362 research outputs found
Three clusters of the SMC from ACS/WFC HST archive data: NGC 265, K~29 and NGC 290 and their fields
We determine the age, metallicity and initial mass function of three
clusters, namely NGC 265, K~29, NGC 290, located in the main body of the Small
Magellanic Cloud. In addition, we derive the history of star formation in the
companion fields. We make use of ACS/WFC HST archive data. For the clusters,
the age and metallicity are derived fitting the integrated luminosity function
with single synthetic stellar population by means of the minimization.
For the companion fields, the history of star formation is derived using the
minimization together with the downhill-simplex method.For the
clusters we find the following ages and metallicities: NGC 265 has
log(Age)= yr and metallicity (or [Fe/H]=-0.62);
\object{K~29} has log(Age)= yr and metallicity Z= (or
[Fe/H]=-0.75); NGC 290 has log(Age)= yr and metallicity
(or [Fe/H]=-0.75). The superior quality of the data allows the
study of the initial mass function down to M 0.7 M. The initial
mass function turns out to be in agreement with the standard Kroupa model. The
comparison of the NGC 265 luminosity function with the theoretical ones from
stellar models both taking overshoot from the convective core into account and
neglecting it, seems to suggest that a certain amount of convective overshoot
is required. The star formation rate of the field population presents periods
of enhancements at 300-400 Myr, 3-4 Gyr and finally 6 Gyr. However it is
relatively quiescent at ages older than 6 Gyr. This result suggests that at
older ages, the tidal interaction between the Magellanic Clouds and the Milky
Way was not able to trigger significant star formation events.Comment: 20 pages. A&A accepte
Environmental effects on star formation in dwarf galaxies and star clusters
We develop a simple analytical criterion to investigate the role of the
environment on the onset of star formation. We will consider the main external
agents that influence the star formation (i.e. ram pressure, tidal interaction,
Rayleigh-Taylor and Kelvin-Helmholtz instabilities) in a spherical galaxy
moving through an external environment. The theoretical framework developed
here has direct applications to the cases of dwarf galaxies in galaxy clusters
and dwarf galaxies orbiting our Milky Way system, as well as any primordial
gas-rich cluster of stars orbiting within its host galaxy. We develop an
analytic formalism to solve the fluid dynamics equations in a non-inertial
reference frame mapped with spherical coordinates. The two-fluids instability
at the interface between a stellar system and its surrounding hotter and less
dense environment is related to the star formation processes through a set of
differential equations. The solution presented here is quite general, allowing
us to investigate most kinds of orbits allowed in a gravitationally bound
system of stars in interaction with a major massive companion. We present an
analytical criterion to elucidate the dependence of star formation in a
spherical stellar system (as a dwarf galaxy or a globular cluster) on its
surrounding environment useful in theoretical interpretations of numerical
results as well as observational applications. We show how spherical
coordinates naturally enlighten the interpretation of the two-fluids
instability in a geometry that directly applies to astrophysical case. This
criterion predicts the threshold value for the onset of star formation in a
mass vs. size space for any orbit of interest. Moreover, we show for the first
time the theoretical dependencies of the different instability phenomena acting
on a system in a fully analytical way.Comment: ACCEPTED in A&A the 09/09/2014. Changes from ver 1: the non-inertial
linear-response theory for gas instabilities in spherical coordinates is
moved to the Appenidx and will be available only on-lin
Orbital evolution of the Carina dwarf galaxy and self-consistent star formation history determination
We present a new study of the evolution of the Carina dwarf galaxy that
includes a simultaneous derivation of its orbit and star formation history. The
structure of the galaxy is constrained through orbital parameters derived from
the observed distance, proper motions, radial velocity and star formation
history. The different orbits admitted by the large proper motion errors are
investigated in relation to the tidal force exerted by an external potential
representing the Milky Way (MW). Our analysis is performed with the aid of
fully consistent N-body simulations that are able to follow the dynamics and
the stellar evolution of the dwarf system in order to determine
self-consistently the star formation history of Carina. We find a star
formation history characterized by several bursts, partially matching the
observational expectation. We find also compatible results between dynamical
projected quantities and the observational constraints. The possibility of a
past interaction between Carina and the Magellanic Clouds is also separately
considered and deemed unlikely.Comment: Accepted in A&
Testing intermediate-age stellar evolution models with VLT photometry of LMC clusters. I. The data
This is the first of a series of three papers devoted to the calibration of a
few parameters of crucial importance in the modeling of the evolution of
intermediate-mass stars, with special attention to the amount of convective
core overshoot. To this end we acquired deep V and R photometry for three
globular clusters of the Large Magellanic Cloud (LMC), namely NGC 2173, SL 556
and NGC 2155, in the age interval 1-3 Gyr. In this first paper, we describe the
aim of the project, the VLT observations and data reduction, and we make
preliminary comparisons of the color-magnitude diagrams with both Padova and
Yonsei-Yale isochrones. Two following papers in this series present the results
of a detailed analysis of these data, independently carried out by members of
the Yale and Padova stellar evolution groups. This allows us to compare both
sets of models and discuss their main differences, as well as the systematic
effects that they would have to the determination of the ages and metallicities
of intermediate-age single stellar populations.Comment: 27 pages with 10 figures. Accepted by the Astronomical Journa
- …