A possible model of supernovae: Detonation of12C

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)].     

The effect of convection on the process of carbon burning in a degenerate core

The results of a numerical investigation of the hydrostatic carbon burning in a degenerate carbon core withM=1.4M are presented. Convective heat transfer has been taken into account according to the mixing length formalism. It is shown that for small convection the effective (10^–3) computational results are in agreement with the assumption of a hydrostatic evolution of the core. At 10^–2 the burning times in successive mass zones become less than the hydrodynamic time for the core. In this case carbon burning starts with a rapidly propagating thermal instability. The connection between the convective and neutrino mechanisms of burning propagation is discussed.     

Hidden mass in the solar neighborhood

It is suggested that the minimum mass of a star at the time of its formation is approximately 0.01M . Making use of this fact and the stellar mass functionF(M) M ^–, it is found that the hidden mass (or the missing mass) in the solar neighborhood may be explained by the presence of a large number of invisible stars of very low mass (0.01M M<0.07M ).     

Hollow beam distribution of energetic electrons and higher harmonics of electron cyclotron maser

The variations of the growth rates of ECM at first four harmonics in X-, Z-, and O-modes excited by a hollow beam distribution of weakly relativistic electrons with a parameter _p / _e are presented in this paper. The results show that the second harmonic of ECM in X-mode dominates the instability if < 1, and if 1.2 , 2 or 2.2 3 the third or fourth harmonic will dominate. The second and third harmonics of Z-mode waves grow faster only if 2 2.2 and 3 3.2, respectively, so it would not be a competition in most cases. It is suggested that the ECM emission at these harmonics in X-mode is a possible mechanism to produce solar spike emissions with high brightness temperature at shorter and longer decimetric wavelengths.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985.On leave from the Department of Astronomy, Nanjing University, Nanjing, The People's Republic of China.     

Pulsars: Observational parameters and a discussion on dispersion measures

The relevant data for the known 147 pulsars are presented in graphical and tabular forms. Various data correlations are discussed, and a detailed analysis of pulsar dispersion measures and distances is given. The range of the electron densities in the diffuse interstellar medium is found to be 0.01 cm^–3n _e0.1 cm^–3, and n _e0.03 cm^–3. The dispersion scale height for pulsars is found to be 5.9±0.7 pc cm^–3 implying a linear scale height of 200 pc, which is much smaller than the electron scale height of our Galaxy.Astrophysics and Space Science Review Paper.     

Composition and adiabatic index of matter at high temperatures

The equation of state and the adiabatic index of thermally dissociated matter composed of nucleons, electrons, positrons, neutrinos, antineutrinos and photons are calculated in the density and temperature ranges, 10⁹q(g cm^–3)10¹³, 2×10¹⁰T K5×10¹¹, respectively. The interaction between nucleons is explicitly included. This leads to a softening of the equation of state. The implications of the results for the problem of supernova collapse are discussed.     

The peculiarities of diffusion of the galactic cosmic rays at low energies

I give an interpretation of a result of Simpsonet al. (1988) on the variation with kinetic energyT _i of the mean pathlengthX _m (T _i ) of the galactic cosmic rays (CGRs) in the range 0.1T _i 10.0 GeV nucl^–1. I argue that the data onX _m (T _i ) may be interpreted in terms of a model of GCR diffusion on the one-dimensional Alfvén-wave turbulence, having a cutoff in the spectrum at frequencies _h , where _h is the proton gyrofrequency. The cutoff results in changing of the character of variation of the GCR diffusion coefficientD(T _i )T ^a in the rangeT _i 1 GeV nucl^–1 towards some more complicated variation at 0.1T _i 1.0 GeV nucl^–1 due to the peculiarities of the pitch-angle scattering at 90⁰.     

Diffuse galactic FUV radiation and interstellar dust grains

A re-analysis of the diffuse far UV radiation ( 1350–1480 Å) observed in the sky region ofl ^II180° and 0°b ^II40° is presented, as a revised version of a paper by Hayakawaet al. (1969). In comparison with the previous one, the value of the half optical depth of the Galazxy in our wavelength region is reduced, and the values of the albedo coefficient and the forward phase functiong are not well determined. If, however, we combine our results with the theoretical model of interstellar grains by Gilra, the value of is given by 0.13(5)0.18(5).     

Charged particle thermonuclear reactions in nucleosynthesis

Thermonuclear reaction rates are calculated at temperatures consistent with nucleosynthesis conditions in stars and supernovae (10⁹T10¹⁰ K). The cross sections as a function of energy are determined by averaging over a density of compound nuclear states, an individual resonance contribution being represented by the Breit-Wigner formula. The proton and -particle channel radii are estimated by fitting experimental (p, n) and (, n) cross sections for nuclei in the mass range 40A200. The influence of the diffuseness of the nuclear surface on barrier penetration is taken into account by multiplying the square well penetration factors by a reflection factor in the manner described by Vogtet al. (1965). Thermonuclear rates calculated by these procedures are compared with sums over experimentally determined resonance strengths for a number of charged-particle reactions involving medium mass nuclei (24A40).     

Noise-Storm Continua: Power Estimates for Electron Acceleration

We use a generic stochastic acceleration formalism to examine the power L_in (erg s^-1) input to non-thermal electrons that cause noise-storm continuum emission. The analytical approach includes the derivation of the Greens function for a general second-order Fermi process, and its application to obtain the particular solution for the non-thermal electron distribution resulting from the acceleration of a Maxwellian source in the corona. We compare L_in with the power L_out observed in noise-storm radiation. Using typical values for the various parameters, we find that L_in 10²³–10²⁶ erg s^-1, yielding an efficiency estimate L_out/L_in in the range 10^-10 10^-6 for this non-thermal acceleration/radiation process. These results reflect the efficiency of the overall process, starting from electron acceleration and culminating in the observed noise-storm emission.     

Gamma-ray bursts from high velocity neutron stars

We investigate the viability of the Galactic corona model of -ray bursts by calculating the spatial distribution of neutron stars born with high velocities in the Galactic disk, and comparing the resulting brightness and angular distribution with the BATSE data. We find that the Galactic corona model can reproduce the BATSE peak flux and angular distribution data for neutron star kick velocities 800 km s^–1, source turn-on ages 10 Myrs, and sampling depths 100 kpc d _max 400 kpc.     

The proton-proton reaction and related reactions in an intense magnetic field

The reaction rates for the proton-proton reaction and the related electron capture reaction in a strongly magnetized relativistic electron gas of arbitrary degree of degeneracy are computed. The proton-proton reaction rates are unaffected by the presence of the magnetic field for field strengths up to the critical valueH _q =m ² c ³/e=4.414×10¹³G. For fields greater thanH _q , the proton-proton reaction rates are enhanced linearly with (=H/H _q ).The PeP reaction is investigated in detail for a wide range of temperatures, densities and magnetic field strengths that are of interest. The main results are as follows: In the non-degenerate regime the reaction rates are significantly reduced for high temperatures (T ₉5) and low fields (1). For instance, _pep(H)=0.04 _pep(O) at =10^–3,T ₉=10. For relatively high fields (>1) and low temperatures (T ₉2), the reaction rates are enhanced approximately linearly with . In the complete degenerate regime the reaction rates are reduced up to one-third of the field-free value for moderate densities (₆/_e10). At high densities (₆/_e10) the reaction rates are unaffected by the magnetic field.     

Radio source orientation and the cosmological interpretation of the angular size-redshift relation for double-lobed quasars

The angular size-redshift test for quasars was compared with various cosmological models including non standard models. The possible effects of radio source orientation and relativistic beaming were taken into account in the analysis.It was found that orientation effects alone were not sufficient to explain the observed-z relation in terms of Friedmann models. In addition, linear size evolution of the formD ~ (1 +z)^–n , with 0.75 n 1.2 would be required for 0 1.0, or possibly an inverse correlation between luminosity and linear size. The non-standard cosmological models all gave better fits to the deprojected data than the Friedmann models in the absence of evolutionary effects, with the tired light effect providing the best fit.     

Seismic Diagnostics on Stellar Convection Treatment from Oscillation Amplitudes of p-modes

The excitation rate P of solar p-modes is computed with a model of stochastic excitation which involves constraints on the averaged properties of the solar turbulence. These constraints are obtained from a 3D simulation. Resulting values for P are found 4.5 times larger than when the calculation assumes properties of turbulent convection which are derived from an 1D solar model based on Gough (1977)'s formulation of the mixing-length theory (GMLT). This difference is mainly due to the assumed values for the mean anisotropy of the velocity field in each case.Calculations based on 3D constraints bring the P maximum closer to the observational one.We also compute P for several models of intermediate mass stars (1 M 2 M).Differences in the values of P _max between models computed with the classical mixing-length theory and GMLT models are found large enough for main sequence stars to suggest that measurements of P in this mass range will be able to discriminate between different models of turbulent convection.     

Pulsar radio emission from expanding charge sheets

We semi-quantitatively calculate the distribution of energy in frequency and angle emitted from a sheet of charges that are moving out relativistically along dipolar magnetic field lines originating near the magnetic polar caps of a rotating neutron star. The angular distribution is conical with the angle of maximum intensity varying with frequency as ^–1/4 for _c 2 _c /(R _M ²), whereR_M is the initial angular radius of the charge sheet at the surface of the star of radiusR. At higher frequencies the width of the angular cone remains constant. The radiation is linearly polarized with the polarization vector in the plane of the line of sight and the magnetic axis. A sheet of uniform charge density and finite thickness has a frequency spectrum that varies from ^–3/2 to ^–4 for _c and _c , respectively. These features are in good general agreement with the observed characteristics of the intensity, pulse shape, and frequency spectrum of the radio pulses from pulsars.Operated by Associated Universities, Inc., under contract with the National Science Foundation.     

Neutrino luminosity by the ordinary URCA process in an intense magnetic field

The neutrino luminosity by the ordinary URCA process in a strongly magnetized electron gas is computed. General formulae are presented for the URCA energy loss rates for an arbitrary degree of degeneracy. Analytic expressions are derived for a completely degenerate, relativistic electron plasma in the special case of neutron-proton conversion. Numerical results are given for more general cases.The main results are as follows: the URCA energy loss rates are drastically reduced for the regime of great degeneracy by a factor up to 10^–3 for 1, andT ₉10, where =H/H _q ,H _q =m ² c ³/eh=4.414×10¹³ G. In the non-degenerate regime the neutrino luminosity is enhanced approximately linearly with for the temperature range 1T ₉10. Possible applications to white dwarfs and neutron stars are briefly discussed.We have been recently informed that in Gamow home-dialect (Odessa dialect) URCA means thief — (Private communication from Prof. G. Wataghin).     

Emden-chandrasekhar axisymmetric,rigidly rotating polytropes

An approximate analytical method of solving the polytropic equilibrium equations, first developed by Seidov and Kuzakhmedov (1978), has been extended and generalized to equilibrium configurations of axisymmetric systems in rigid rotation, with polytropic index,n =n _p + _n , nearn _p =0, 1, and 5. Though the details of the method depend on the value ofn _p , acceptable results are obtained for | _n | 0.5 to describe slowly rotating configurations in the range 0n1.5, 4.5n5. In the limit of rotational equilibrium configurations, when the distorsion may be large enough, a satisfactory approximation holds only in the range 0n, 1n1.5, 4.5n5.     

The interrelationship between cosmic dust and the microwave background

Attention is given to the radiation of microwaves by charged dust in space. Presently-used particle distributions do not restrict the presence in space of large numbers of small (r<10^–6 cm) silicate grains, but it is shown that such densities (10^–25–10^–26 g cm^–3) of small grains would produce a microwave background with an energy density of the same order of magnitude as the energy density of the (presumed) cosmological 3 K background. Limits set by the isotropy of the latter are: (HI clouds)10^–26, (Galactic plane)10^–30, (Halo)10^–32, (Local Group)10^–34 g cm^–3. These limits imply that either there is a cutoff in particle distributions atr10^–6 cm, or that the density of silicate grains in space has been generally overestimated, or that cosmic rays have broken up a lot of grains so that they now form a population of grains of very small size (10^–7 cm) which are difficult to detect by conventional methods. One way to look for the latter population is by studying expected distortions of the 3 K spectrum to the short wavelength side of the portion hitherto observed (grains may have a size distribution able to give an approximate black-body curve for radiation from larger grains of 10^–6 cm size), and by testing the effective energy density of the 3 K field in other galaxies.     

On the mass and distance of the Quasi-Stellar Object 3C 273

For the QSO 3C 273 we derive, on the basis of two different theoretical models, expressions for a lower limit to the mass of the QSO, as a function of its distance. We conclude that an appreciable gravitational redshift component is consistent with the observational data only if the QSO mass is at least Galactic in magnitude. The setting of an independent upper limit to the QSO massM10¹⁰ M could indicate that the QSO redshift is predominantly cosmological in nature.     

On the relative roles of unipolar and mixed-polarity fields

Away from plages, solar magnetic fields may be classified as unipolar or as of mixed polarity, though the distinction is strictly arbitrary. The dividing line used here is 0.4 ¦B _minor/B _major¦ 1, where average fields of major and minor polarities are measured over large areas. Some of their statistical properties and cyclical variations are detailed. In unipolar regions, 3 B _major 50 G, B _minor 0.1 B _major, and ¦B¦ 1.1 B _major. In regions of mixed polarity, 3.5 ¦B¦ 10 G.Below latitudes of ± 60°, mixed polarities predominate for about 5 yr around sunspot minimum. For several years around sunspot maximum, unipolar fields fill the 20°–40° zone completely, and occupy about 75% of the 0°–20° and 40°–60° zones.The polar unipolar fields are weak on the whole (Bmajor 4 G for 6 typical days in 1976–79), with small regions having stronger fields at times, probably not exceeding B _major = 10 G. Again B _minor 0.1 B _major. There is no direct way at present of measuring properties of polar mixed fields, such as may occur around sunspot maximum, but by inference ¦B¦ 2 to 5 G.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.