629 research outputs found
Simulating CCD images of elliptical galaxies
We introduce a procedure developed by the ``Teramo Stellar Populations
Tools'' group (Teramo-SPoT), specifically optimized to obtain realistic
simulations of CCD images of elliptical galaxies.
Particular attention is devoted to include the Surface Brightness Fluctuation
(SBF) signal observed in ellipticals and to simulate the Globular Cluster (GC)
system in the galaxy, and the distribution of background galaxies present in
real CCD frames. In addition to the physical properties of the simulated
objects - galaxy distance and brightness profile, luminosity function of GC and
background galaxies, etc. - the tool presented allows the user to set some of
the main instrumental properties - FoV, zero point magnitude, exposure time,
etc.Comment: Presented at From Stars to Galaxies: Building the Pieces to Build up
the Universe (StarGal 2006), Venice, Italy, 16-20 Oct 200
Evolution of massive stars at very low metallicity including rotation and binary interactions
We discuss recent models on the evolution of massive stars at very low
metallicity including the effects of rotation, magnetic fields and binarity.
Very metal poor stars lose very little mass and angular momentum during the
main sequence evolution, and rotation plays a dominant role in their evolution.
In rapidly rotating massive stars, the rotationally induced mixing time scale
can be even shorter than the nuclear time scale throughout the main sequence.
The consequent quasi-chemically homogeneous evolution greatly differs from the
standard massive star evolution that leads to formation of red giants with
strong chemical stratification. Interesting outcomes of such a new mode of
evolution include the formation of rapidly rotating massive Wolf-Rayet stars
that emit large amounts of ionizing photons, the formation of a long gamma-ray
bursts and a hypernovae, and the production of large amounts of primary
nitrogen. We show that binary interactions can further enhance the effects of
rotation, as mass accretion in a close binary spins up the secondary.Comment: 5 pages, 6 figures, To appear in "Proceedings of First Stars III,"
Eds. Brian W. O'Shea, Alexander Heger & Tom Abe
Long GRBs from binary stars: runaway, Wolf-Rayet progenitors
The collapsar model for long gamma-ray bursts requires a rapidly rotating
Wolf-Rayet star as progenitor. We test the idea of producing rapidly rotating
Wolf-Rayet stars in massive close binaries through mass accretion and
consecutive quasi-chemically homogeneous evolution; the latter had previously
been shown to provide collapsars below a certain metallicity threshold for
single stars. The binary channel presented here may provide a means for massive
stars to obtain the high rotation rates required to evolve quasi-chemically
homogeneous and fulfill the collapsar scenario. Moreover, it suggests that a
possibly large fraction of long gamma-ray bursts occurs in runaway stars.Comment: To appear in the proceedings of the conference "Unsolved problems in
stellar physics" - Cambridge, July 200
On the origin of microturbulence in hot stars
We present results from the first extensive study of convection zones in the
envelopes of hot massive stars, which are caused by opacity peaks associated
with iron and helium ionization. These convective regions can be located very
close to the stellar surface. Recent observations of microturbulence in massive
stars from the VLT-Flames survey are in good agreement with our predictions
concerning the occurrence and the strength of sub-surface convection in hot
stars. We argue further that convection close to the surface may trigger
clumping at the base of the stellar wind of massive stars.Comment: to appear in Comm. in Astroseismology - Proceedings of the 38th
LIAC/HELAS-ESTA/BAG, 200
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