,
together with an intermediate-age population around 5 Gyr. Moreover, we
also detected a new, well-defined blue plume of young main-sequence
stars with an age, at most, on the order of 1 Gyr. This finding is
further supported by the detection of a sizable sample of anomalous
Cepheids, whose occurrence can be understood in terms of stars with ages
~0.6 Gyr. The evidence for such a young population appears at odds with
current cosmological models, which predict that the most recent star
formation episodes in dSph's should have taken place 2-3 Gyr ago. At
odds with previous results available in the literature, we found that
stars along the RGB of old and intermediate-age stellar populations
indicate a mean metallicity roughly equal to Z=0.0004 ([Fe/H]~-1.7) and
a small dispersion around this value. This finding is further
strengthened by the reduced spread in luminosity of RR Lyrae and
horizontal-branch stars in the old stellar population and of the red
clump in the intermediate-age group. We find evidence of a smooth
spatial distribution of the intermediate-age stellar population (~5
Gyr), which appears more centrally concentrated than the oldest one (~11
Gyr). The radial distribution of the old population appears more clumpy,
with a peak off-center by ~2' when compared with the Carina center. Star
counts show a well-defined ``shoulder'' in the northeast direction along
both the minor and major axes. Current data do not allow us to assess
whether this feature is the break in the slope of star-count profiles
predicted by Johnston, Sigurdsson, & Hernquist.
Based on observations collected at the European Southern Observatory, La
Silla, Chile, on Osservatorio Astronomico di Capodimonte guaranteed
time.