157,182 research outputs found
The YNEV stellar evolution and oscillation code
We have developed a new stellar evolution and oscillation code YNEV, which
calculates the structures and evolutions of stars, taking into account hydrogen
and helium burning. A nonlocal turbulent convection theory and an updated
overshoot mixing model are optional in this code. The YNEV code can evolve low-
and intermediate-mass stars from pre-main sequence (PMS) to thermal pulsing
asymptotic branch giant (TP-AGB) or white dwarf. The YNEV oscillation code
calculates the eigenfrequencies and eigenfunctions of the adiabatic
oscillations of given stellar structure. The input physics and the numerical
scheme adopted in the code are introduced in this paper. The examples of solar
models, stellar evolutionary tracks of low- and intermediate-mass stars with
different convection theory (i.e., mixing-length theory (MLT) and the nonlocal
turbulent convection theory), and stellar oscillations are shown.Comment: 18 pages, 14 figures, accepted for publication in the Research in
Astronomy and Astrophysics (RAA
A simple scheme to implement a nonlocal turbulent convection model for the convective overshoot mixing
The classical 'ballistic' overshoot models show some contradictions and are
not consistence with numerical simulations and asteroseismic studies.
Asteroseismic studies imply that overshoot is a weak mixing process. Diffusion
model is suitable to deal with it. The form of diffusion coefficient in a
diffusion model is crucial. Because the overshoot mixing is related to the
convective heat transport (i.e., entropy mixing), there should be a similarity
between them. A recent overshoot mixing model shows consistence between
composition mixing and entropy mixing in overshoot region. A prerequisite to
apply the model is to know the dissipation rate of turbulent kinetic energy.
The dissipation rate can be worked out by solving turbulent convection models
(TCMs). But it is difficult to apply TCMs because of some numerical problems
and the enormous time cost. In order to find a convenient way, we have used the
asymptotical solution and simplified the TCM to be a single linear equation for
turbulent kinetic energy. This linear model is easy to be implemented in the
calculations of stellar evolution with ignorable extra time cost. We have
tested the linear model in stellar evolution, and have found that the linear
model can well reproduce the turbulent kinetic energy profile of full TCM, as
well as the diffusion coefficient, abundance profile and the stellar
evolutionary tracks. We have also studied the effects of different values of
the model parameters and have found that the effect due to the modification of
temperature gradient in the overshoot region is slight.Comment: 20 pages, 10 figures, accepted for publication in Ap
Automorphisms of K3 surfaces
In this note, we report some progress we made recently on the automorphisms
groups of K3 surfaces. A short and straightforward proof of the impossibility
of Z/(60) acting purely non-symplectically on a K3 surface, is also given, by
using Lefschetz fixed point formula for vector bundles.Comment: submitted to Proc. Conf. for 10th anniversary of Math. Inst. East
China Normal U. Contemporary Math. Amer. Math. So
The solar abundance problem: the effect of the turbulent kinetic flux on the solar envelope model
Recent 3D-simulations have shown that the turbulent kinetic flux (TKF) is
significant. We discuss the effects of TKF on the size of convection zone and
find that the TKF may help to solve the solar abundance problem. The solar
abundance problem is that, with new abundances, the solar convection zone
depth, sound speed in the radiative interior, the helium abundance and density
in the convective envelope are not in agreement with helioseismic inversions.
We have done Monte Carlo simulations on solar convective envelope models with
different profile of TKF to test the effects. The solar abundance problem is
revealed in the standard solar convective envelope model with AGSS09
composition, which shows significant differences (\rm{\sim 10 %}) on density
from the helioseicmic inversions, but the differences in the model with old
composition GN93 is small (\rm{\sim 0.5 %}). In the testing models with
different imposed TKF, it is found that the density profile is sensitive to the
value of TKF at the base of convective envelope and insensitive to the
structure of TKF in the convection zone. Required value of turbulent kinetic
luminosity at the base is about \rm{-13%\sim-19%L_{\odot}}. Comparing with
the 3D-simulations, this value is plausible. This study is for the solar
convective envelope only. The evolutionary solar models with TKF are required
for investigating its effects on the solar interior structure below the
convection zone and the whole solar abundance problem, but the profile of TKF
in the overshoot region is needed.Comment: 5 pages, 2 figures, accepted for publication in the ApJ Letter
Constraints on the size of the quark gluon plasma
We use simple entropy arguments to estimate the possible size of the QGP at
the AGS and the SPS. We find that the possibility to form a large volume of QGP
at the AGS or the SPS is very small. The size of the QGP at RHIC and the LHC is
also predicted.Comment: new references of finite size effects on the observables are adde
Multi-pion Bose-Einstein correlations in high energy heavy-ion collisions
Multi-pion correlations and wavepacket size effects on the pion multiplicity
distribution, pion momentum distribution and two-pion interferometry are
studied. It is shown that multi-pion Bose-Einstein correlations and the
wavepacket size cause an abundance of pions at low momentum, increase the mean
pion multiplicity and decrease both the apparent radius of the source and the
coherent source parameter derived from two-pion interferometry.Comment: 9 pages, 7 figure
Testing the core overshooting mixing described by the turbulent convection model on the eclipsing binary star HY Vir
Helioseismic investigation has suggested to apply the turbulent convection
models (TCMs) to the convective overshooting. Using the turbulent velocity in
the overshooting region determined by the TCM, one can deal with the
overshooting mixing as a diffusion process, which leads to incomplete mixing.
It has been found that this treatment can improve the solar sound speed and the
Li depletion in open clusters. In order to investigate whether the TCM can be
applied to the overshooting mixing outside the stellar convective core, new
observations of the eclipsing binary star HY Vir are adopted to calibrate the
overshooting mixing parameter. The main conclusions are as follows: (i) the TCM
parameters and the overshooting mixing parameter in the solar case are also
suitable for the eclipsing binary system HY Vir; (ii) the incomplete mixing
results in a continuous profile of the hydrogen abundance; (iii) the e-folding
length of the region, in which the hydrogen abundance changes due to the
overshooting mixing, increases during the stellar evolution.Comment: 9 pages, 7 figures, ApJ accepte
Multipion symmetrization effects on the source distribution
Any-order pion interferometry formulas for fixed pion multiplicity events and
for mixed events are given. Multipion Bose-Einstein correlation effects on the
two-pion interferometry and source distribution are studied. It is shown that
generalized pion interferometry formula should depneds on pion multiplicity
distribution. Pion condensate is also discussed in the paper.Comment: invited Talk given at the 8-th international workshop on
multiparticle production(correlation and fluctuation'98), June 14-21, 1998
Hungary. To be published in the proccedin
Quotients of K3 Surfaces Modulo Involutions
Let X be a K3 surface with an involution g which has non-empty fixed locus
X^g and acts non-trivially on a non-zero holomorphic 2-form. We shall construct
all such pairs (X, g) in a canonical way, from some better known double
coverings of log del Pezzo surfaces of index at most 2 or rational elliptic
surfaces, and construct the only family of each of the three extremal cases
where X^g contains 10 (maximum possible) curves. We also classify rational log
Enriques surfaces of index 2. Our approach is more geometrical rather than
lattice-theoretical (see Nikulin's paper for the latter approach).Comment: 30 pages. Japanese J. Mathematics, to appea
Convective overshoot mixing in stellar interior models
The convective overshoot mixing plays an important role in stellar structure
and evolution. However, the overshoot mixing is a long standing problem. The
uncertainty of the overshoot mixing is one of the most uncertain factors in
stellar physics. As it is well known, the convective and overshoot mixing is
determined by the radial chemical component flux. In this paper, a local model
of the radial chemical component flux is established based on the hydrodynamic
equations and some model assumptions. The model is tested in stellar models.
The main conclusions are as follows. (i) The local model shows that the
convective and overshoot mixing could be regarded as a diffusion process, and
the diffusion coefficient for different chemical element is the same. However,
if the non-local terms, i.e., the turbulent convective transport of radial
chemical component flux, are taken into account, the diffusion coefficient for
each chemical element should be in general different. (ii) The diffusion
coefficient of convective / overshoot mixing shows different behaviors in
convection zone and in overshoot region because the characteristic length scale
of the mixing is large in the convection zone and small in the overshoot
region. The overshoot mixing should be regarded as a weak mixing process. (iii)
The result of the diffusion coefficient of mixing is tested in stellar models.
It is found that a single choice of our central mixing parameter leads to
consistent results for a solar convective envelope model as well as for core
convection models of stars with mass from 2M to 10M.Comment: 9 pages, 2 figures, accepted for publication in ApJ
- …