56 research outputs found
Eclipsing Binaries with Possible Light-Time Effect
The period changes of six eclipsing binaries have been studied with focus on
the light-time effect. With the least squares method we also calculated
parameters of such an effect and properties of the unresolved body in these
systems. With these results we discussed the probability of presence of such
bodies in the systems with respect to possible confirmation by another method.
In two systems we also suggested the hypothesis of fourth body or magnetic
activity for explanation of the "second-order variability" after subtraction of
the light-time effect of the third body.Comment: 4 pages, 1 figure, 2 tables, conference proceeding
Inhomogeneous Big Bang Nucleosynthesis and Mutual Ion Diffusion
We present a study of inhomogeneous big bang nucleosynthesis with emphasis on
transport phenomena. We combine a hydrodynamic treatment to a nuclear reaction
network and compute the light element abundances for a range of inhomogeneity
parameters. We find that shortly after annihilation of electron-positron pairs,
Thomson scattering on background photons prevents the diffusion of the
remaining electrons. Protons and multiply charged ions then tend to diffuse
into opposite directions so that no net charge is carried. Ions with Z>1 get
enriched in the overdense regions, while protons diffuse out into regions of
lower density. This leads to a second burst of nucleosynthesis in the overdense
regions at T<20 keV, leading to enhanched destruction of deuterium and lithium.
We find a region in the parameter space at 2.1E-10<eta<5.2E-10 where
constraints
7Li/H<10^{-9.7} and D/H<10^{-4.4} are satisfied simultaneously.Comment: 9 pages, minor changes to match the PRD versio
The Quark-Hadron Phase Transition, QCD Lattice Calculations and Inhomogeneous Big-Bang Nucleosynthesis
We review recent lattice QCD results for the surface tension at the finite
temperature quark-hadron phase transition and discuss their implications on the
possible scale of inhomogeneities. In the quenched approximation the average
distance between nucleating centers is smaller than the diffusion length of a
protron, so that inhomogeneities are washed out by the time nucleosynthesis
sets in. Consequently the baryon density fluctuations formed by a QCD phase
transition in the early universe cannot significantly affect standard big-bang
nucleosynthesis calculations and certainly cannot allow baryons to close the
universe. At present lattice results are inconclusive when dynamical fermions
are included.Comment: 8 pages, LaTe
A cyclical period variation detected in the updated orbital period analysis of TV Columbae
The two CCD photometries of the intermediate polar TV Columbae are made for
obtaining the two updated eclipse timings with high precision. There is an
interval time \sim 17yr since the last mid-eclipse time observed in 1991. Thus,
the new mid-eclipse times can offer an opportunity to check the previous
orbital ephemerides. A calculation indicates that the orbital ephemeris derived
by Augusteijn et al. (1994) should be corrected. Based on the proper linear
ephemeris (Hellier, 1993), the new orbital period analysis suggests a cyclical
period variation in the O-C diagram of TV Columbae. Using Applegate's mechanism
to explain the periodic oscillation in O-C diagram, the required energy is
larger than that a M0-type star can afford over a complete variation period
\sim 31.0(\pm 3.0)yr. Thus, the light travel-time effect indicates that the
tertiary component in TV Columbae may be a dwarf with a low mass, which is near
the mass lower limit \sim 0.08Msun as long as the inclination of the third body
high enough.Comment: 10 pages, 5 figure
An Overview of the 13:8 Mean Motion Resonance between Venus and Earth
It is known since the seminal study of Laskar (1989) that the inner planetary
system is chaotic with respect to its orbits and even escapes are not
impossible, although in time scales of billions of years. The aim of this
investigation is to locate the orbits of Venus and Earth in phase space,
respectively to see how close their orbits are to chaotic motion which would
lead to unstable orbits for the inner planets on much shorter time scales.
Therefore we did numerical experiments in different dynamical models with
different initial conditions -- on one hand the couple Venus-Earth was set
close to different mean motion resonances (MMR), and on the other hand Venus'
orbital eccentricity (or inclination) was set to values as large as e = 0.36 (i
= 40deg). The couple Venus-Earth is almost exactly in the 13:8 mean motion
resonance. The stronger acting 8:5 MMR inside, and the 5:3 MMR outside the 13:8
resonance are within a small shift in the Earth's semimajor axis (only 1.5
percent). Especially Mercury is strongly affected by relatively small changes
in eccentricity and/or inclination of Venus in these resonances. Even escapes
for the innermost planet are possible which may happen quite rapidly.Comment: 14 pages, 11 figures, submitted to CMD
A pilgrimage to gravity on GPUs
In this short review we present the developments over the last 5 decades that
have led to the use of Graphics Processing Units (GPUs) for astrophysical
simulations. Since the introduction of NVIDIA's Compute Unified Device
Architecture (CUDA) in 2007 the GPU has become a valuable tool for N-body
simulations and is so popular these days that almost all papers about high
precision N-body simulations use methods that are accelerated by GPUs. With the
GPU hardware becoming more advanced and being used for more advanced algorithms
like gravitational tree-codes we see a bright future for GPU like hardware in
computational astrophysics.Comment: To appear in: European Physical Journal "Special Topics" : "Computer
Simulations on Graphics Processing Units" . 18 pages, 8 figure
First-order cosmological phase transitions in the radiation dominated era
We consider first-order phase transitions of the Universe in the
radiation-dominated era. We argue that in general the velocity of interfaces is
non-relativistic due to the interaction with the plasma and the release of
latent heat. We study the general evolution of such slow phase transitions,
which comprise essentially a short reheating stage and a longer phase
equilibrium stage. We perform a completely analytical description of both
stages. Some rough approximations are needed for the first stage, due to the
non-trivial relations between the quantities that determine the variation of
temperature with time. The second stage, instead, is considerably simplified by
the fact that it develops at a constant temperature, close to the critical one.
Indeed, in this case the equations can be solved exactly, including
back-reaction on the expansion of the Universe. This treatment also applies to
phase transitions mediated by impurities. We also investigate the relations
between the different parameters that govern the characteristics of the phase
transition and its cosmological consequences, and discuss the dependence of
these parameters with the particle content of the theory.Comment: 38 pages, 3 figures; v2: Minor changes, references added; v3: several
typos correcte
SS Ari: a shallow-contact close binary system
Two CCD epochs of light minimum and a complete R light curve of SS Ari are
presented. The light curve obtained in 2007 was analyzed with the 2003 version
of the W-D code. It is shown that SS Ari is a shallow contact binary system
with a mass ratio and a degree of contact factor f=9.4(\pm0.8%). A
period investigation based on all available data shows that there may exist two
distinct solutions about the assumed third body. One, assuming eccentric orbit
of the third body and constant orbital period of the eclipsing pair results in
a massive third body with and P_3=87.00.278M_{\odot}$. Both of the cases
suggest the presence of an unseen third component in the system.Comment: 28 pages, 9 figures and 5 table
Primordial nuggets survival and QCD pairing
We revisit the problem of boiling and surface evaporation of quark nuggets in
the cosmological quark-hadron transition with the explicit consideration of
pairing between quarks in a color-flavor locked (CFL) state. Assuming that
primordial quark nuggets are actually formed, we analyze the consequences of
pairing on the rates of boiling and surface evaporation in order to determine
whether they could have survived with substantial mass. We find a substantial
quenching of the evaporation + boiling processes, which suggests the survival
of primordial nuggets for the currently considered range of the pairing gap
. Boiling is shown to depend on the competition of an increased
stability window and the suppression of the rate, and is not likely to dominate
the destruction of the nuggets. If surface evaporation dominates, the fate of
the nuggets depend on the features of the initial mass spectrum of the nuggets,
their evaporation rate, and the value of the pairing gap, as shown and
discussed in the text.Comment: 6 pages, 4 figure
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