117 research outputs found
Minimal group codes over alternating groups
In this work we show that every minimal code in a semisimple group algebra
is essential if is a simple group. Since the alternating
group is simple if or , we present some examples of
minimal codes in . For this purpose, if , we present the Wedderburn-Artin decomposition of and
and explicit some of the centrally primitive idempotents of
and .Comment: 16 page
Black Hole Astrophysics : Magnetohydrodynamics on the Kerr Geometry
This work is dedicated to the astrophysics of rotating black holes. The main topic concerns accretion physics in the regime of General Relativistic Magnetohydrodynamics (GRMHD). The behavior of non-radiative accretion flows and outflows on the Kerr space-time is analyzed. Basic equations of conservative GRMHD and aspects of numerical schemes are presented. Relativistic codes and astrophysical simulations validate numerical schemes. A synopsis gives requirements for a robuste GRMHD code. Further developments in GRMHD research are investigated. Another part deals with radiation from accretion disks. Relativistically broadened emission lines from active galactic nuclei and X-ray binaries are calculated by relativistic ray tracing. A new model - based on truncated standard disks - is presented that considers radial drift in accretion flows. Emission lines serve as diagnostic tools to compare parameter studies. Thereby, a classification scheme by line morphology was found: A line profile is triangular, double-horned, bumpy, shoulder-like or double-peaked. Both parts of the work can be connected in further research: results from GRMHD simulations e.g. the velocity field of the flow serve as an input for Kerr ray tracing. Then, realistic spectra are feasible that originate from the vicinity of black holes
The Sagittarius Dwarf spheroidal Galaxy Survey (SDGS) II: The stellar content and constraints on the star formation history
A detailed study of the Star Formation History of the Sgr dSph galaxy is
performed through the analysis of the data from the Sagittarius Dwarf Galaxy
Survey (SDGS; Bellazzini, Ferraro & Buonanno 1999). Accurate statistical
decontamination of the SDGS Color - Magnitude diagrams allow us to obtain many
useful constraints on the age and metal content of the Sgr stellar populations
in three different region of the galaxy.
A coarse metallicity distribution of Sgr stars is derived, ranging from
[Fe/H]~ -2.0 to [Fe/H]~ -0.7, the upper limit being somewhat higher in the
central region of the galaxy. A qualitative global fit to all the observed CMD
features is attempted, and a general scheme for the Star Formation History of
the Sgr is derived. According to this scheme, star formation began at very
early time from a low metal content Inter Stellar Medium and lasted for several
Gyr, coupled with progressive chemical enrichment. The Star Formation Rate
(SFR) had a peak from 8 to 10 gyr ago when the mean metallicity was in the
range -1.3<= [Fe/H] <= -0.7. After that maximum, the SFR rapidly decreased and
very low rate star formation took place until ~1-0.5 Gyr ago.Comment: 21 pages, 12 figures, figg. 1,2,3,5,6,10 and 11 provided in lower
resolution format. For full resolution versions see
http://www.bo.astro.it/bap/BAPhome.html Accepted by MNRA
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