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1.
The effect of a uniform magnetic field on the envelope convection zone of an 8.8M
star has been studied. The adiabatic exponents
i
(i=1, 2, 3), adiabatic temperature gradient and specific heat of stellar matter has been computed. It is shown that the magnetic field tends to increase the values of adiabatic temperature gradient and specific heats of stellar matter in the envelope convection zone. 相似文献
2.
In this paper the gravitational collapse of cosmic gas clouds and formation of star clusters has been considered. Hoyle's view of successive fragmentation has been taken as the basic mechanim in the present work. The initial masses of protostars have been estimated as the function of their distances from the centre of the cluster and the intensity of the magnetic field of the medium. It has been shown that the fragmentation process is greatly inhibited by the presence of a strong magnetic field. A model has been constructed showing how a protostar grows in mass by accretion from the surrounding medium, on the basis of the assumption that as the star moves at random in the cluster it picks up a fraction of the material through which it passes. It has been estimated that a protostar of initial mass of about 0.1M
grows to one of 1.0M
in a time period which ranges from a few multiples of 105 to a few multiples of 107 yr, depending on the parameters involved in the accretion process. The number of stars per unit mass range has also been estimated; it is found to be proportional tom
–3.3,m being the mass of the star. 相似文献
3.
A new series of neutron star models has been computed. The equation of state used included the effects of nuclear dissolution, nuclear forces, and the presence of hyperons. The nuclear forces were introduced through use of a generalized form of the Levinger-SimmonsV
andV
potentials. The maximum stable masses obtained were 2.28 and 2.37M
, respectively. Details are given of the structure of the outer layers which are expected to be crystalline. Expressions are given for the angular momentum and rotational energy of a neutron star and the relevant moment of inertia is tabulated for the models. 相似文献
4.
A. Kovetz 《Astrophysics and Space Science》1970,6(2):293-296
It has been recently established that there exists a maximal red shiftz
max for a homogeneous star of given massM. The relationshipz
max(M) is obtained for neutron stars in the mass range 0.71M/M
12.06. 相似文献
5.
A model of a first generation intermediate star of 5M
, with Z=0 has been considered. The model is at an advanced stage of its evolution and has a double shell burning. It burns helium in the inner shell, and hydrogen, via CNO cycle, in the outer shell.
=(log/log)
T
and
T
=(log/logT)
were computed allowing for the oscillations of the relative mass abundance of the reagents in nuclear reactions. Including
=(log/log)
T
and
=(log/logT)
of mean molecular weight and the effect of the oscillations of abundances due to nuclear reactions, stability was studied. Contrary to the results of the static calculations, we found that instability due to the excitation mechanism provided by the high temperature sensitivity of energy generation rate propagates up to the surface. Thus the model in question was found to be unstable against radial adiabatic pulsations, in its fundamental mode. 相似文献
6.
A study of pulsational properties with evolution has been done for a 15.6M
star withX
e
=0.90 andY
e
=0.08. Pulsational properties in the hydrogen-burning stages have been compared with those in helium-burning stages. A comparison with observed characteristics of Cepheids, classical Cepheids and supergiant variables has been made during the course of its evolution. In addition, models of 5,9 and 15M
withX
e
=0.708,Y
e
=0.272 have also been studied for pulsational properties during the helium burning stage. It is also seen that pulsational instability is sensitive to changes in initial chemical composition and opacity parameters,n ands. A low helium abundance could be a reason for the stability of the models, even when lying in the instability strip of the H-R diagram. 相似文献
7.
Dilhan Ezer 《Astrophysics and Space Science》1972,18(1):226-245
The evolution of a first-generation 3M
star from the threshold of stability through the stage of helium exhaustion in the core has been studied. The total time elapsed is 4.174×108 yr and most of this time is spent in the blue-giant region of theH-R diagram. Hydrogen-burning near the Main Sequence occurs at a high central temperature via the proton-proton chain until the triplealpha reactions generate a small amount of C12 toward the end of the hydrogen-burning phase. The corresponding evolution time is longer than that of a normal population I star with the same mass. The ignition of the triple-alpha processes begins in a mildly degenerate, small convective core while the star still has a high surface temperature. Helium-burning in the core, coupled with hydrogenburning in the shell, occupies a period of about 1.8×107 yr, which is only one-third that of a normal star. The mass of the star interior to the hydrogen shell source has increased to a value of 0.50M
near the end of core helium exhaustion. This region maintains an inhomogenous composition composed of helium, carbon and oxygen. 相似文献
8.
We can define some adiabatic exponents for neutron star cores. The equality of and 3 leads to an equation of stateE=P ln(K/P) orP=K exp(–E/P). This equation has been solved alongwith equations for hydrostatic equilibrium for different physical conditions at the centre. The parameters of isothermal neutron star cores have been computed by taking surface densityE
a=2×1014 g cm–3. ForP
0=E
0 the maximum mass and radius of neutron star core are 3.25M
and 17.14 km, respectively. 相似文献
9.
P. R. Amnuel O. H. Guseinov H. I. Novruzova Yu. S. Rustamov 《Astrophysics and Space Science》1985,113(1):59-81
On the basis of data on planetary nebula (PN) central star temperatures obtained by measurements in the ultraviolet (UV) range, the empirical calibration dependence between the number of Lyman photons emitted by a central starS and PN diameterD, is constructed. The temperatures of 118 PN central stars are estimated with this dependence. It is shown that the central star masses are distributed in a wide interval from 0.5 to 1.2M
. About 60% of all stars have masses <0.6M
, about 25% have masses >0.6M
and the remainder have masses 0.6M
. The averaged empirical tracks of evolution of low-mass (<0.6M
) and massive (>0.6M
) central stars differing considerably from each other are constructed. It is shown that the majority of central stars may possess hot chromospheres (T>2×105 K) which spread for several tens of radii of the central star. The PN originates as a result of ionization of the matter ejected by a red giant at the superwind stage. The cause for this ionization is the UV radiation of the PN central star. 相似文献
10.
Jan Palouš 《Astrophysics and Space Science》1986,128(1):151-156
The relation between molecular clouds, star clusters, and the stellar component of the galactic disk is investigated. According to Elmegreen (1985) bound stellar systems, e.g., open star clusters, can be formed from molecular cloud of mass 104
M
. A close encounter with a giant molecular cloud or massive black hole disrupts such stellar systems and forms superclusters. This explains why some open star clusters are so mass-deficient. Unbound stellar systems, e.g., expanding OB associations, are formed from molecular clouds of mass 105
M
. When disruptive O-type stars appear the star formation is halted and the cloud is destroyed. An example of the relict of GMC disruption in the solar vicinity is Gould's belt. The velocity dispersion-versus-age relation is also investigated and explained as a consequence of gravitational scattering of stars on GMC, or massive black holes, or as due to recurrent transient spirals.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986. 相似文献
11.
J. Perdang 《Astrophysics and Space Science》1982,83(1-2):311-333
We show that the overall densityg() of asymptotic acoustic frequencies of a star obeys a Weyl lawg()
D–1, whereD is the dimensionality of the oscillating stellar configuration. For realistic stars with a finite non-zero surface sound speed,D is equal to the actual dimensionality of the star,D=3. For formal models with a vanishing sound velocity at the surface, heuristic arguments lead to a dimensionality parameterD=4.5. The empirical frequencies of Eddington's standard model are found to be consistent with the latter distribution, with reasonable agreement already occurring in the low-frequency range >
i
2× fundamental radial mode. We argue that real stars obey this 3.5-power law in some finite frequency interval
i
<<
f
,
f
being a very high frequency critically depending on the surface sound velocity, while the full asymptotic law, withD=3, holds for >
f
. 相似文献
12.
Shiv S. Kumar 《Astrophysics and Space Science》1972,16(1):52-54
Arguments are presented to show that Jupiter could not have been formed as a star of mass 0.001M
and that the observed excess energy is not due to gravitational contraction from an extended, gaseous state. 相似文献
13.
If the assumption of a catastrophic explosion during the formation of a neutron star is correct, the parent systems for klovsky's model of SCO XR-1 seem to have been very short-period white-dwarf binaries. A white dwarf originally in contact with its Roche limit is forced to lose mass. During the ejection of matter the primary may pass the white-dwarf mass limit and become a neutron star. The mass transfer time-scale can change from pulsational to thermal, and a mass flow of 10–9
M
per year needed for SCO XR-1 can be understood, while at the same time the orbital period will increase. 相似文献
14.
The adiabatic theory of interaction between high and low frequency waves has been studied for the case of electron plasma oscillations and ion acoustic waves and the results are applied to the solar wind. The modified dispersion relation for ion acoustic waves has been derived, taking a Gaussian distribution for plasmons. Two limiting cases of the spectrum are studied. For a broad spectrum, the plasma turbulence has a destabilising effect by introducing a growth rate denoted by turbulence, which is positive for k
0 > (m
e/
m
i
)1/2
De
–1
, k
0 being the central wave numger of the spectrum,
De the electron Debye length. Also, even for v
d(drift velocity between electrons and ions) < c
s, we arrive at unstable ion acoustic modes. For narrow spectrum, the plasma turbulence has a stabilising effect. 相似文献
15.
Gang Zhao Yonggheng Zhao Jtasheng Huang Lonlong Feng Keliang Huang Qiuhe Peng Tan Lu 《Astrophysics and Space Science》1988,141(1):169-176
In this paper, the neutrino mass has been determined from SN1987a observation in a manner that the simultaneity of neutrino emission is not regarded as the starting point, but is itself defined through the analysis by Monte-Carlo simulation. The result is that the neutrino mass lies in 3–4 eV, possiblym
v
3.6 eV. Neutrino luminosity variation and neutrino spectrum are also obtained. Comparison with theories gives further support to the mass determination, and also predicts the mass of progenitor star of SN1987a to be in the range of 12–25M
.The project supported by the National Natural Science Foundation of China. 相似文献
16.
In this work an exhaustive study of static massive configurations with a constant local adiabatic exponent (1) has been made under various physical conditions at the centre. The static parameters of these structures have been calculated at the extreme causality condition. These structures have been used to model neutron stars and the various neutron star parameters have been calculated. The radial pulsation and rotation of these configurations have also been discussed. 相似文献
17.
We give the results of photographic, photoelectric, and spectral observations of the flare star PP Ori. The 109 photographic observations used, which were obtained on the 40 Schmidt telescope of the Byurakan Observatory over a period of about 20 years, and four spectra obtained on the same telescope with a4° objective prism show no variation in brightness. Photoelectric observations in the UBVR bands using the 50cm and 60cm telescopes of the high-altitude Maidanak station of the Tashkent Astronomical Institute in 1987 and 1989 give grounds for suspecting a variation in brightness much larger than observational errors. Spectral observations of the star PP Ori made on the 2.6m telescope of the Byurakan Observatory show weak H emission. The results of all these observations show that PP Ori is an Orion variable of spectral class K7-M0 with absolute visual magnitude7
m
5–8
m
5.Translated fromAstrofizika, Vol. 38, No. 2, 1995. 相似文献
18.
Halil Kirbiyik 《Astrophysics and Space Science》1989,153(2):289-296
A model of first-generation intermediate mass star of 5M
with no metals has been considered. The vibrational instability of this model has been investigated. The model, in question, burns helium in the core. Calculations have been performed for the first and second harmonics as well as for the fundamental mode. The model has been found to be vibrationally stable toward radial pulsations. 相似文献
19.
E. Lohinger C. Froeschlé R. Dvorak 《Celestial Mechanics and Dynamical Astronomy》1993,56(1-2):315-322
The Lyapunov characteristic numbers (LCNs) which are defined as the mean value of the distribution of the local variations of the tangent vectors to the flow (=ln
k
i
) (see Froeschlé, 1984) have been found to be sensitive indicators of stochasticity. So we computed the distribution of these local variations and determined the moments of higher order for the integrable and stochastic regions in a binary star system with =0.5. 相似文献
20.
P. Bouwman 《Astrophysics and Space Science》1980,68(2):525-531
On the assumption that, at the moment of the supernova explosion, the presently nondegenerate companion of Her X-1 was a Main-Sequence star with polytropic indexn=3, it is found that the effects of impact and ablation cannot have removed more than about 10% of its pre-supernova mass. A remnant mass for a neutron star of 1.4M
was adopted. The effects of impact and ablation were calculated in the manner given by Wheeleret al. (1975). Depending on the ejection velocity of the SN shell, it is found that with a pre-SN mass of 2.2M
(i.e., the maximum possible value) for the non-degenerate component, the initial binary period was in the range 2–4 days. 相似文献