15,130 research outputs found
Collapse of Primordial Clouds
We present here studies of collapse of purely baryonic Population III objects
with masses ranging from to . A spherical Lagrangian
hydrodynamic code has been written to study the formation and evolution of the
primordial clouds, from the beginning of the recombination era () until the redshift when the collapse occurs. All the relevant processes
are included in the calculations, as well as, the expansion of the Universe. As
initial condition we take different values for the Hubble constant and for the
baryonic density parameter (considering however a purely baryonic Universe), as
well as different density perturbation spectra, in order to see their influence
on the behavior of the Population III objects evolution. We find, for example,
that the first mass that collapses is for ,
and with the mass scale . For
we obtain for the first
mass that collapses. The cooling-heating and photon drag processes have a key
role in the collapse of the clouds and in their thermal history. Our results
show, for example, that when we disregard the Compton cooling-heating, the
collapse of the objects with masses occurs earlier. On
the other hand, disregarding the photon drag process, the collapse occurs at a
higher redshift.Comment: 10 pages, MN plain TeX macros v1.6 file, 9 PS figures. Also available
at http://www.iagusp.usp.br/~oswaldo (click "OPTIONS" and then "ARTICLES").
MNRAS in pres
Collapse of Primordial Clouds II. The Role of Dark Matter
In this article we extend the study performed in our previous article on the
collapse of primordial objects. We here analyze the behavior of the physical
parameters for clouds ranging from to . We
studied the dynamical evolution of these clouds in two ways: purely baryonic
clouds and clouds with non-baryonic dark matter included. We start the
calculations at the beginning of the recombination era, following the evolution
of the structure until the collapse (that we defined as the time when the
density contrast of the baryonic matter is greater than ). We analyze the
behavior of the several physical parameters of the clouds (as, e.g., the
density contrast and the velocities of the baryonic matter and the dark matter)
as a function of time and radial position in the cloud. In this study all
physical processes that are relevant to the dynamical evolution of the
primordial clouds, as for example photon-drag (due to the cosmic background
radiation), hydrogen molecular production, besides the expansion of the
Universe, are included in the calculations. In particular we find that the
clouds, with dark matter, collapse at higher redshift when we compare the
results with the purely baryonic models. As a general result we find that the
distribution of the non-baryonic dark matter is more concentrated than the
baryonic one. It is important to stress that we do not take into account the
putative virialization of the non-baryonic dark matter, we just follow the time
and spatial evolution of the cloud solving its hydrodynamical equations. We
studied also the role of the cooling-heating processes in the purely baryonic
clouds.Comment: 8 pages, MN plain TeX macros v1.6 file, 13 PS figures. Also available
at http://www.iagusp.usp.br/~oswaldo (click "OPTIONS" and then "ARTICLES").
MNRAS in pres
Stable retrograde orbits around the triple system 2001 SN263
The NEA 2001 SN263 is the target of the ASTER MISSION - First Brazilian Deep
Space Mission. Araujo et al. (2012), characterized the stable regions around
the components of the triple system for the planar and prograde cases. Knowing
that the retrograde orbits are expected to be more stable, here we present a
complementary study. We now considered particles orbiting the components of the
system, in the internal and external regions, with relative inclinations
between , i.e., particles with retrograde
orbits. Our goal is to characterize the stable regions of the system for
retrograde orbits, and then detach a preferred region to place the space probe.
For a space mission, the most interesting regions would be those that are
unstable for the prograde cases, but stable for the retrograde cases. Such
configuration provide a stable region to place the mission probe with a
relative retrograde orbit, and, at the same time, guarantees a region free of
debris since they are expected to have prograde orbits. We found that in fact
the internal and external stable regions significantly increase when compared
to the prograde case. For particles with and , we found
that nearly the whole region around Alpha and Beta remain stable. We then
identified three internal regions and one external region that are very
interesting to place the space probe. We present the stable regions found for
the retrograde case and a discussion on those preferred regions. We also
discuss the effects of resonances of the particles with Beta and Gamma, and the
role of the Kozai mechanism in this scenario. These results help us understand
and characterize the stability of the triple system 2001 SN263 when retrograde
orbits are considered, and provide important parameters to the design of the
ASTER mission.Comment: 11 pages, 8 figures. Accepted for publication in MNRAS - 2015 March
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