380 research outputs found
Nuclei in the Cosmos III Third International Symposium on Nuclear Astrophysics
No full textproceedings book (615 pages) of the Nuclei in the Cosmos n. III symposium held in Assergi, L'Aquila, in 1994. M. Busso is the chairman of the organizing commitee and the first edito
Differential rotation and activity cycles in RS CVn binaries. II - Model results for short and intermediate period members
No full textThree active binaries of the RS CVn class with short period (SV Cam) and
intermediate period (VV Mon and SS Boo) are studied by applying the
statistical procedure of Busso and Scaltriti (1983) and the analytical
method of Busso et al. (1984; Paper I) to a collection of photometric
light curves extending for some years. The behaviour of the wave
distortion for the studied systems can be reproduced fairly well by the
model and allows to determine relevant parameters, such as the angular
velocity at the equator, the rate of differential rotation, the rate of
latitude shear of spots and the latitude of spots at formation. Though
based on a small sample of objects, the results seem to indicate that
short-period and intermediate-period binaries can behave quite similarly
for what concerns spot cycles
Differential rotation and activity cycles in RS CVn binaries. III - UV PISCIUM and UX ARIETIS
No full textNew photoelectric observations of the spotted binaries UX Arietis and UV
Piscium are presented and studied on the basis of a previously
established technique for analyzing unevenly sampled light curves. The
new data, when combined with already published observations, allowed us
to reconstruct the recent evolution of the spot activity in the systems
studied by means of the method described in Busso et al. (1985). The
results confirm the correlations between the differential rotation, the
orbital period, and the duration of spot cycles tentatively established
in that paper
The RS CVn-type binary SV Camelopardalis - Evidence of dark spots from UBV observations and IR fluxes
No full textNew UBV light curves and some infrared JHK observations of the RS
CVn-type binary SV Camelopardalis are presented. New determinations of
primary minimum epochs confirm the presence of a light-time effect, with
a period U = 74.7 yr. The overall shape of the light curve appears to
vary in time by several hundredths of magnitude, due to a distortion
wave whose fast migration causes an inversion in the levels of the
maxima in a few months. IR excesses strongly suggest the presence of
cool regions, in agreement with the common hypothesis that the light
variations are due to starspots. By the method of Vogt (1981) spot
temperatures turn out to be near 3800 K, about 1500 K cooler than the
quiet photosphere. The spot hypothesis is also consistent with the
changes in luminosity observed in the interval 1969-1984, which are
shown to be tightly correlated with the cycles of stellar activity, as
derived by the model of Busso et al. (1984)
On the production of heavy neutron-rich isotopes during He and C burning in massive stars
No full textThe main purpose of this lecture is a re-examination of the yields of
s-elements by massive short-lived stars. He-burning conditions are
reviewed and results are presented for the nucleosynthesis in this
phase. The authors briefly analyse the possibility of n-captures during
carbon burning and discuss the contribution of massive stars to the
enrichment of the interstellar medium in s-elements
La produzione degli elementi chimici nelle stelle. I - L'evoluzione stellare e la nucleosintesi primaria.
No full textNot Availabl
Chemical evolution of the galactic halo. I - Effects of possible mass segregation mechanisms
No full textThe distribution of metals in globular clusters and in the stars of the
bulge component of the Galaxy are reproduced by means of galactic halo
chemical evolution models giving particular attention to the observed
Z(N) relation. Following Hartwick's (1976) demonstration that chemical
distributions of the type observed for population II stars can be
theoretically reproduced if mass is temporarily removed from the
star-forming regions, two alternative mass segregation mechanisms are
proposed to account for this phenomenon: the first being derived from
the different dynamical behavior of the gas and the stars, and the
second from consideration of a star formation law conditioned by the
ionization of early-type stars. Models based on simple schematizations
of the phenomena to which the two mass segregation mechanisms give rise,
as well as on an initial mass function allowing for high M/L ratios, are
found to reproduce observational data for both metal abundances and mass
distributions
Observational constraints to the chemical evolution of the galactic halo from the Space Telescope
No full textResults from numerical computations of the chemical enrichment of the
galactic halo are shown and compared with presently available
observations. A number of problems involved in the models of both
stellar and galactic evolution are reviewed, and key observations, which
will be possible with the various instruments of the Space Telescope,
are discussed
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