7,325 research outputs found
Discontinuous Almost Automorphic Functions and Almost Automorphic Solutions of Differential Equations with Piecewise Constant Argument
In this article we introduce a class of discontinuous almost automorphic
functions which appears naturally in the study of almost automorphic solutions
of differential equations with piecewise constant argument. Their fundamental
properties are used to prove the almost automorphicity of bounded solutions of
a system of differential equations with piecewise constant argument. Due to the
strong discrete character of these equations, the existence of a unique
discrete almost automorphic solution of a non-autonomous almost automorphic
difference system is obtained, for which conditions of exponential dichotomy
and discrete Bi-almost automorphicity are fundamental
A critical appraisal of ATLAS9 and NextGen 5 model atmospheres
The fitting atmosphere parameters (Teff, g, and [Fe/H]) for over 300 stars in
the Gunn & Striker and Jacoby et al. catalogs have been obtained relying on the
Kurucz (1992) ATLAS9 and Hauschildt et al (1999) NextGen5 synthesis models. The
output results are compared, and a critical appraisal of both theoretical codes
is performed.Comment: 2 pages, 2 figures; proceedings of "New Quests in Stellar
Astrophysics: The link between Stars and Cosmology", 26-30 March, 2001,
Puerto Vallarta, Mexico, eds. M. Chavez, A. Bressan, A. Buzzoni & D. Mayya,
to be published by the Kluwer Academic Publisher
Dust and Nebular Emission in Star Forming Galaxies
Star forming galaxies exhibit a variety of physical conditions, from
quiescent normal spirals to the most powerful dusty starbursts. In order to
study these complex systems, we need a suitable tool to analyze the information
coming from observations at all wavelengths. We present a new
spectro-photometric model which considers in a consistent way starlight as
reprocessed by gas and dust. We discuss preliminary results to interpret some
observed properties of VLIRGs.Comment: 8 pages, to be published in "The link between stars and cosmology",
26-30 March, 2001, Puerto Vallarta, Mexico, by Kluwer, eds. M. Chavez, A.
Bressan, A. Buzzoni, and D. Mayy
Deep Studies of the Resolved Stellar Populations in the Outskirts of M31
We discuss the first results from ongoing studies of the resolved stellar
populations in the outskirts of our nearest large neighbour, M31. Deep
HST/WFPC2 archival observations are used to construct colour-magnitude-diagrams
which reach well below the horizontal branch at selected locations in the outer
disk and halo, while a panoramic ground-based imaging survey maps spatial
density variations through resolved star counts to a projected radius of ~50
kpc.Comment: 4 pages, to appear in proc of "New Quests in Stellar Astrophysics:
The Link Between Stars and Cosmology", eds. M. Chavez, A. Bressan, A.
Buzzoni, D. Mayy
Star formation history in the solar neighborhood: the link between stars and cosmology
Using a cosmological galactic evolutionary approach to model the Milky Way,
we calculate the star formation history (SFH) of the solar neighborhood. The
good agreement we obtain with the observational inferences suggests that our
physical model describes accurately the long term/large spatial trends of the
local and global Milky Way SFH. In this model, star formation is triggered by
disk gravitational instabilities and self-regulated by an energy balance in the
ISM. The drivers of the SFH are the cosmological gas infall rate and the gas
surface density determined by the primordial spin parameter. A LambdaCDM
cosmology was used throughout.Comment: 8 pages, uses kluwer.cls. Invited talk, to appear in "New Quests in
Stellar Astrophysics: The link between Stars and Cosmology", eds. M. Chavez,
A. Bressan, A. Buzzoni & D. Mayya, Kluwer Academic Publisher
Spectral Indices of Stars at Super-solar Regime
We derived Lick narrow-band indices for 139 candidate super metal-rich stars
of different luminosity class previously studied in Malagnini et al. (2000).
Indices include Iron Fe50, Fe52, Fe53, and Magnesium Mgb and Mg2 features. By
comparing observations with Kurucz' synthetic model atmospheres, no evidence is
found for non-standard Mg vs. Fe relative abundance (i.e. [Mg/Fe]~ 0, on the
average, for our sample). A comparison with the Worthey et al.(1994) and
Buzzoni et al.(1992, 1994) fitting function predictions for [Fe/H] > 0 is
performed and briefly discussed.Comment: 4 pages, 3 figures; proceedings of "New Quests in Stellar
Astrophysics: The link between Stars and Cosmology", 26-30 March, 2001,
Puerto Vallarta, Mexico, eds. M. Chavez, A. Bressan, A. Buzzoni & D. Mayya,
to be published by the Kluwer Academic Publisher
A Grid of Synthetic Stellar UV Fluxes
We present preliminary results of a large project aimed at creating an
extended theoretical and observational database of stellar spectra in the
ultraviolet wavelength range. This library will consist of IUE spectra at low
and high resolution, and a set of LTE and NLTE theoretical fluxes. A first grid
of 50 model fluxes with solar metallicity, in the wavelength interval 1000 -
4400 AA, is reported here. Calculations are based on the Kurucz (1993) SYNTHE
code. The models span effective temperatures between 10,000 K and 50,000 K, and
a surface gravity in the range 2.5 <= log g <= 5.0 dex.Comment: 2 pages, 1 figure, To appear in proceedings, "New Quests in Stellar
Astrophysics: The Link Between Stars and Cosmology ", March 26-30, 2001, Eds.
M. Chavez, A. Bressan, A. Buzzoni & D. Mayy
Search for B-meson decays to b_1ρ and b_1K^*
We present a search for decays of B mesons to final states with a b_1 meson and a ρ or K^*(892) meson. The search is based on a data sample consisting of 465 million BB̅ pairs collected by the BABAR detector at the SLAC National Accelerator Laboratory. We do not observe any statistically significant signal. The upper limits we set on the branching fractions range from 1.4 to 8.0×10^(-6) at the 90% confidence level, including systematic uncertainties
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Two-fluid temperature-dependent relativistic waves in magnetized streaming pair plasmas
A relativistic two-fluid temperature-dependent approach for a streaming magnetized pair plasma is considered. Such a scenario corresponds to secondary plasmas created at the polar caps of pulsar magnetospheres. In the model the generalized vorticity rather than the magnetic field is frozen into the fluid. For parallel propagation four transverse modes are found. Two are electromagnetic plasma modes which at high temperature become light waves. The remaining two are Alfveacutenic modes split into a fast and slow mode. The slow mode is cyclotron two-stream unstable at large wavelengths and is always subluminous. We find that the instability cannot be suppressed by temperature effects in the limit of large (finite) magnetic field. The fast Alfveacuten mode can be superluminous only at large wavelengths, however it is always subluminous at high temperatures. In this incompressible approximation only the ordinary mode is present for perpendicular propagation. For oblique propagation the dispersion relation is studied for finite and large strong magnetic fields and the results are qualitatively described.Institute for Fusion Studie
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