首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 701 毫秒
1.
A non-LTE study of the Type IIb supernova 1993J in the galaxy M81 taking into account nonthermal ionization and line blocking effects is carried out. Hydrodynamical models and theoretical spectra clearly show that nonthermal ionization and excitation dominate after the second maximum, at day 30, and play a decisive role in reproducing both the smooth tail of the light curve and the emergence of helium lines in the spectrum, similar to those observed. Based on our model of supernova 1993J, we predict that the light curves of Type Ib supernovae should be subject to nonthermal ionization and excitation at earlier times than even those for supernova 1993J. In our model, the outburst of supernova 1993J is interpreted as the explosion of a 4 M red supergiant, which underwent core collapse and left a neutron star in a binary system. The progenitor is supposed to have a helium core mass of 3 M, corresponding to a 13 M main-sequence star. Supernova 1993J adds evidence to the scenario that Type Ib supernovae originate from moderately massive stars on the main sequence that have lost their hydrogen envelopes in interacting binary systems.  相似文献   

2.
High resolution OVRO CO 1–0 observations of the inner 30 in the LINER galaxy NGC 5218 reveal the presence of a double centrally peaked molecular concentration with extensions out to a radius of 12. The molecular mass detected is 2.4 × 109 M and the gas surface density is high, 3000 M pc square in the inner 500 pc. The SFR is 2–3 M yr–1 and the SFE is 13, which are low or moderate values for that gas surface density. We interpret the inner feature as a rotating molecular ring with a radius of 200 pc. We furthermore suggest that the LINER activity in NGC 5218 is not caused by an aging starburst, but by a buried AGN.  相似文献   

3.
The innermost region of slim accretion disks with standard viscosity is unstable against axisymmetric radial inertial acoustic perturbations under certain conditions. Numerical simulations are performed in order to demonstrate behaviors of such unstable disks. It is shown that oscillations with the period of 10–3 (M BH/M ) s can be excited near the inner edge of the disks, whereM BH is the mass of the central object. This kind of unstable disks is a possible origin of the periodic X-ray time variabilities with period of 104s observed in a Seyfert galaxy NGC 6814.  相似文献   

4.
Galaxies may have formed by fragmentation in a collapsing cloud of very large mass. The most massive galaxies were formed from fragments which were nearly but not quite opaque: the least massive galaxies were formed from fragments about as large as the Jeans mass. If the maximum mass of galaxies is 1013 M , then the minimum mass should be 106 M .  相似文献   

5.
The structure and evolution of a slow reaction front propagation into a cool, hydrogen rich shell above an inert core has been studied. It has been found that, during the evolution of the front, the total radiative luminosity drops from 104 L to 10–4 L in a time scale of the order of 109 yr. The burned up fraction of the fuel is found to be less than 1%.  相似文献   

6.
We use a simple equation of state, in which the adiabatic index depends on opacity and ionization and we integrate the dynamical and thermodynamical equations for the gravitational collapse of a typical solar composition protocloud, up to the virialization of the energies. Following the evolution of the thermal energy and ionization fraction, violent bounces are obtained at the sudden hardening of the equation of state, when the material becomes ionized.We also suggest a mechanism to explain the onset of protostellar winds.We introduce radiation losses in the model, and integrate again the modified equations, studying the evolution of a 1.1M protocloud. The object's effective temperature stays in a confined small zone of the IR region throughout its fast (40 yr) evolution and its luminosity oscillates and decreases from 5000L to 500L . The radius starts from 35 AU and shrinks down to 140R , before a physical instability gives birth to a strong shock wave with consequent mass loss.  相似文献   

7.
Doyle  J.G.  Keenan  F.P.  Ryans  R.S.I.  Aggarwal  K.M.  Fludra  A. 《Solar physics》1999,188(1):73-80
Using new close-coupling excitation rates for the C-like ion Siix, density-diagnostic ratios based on Siix lines have been re-evaluated and applied to a sequence of CDS observations taken above a polar coronal hole. The derived electron densities are in excellent agreement with previous values of Neestimated from the N-like ion Siviii for another coronal hole. The confirmed trend is for a fall-off of one order of magnitude within the first 0.3 Rabove the limb. These densities are well fitted with an analytic formula for the density profile out to at least 8 R, by which stage the electron density has fallen to 4×103 cm–3, from 1.5×108 cm–3at 1.0 R.  相似文献   

8.
Andreev  V. E.  Efimov  A. I.  Samoznaev  L. N.  Chashei  I. V.  Bird  M. K. 《Solar physics》1997,176(2):387-402
A statistical study of Faraday rotation fluctuations (FRF) has been performed using polarization angle data of S-band (f = 2.3 GHz) radio spacecraft signals. The measurements were recorded during the recurring superior conjunctions of the Helios probes, during which the solar proximate point of the radio ray path reached heliocentric distances between 3 and 34 R. The most commonly found temporal FRF spectra are power laws with an average spectral index 1.5 over the frequency range from 1 mHz < v < 10 mHz. The FRF variance decreases with heliocentric distance, the falloff exponent being 8 for R < 6 R and 3 for distances 8 < R < 6 R < 16 R. The results are interpreted under the assumption that the FRF are produced by Alfvén waves propagating in the coronal plasma. For the applicable range of heliocentric distances it is shown that Alfvén waves are in a regime of free propagation and probably transfer much of their energy to the kinetic energy of the solar wind. The spatial power spectrum of magnetic field fluctuations is inferred to be strongly anisotropic, the irregularities extending along the background magnetic field with axial ratios of the order of 10.  相似文献   

9.
Jagdev Singh 《Solar physics》1985,95(2):253-262
The line and continuum intensities deduced from the multislit spectra of the (Fe X) coronal emission line taken at the 1980 eclipse are used to discuss the relative roles of radiative and collisional excitation mechanisms. It is shown that for R/R < 1.2, collisional excitation is the predominant mode. Collisional as well as radiative excitation is equally important for 1.2 < R/R < 1.4, whereas beyond 1.4 R radiative excitation becomes dominant. The line width measurements indicate that a large number of locations have half-widths around 1.3 Å. The maximum half-width is reached at 1.4 R with an average value of 1.6 Å.  相似文献   

10.
Stars of intermediate mass (4M M9M ) may ignite the12C+12C reaction explosively because of the high degree of electron degeneracy in their central regions. After the exhaustion of helium burning in the core of such stars, a helium-burning shell develops which is thermally unstable. Approximating this shell by suitable boundary conditions, the subsequent evolution of the core is examined quantitatively by standard techniques. An explosive instability due to ignition and detonation of12C+12C develops at a central density c 2 × 109. Subsequent hydrodynamic expansion is computed; final velocities of expansion up tov20 000 km/sec are found. The star is totally disrupted; no condensed remnant is left. Such an explosion may be a plausible model for a significant fraction of supernovae. Investigation of the relevant nuclear reaction network shows that the entire core (M core1.37M ) is processed through12C burning,16O burning and silicon burning. Significant amounts of56Ni are produced. This nucleosynthesis is critically sensitive to the exact central density at which the12C+12C reaction ignites; several factors which affect this critical density are discussed. A brief summary of other supernovae thories which have been expounded in detail is presented for comparison.Supported in part by the National Science Foundation [GP-9433, formerly GP-7976], [GP-9114], and the Office of Naval Research [Nonr-220(47)].  相似文献   

11.
We observed Faraday rotation of linearly polarized radio waves from the Crab Nebula (Tau A) at 4170 MHz during solar coronal occultations in June 1971–75. Mean amplitudes of the variations of position angle are larger in an active phase of the solar cycle than in a quiet phase. In occultations in 1971 and 1973, the position angle of the polarization varied oscillatory by 20–50 degrees due to local magnetic structures in the corona with a typical scale-length of about 0.5 R . In 1974, we observed a typical variation of position angle of polarization which is expected from a Y-shaped field configuration in coronal streamers.The Faraday rotation is enhanced when the line of sight to Tau A passes through strong coronal magnetic fields computed from magnetograph observations, while the rotation is suppressed when the line of sight passes through large coronal holes observed in X-rays. Short-time oscillation of the rotation angle observed in 1971 and 1973 suggests that neutral sheets in coronal streamers oscillate at a period of 3 hours with an amplitude of 1 R at a distance of 10 R from the Sun.  相似文献   

12.
The life-time of the star on AGB is approximately 6 × 104 yr. We divide it into front half and back half of AGB (including to optical Mira variable and OH/IR star) according to their evolution character. The observations show that the star has non-pulsation, but constant mass loss rate ( 5 × 10–7 M yr–1) on front half of AGB. Its circumstellar envelope is formed. When the star has pulsation on back half of AGB, its mass loss rate is relative with time, and increases gradually. In this time the star is on the stage of optical Mira variable. When the mass loss rate reaches the value of 3 × 10–6 M yr–1, the star evoluted from the stage of optical variable into the stage of radio bright OH/IR star. On the end of AGB the mass loss rate reaches 10–4 M yr–1. (Band and Habing 1983, Hermen and Habing 1985).  相似文献   

13.
RecentUBV photometry of the RS CVn binary CF Tuc is discussed and analysed. If we combine the results with previously published spectroscopy we find radii of 1.63R for the hotter (6000 K) and 3.11R for the cooler (4500 K) component; both stars having a mass of about 1.3M . The distance to the system is put at 86±15 pc.Though the photometric data is incomplete in the coverage of some regions out of the minima, there is no significant evidence of the wave-type distortions — a known hallmark of RS CVn stars — and the data can be modeled by a standard eclipsing binary system in which the statistical test of goodness-of-fit (2) produces quite acceptable values for reasonable estimates of observational accuracy (0.01 mag). We, therefore, have no need to postulate any additional photometric complications, and feel entitled to some confidence in the reliability of the derived parameter set.  相似文献   

14.
The final dynamical collapse of oxygen cores of 103 and 104 M which undergo the pair formation instability is computed. These cores are found to suffer complete collapse, presumably to form black holes, in contrast to cores of 100M which have previously been found to explode completely, leaving no remnant. These calculations represent a first attempt to ascertain the outcome of evolution over several decades of mass previously unexplored. The outcome may have some relevance to models of X-ray sources in globular clusters.  相似文献   

15.
In this paper we calculate the number of close binaries formed during the evolution process of a globular cluster core. The globular cluster core is assumed to contain a massive black hole at its center. We show that the central black hole can drive binaries formation in the core and the rate of binaries formation depends on the mass of the black hole at its center. When the massM of the black hole is between 102 M and 3×103 M , there will be a few binaries formed. When the mass of the black hole is 4×103 M M6×103 M , the number of binary star formation will suddenly increase with a jump to the maximum value 58. When the mass of the black hole is 7×103 M M9×103 M , the number of binary star will immediately decrease. Whether cluster X-ray is produced mainly by the central black hole or by binaries in the core depends on the mass of the central black hole. Therefore, two cases arise: namely, black hole accretion domination and binaries radiation domination. We do think that we cannot exclude the possibility of the existence of a central black hole even when binary radiation characteristics have been observed in globular cluster X-ray sources.  相似文献   

16.
We present near infrared maps of the planetary nebula IC 418 taken at 5 arc sec spatial resolution. These show an extremely compact source structure at 1.65 m, and very much broader and more elliptical emission distributions at 2.2 and 3.6 m. The possibility that the near infrared continuum derives from small grains with low thermal capacity is discussed, and synthetic spectra are derived. These indicate a very much slower variation of flux with wavelength than would be deduced for grains at unitary temperature, and imply a near infrared continuum which is significantly cooler than maximum grain temperatures. Fits to the spectrum of IC 418 suggest that peak grain temperatures may approachT p0103 K (for –2), for instance, compared to the observed colour temperature of 650 K.Finally, the relevant grains are required to be refractory and, given the large C/O ratio in this nebula, probably consist of graphite. Their mass is also required to be small, and is probably of order 2×10–7 M . This compares with the probable total mass for large dust grains of 10–4 M . Although they are both small and warm, such grains would be expected to persist over the lifetime of the nebula, and may also be responsible for various NIR band emission features.  相似文献   

17.
We have discussed, in general, the important physical parameters, likemaximum mass, radius, and the minimum rotation period of self-bound,causally consistent, and pulsationally stable neutron stars (Q-starmodels) by using a realistic stiff EOS (such that, the speed of sound,v P N, or nP=K(E-E a ) n, where K 1 and n =1/(1-2N);where P and E represent respectively, the pressure and theenergy-density, and E a is the value of E at the surface (r = a) of the configuration) within the two constraints imposed by: (i) The minimumrotation period, P rot, for the pulsar known to date corresponds to1.558 ms, and (ii) The maximum number density anywhere inside thestructure for the models described as Q-stars cannot exceed 1nucleon/fm3. By using the empirical formula given by Koranda,Stergioulas and Friedman (1997) (KSF-formula), and imposing constraint(i), we have obtained an upper bound of M max 7.76 M radius a 32.5 km, and the central energy-density around 2.17 ×1014 g cm-3 (for n =1.01). Constraint (ii) provides the minimumrotation period, P rot 0.489 ms for the maximum mass M max 2.4 M, and the central energy-density around 2.20 ×1015 g cm-3 (for n =1.01). The speed of sound at the centre ofthese models approaches 99% of the speed of light `c' (in thevacuum) and vanishes at the surface of the configuration together withpressure. If we relax the maximum Kepler frequency imposed by the fastestrotating pulsar known to date (constraint (i)), in view of certainobservational effects and theoretical evidences, and allow the present EOSto produce larger rotation rates than the 1.558 ms pulsar, the maximummass of the non-rotating model drops down to a value 7.2 M .The higher values of masses ( 7 M ) and radii (31-32 km) obtained in this study imply that these models may representthe massive compact objects like Cyg X-1, Cyg XR-1, LMC X-3, and otherswhich are known as black hole candidates (BHCs). This study also suggestthat the strongest contender for black hole at present might be recurrentnova V404 Cyg (mass estimate 8 -12 M ).  相似文献   

18.
The study of supernova (SN) models with slow energy pumping is continued. At maximum luminosity the main characteristics of a SN are shown to be independent of the initial structure of the model (Table I, Figure 1). However, they depend on the massM e of the envelope, and on the intensity of energy pumpingL , with an increase ofM e leading qualitatively to the same changes in the SN parameters as a decrease inL (Table I, Figures 2 and 3). A simple relationship connecting the important SN parameters is obtained (Equation (6)). From the inflection of the color indexB-V curve, the possibility of deriving the characteristic time of energy pumping with intensityL 1044 erg s–1 is pointed out. The comparison of the extragalactic type I SN observations with the results of calculations leads to the estimate ofM e 0.3–0.7M.An investigation of the galactic type I SN remnants is carried out (Table III). The estimate ofM e 0.2–0.3M is obtained for the remnants of supernovae SN 1006, SN 1572, and SN 1604. It completely fits the results for the extragalactic type I SNs. The total initial mass of SN 1604 presupernova was shown to be at least about 7M .It was established that the Crab nebula resulted from the outburst of a peculiar SN. The unique properties of such SNs, including SN 1054, are due to the low intensity of energy pumping (L 1042 erg s–1). The mass of the envelope of the Crab nebula is evaluated to beM e 0.7M . SN 1054 was shown to have m max v =–4 m . 0 at maximum luminosity.  相似文献   

19.
In this paper I present a new evolution model of QSOs luminosity. The model is based on edges distribution of apparent magnitude-redshift of QSOs. After the quasars were formed, the luminosities were increasing until they attained their maximum value atz=2+a, where –0.1a0.6, then the luminosities were decreasing. If the QSOs originate from superconducting cosmic string of same initial massM i 1012 M , the formation epochs are different, most of the quasars start atz cutoff5.6. The most luminous QSOs start at later epochz cutoff5.15. The present sky survey echniques may give us the possibility to see the formation of QSOs at apparent magnitudem V 22.5 by chance of 0.3%.  相似文献   

20.
We present an edge-on Keplerian disk model to explain the main component of the 12.2 and 6.7 GHz methanol maser emission detected toward NGC7538-IRS1N. The brightness distribution and spectrum of the line of bright masers are successfully modeled with high amplification of background radio continuum emission along velocity coherent paths through a maser disk. The bend seen in the position–velocity diagram is a characteristic signature of differentially rotating disks. For a central mass of 30M, suggested by other observations, our model fixes the masing disk to have inner and outer radii of 270 and 750 AU.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号