5 research outputs found
Analisi lineare della stabilitĂ idrodinamica dell'esplosione di una Supernova Ia
In questa tesi viene descritto un modello di base per l'esplosione di una Supernova di tipo Ia. Con il metodo della linearizzazione e dello sviluppo in modi normali, ho eseguito l'analisi della stabilitĂ del fronte d'onda di combustione, in regime di deflagrazione e di detonazione. Questo mi ha permesso di ricavare la relazione di dispersione di stimare i tempi scala con cui si sviluppano le instabilitĂ
New Constraints on Mass-Dependent Disruption of Star Clusters in M51
We use UBVI,Ha images of the Whirlpool galaxy, M51, taken with the ACS and
WFPC2 cameras on the Hubble Space Telescope (HST) to select star clusters, and
to estimate their masses and ages by comparing their observed colors with
predictions from population synthesis models. We construct the mass function of
intermediate age (1-4x10^8 yr) clusters, and find that it is well described by
a power law, psi(M) propto M^beta, with beta=-2.1 +/- 0.2, for clusters more
massive than approximately 6x10^3 Msun. This extends the mass function of
intermediate age clusters in M51 to masses lower by nearly a factor of five
over previous determinations. The mass function does not show evidence for
curvature at either the high or low mass end. This shape indicates that there
is no evidence for the earlier disruption of lower mass clusters compared with
their higher mass counterparts (i.e., no mass-dependent disruption) over the
observed range of masses and ages, or for a physical upper mass limit Mc with
which clusters in M51 can form. These conclusions differ from previous
suggestions based on poorer-quality HST observations. We discuss their
implications for the formation and disruption of the clusters. Ages of clusters
in two "feathers," stellar features extending from the outer portion of a
spiral arm, show that the feather with a larger pitch angle formed earlier, and
over a longer period, than the other.Comment: 24 pages, 7 figures; to be published in ApJ, 727, 8
Star Clusters in Pseudo-Bulges of Spiral Galaxies
We present a study of the properties of the star-cluster systems around
pseudo-bulges of late-type spiral galaxies using a sample of 11 galaxies with
distances from 17 to 37 Mpc. Star clusters are identified from multiband HST
ACS and WFPC2 imaging data by combining detections in 3 bands (F435W and F814W
with ACS and F606W with WFPC2). The photometric data are then compared to
population synthesis models to infer the masses and ages of the star clusters.
Photometric errors and completeness are estimated by means of artificial source
Monte Carlo simulations. Dust extinction is estimated by considering F160W
NICMOS observations of the central regions of the galaxies, augmenting our
wavelength coverage. In all galaxies we identify star clusters with a wide
range of ages, from young (age < 8 Myr) blue clusters, with typical mass of
10^3 Msun to older (age > 100-250 Myr), more massive, red clusters. Some of the
latter might likely evolve into objects similar to the Milky Way's globular
clusters. We compute the specific frequencies for the older clusters with
respect to the galaxy and bulge luminosities. Specific frequencies relative to
the galaxy light appear consistent with the globular cluster specific
frequencies of early-type spirals. We compare the specific frequencies relative
to the bulge light with the globular cluster specific frequencies of dwarf
galaxies, which have a surface-brightness profile that is similar to that of
the pseudo-bulges in our sample. The specific frequencies we derive for our
sample galaxies are higher than those of the dwarf galaxies, supporting an
evolutionary scenario in which some of the dwarf galaxies might be the remnants
of harassed late-type spiral galaxies which hosted a pseudo-bulge.Comment: 34 pages, 9 figures, AJ accepte