Showing papers in "Astrophysics and Space Science in 1972"

Accretion of matter by condensed objects

Abstract: The equations of motion for steady-state spherical symmetric flow of matter into or out of a condensed object (e.g. neutron stars, ‘black holes’, etc.) are displayed and solved for simple polytropic gases. It appears that infalling matter may be heated as hot as 1012K and that X-ray luminosities of the order of 1037 erg s−1 could result. The two fluid (electrons and ions separately) approach is also examined and it is shown that electrostatic fields of the order of 105 V m−1 are required near the surface of the object. Such fields are not strong enough to significantly modify the space-time metric.

Some results of the cooperative photometric observations of the UV Cet-type flare stars in the years 1967–71

Abstract: The list of the cooperative photometric observations of the UV Cet-type flare stars that have been organized during the years 1967 to 1971 by the Working Group on Flare Stars of the IAU Commission 27 is given. The completeness and reliability of the data obtained are evaluated by comparing simultaneous observations at different observatories. the statistical analysis of the UV Cet, YZ CMi, EV Lac and AD Leo flares observed in the B-band is carried out. The flare energy spectrum in the energy range where observational selection effects are small is found to be d lnv/d lnE B=−1.4 to −1.9,v is an occurrence of flares with radiation energy ofE B. The total flares' radiation is equal to 1.7%, 1.2%, 0.3% and 0.4% of the quiet radiation in the B-band of the stars listed, and the main part of this total radiation is due to the strongest flares. Distributions of flare rise times (t r) and of rates of flare absolute luminosity increase (d2 E B/dt r 2≡E r) are considered; these parameters of flare are independent statistically for all stars studied. Correlation coefficientsr (E B,t r) andr (E B,r(E B,E r)) are rather small except r (E B,t r)=0.86 for the AD Leo flares. Contradictory conclusions on temporal distribution of flares infered by different investigators are noted.

Paleontological evidence on the Earth's rotational history since early precambrian

Abstract: The daily growth layers arranged into seasonal and tidal patterns, present in calcified structures of many modern as well as fossil organisms, provide evidence on the length of lunar month and year in the geological past.

The Gravitational Field of Flat Galaxies

Abstract: A set of bi-orthogonal pairs of functions is derived which is especially suited for the calculation of the gravitational field of flat galaxies. The functions are Hankel tranforms of associated Laguerre functions, or ‘Hankel-Laguerre functions’. They can be calculated by means of recurrence relations, which are derived from a generating function. Numerical computations are most efficiently performed using a related set of Chebyshev type functions, which have more economic recurrence relations. The necessary algorithms for efficient calculation of the field are derived using the properties of Hankel-Laguerre functions. This field calculation, can be used for a relatively cheap and simple computer simulation of galaxies.

Galactic cosmic ray modulation from 1965-1970.

Abstract: Numerical solutions of the cosmic-ray equation of transport within the solar cavity and including the effects of diffusion, convection, and energy losses due to adiabatic deceleration, have been used to reproduce the modulation of galactic electrons, protons and helium nuclei observed during the period 1965–1970. Kinetic energies between 10 and 104 MeV/nucleon are considered. Computed and observed spectra (where data is available) are given for the years 1965, 1968, 1969 and 1970 together with the diffusion coefficients. These diffusion coefficients are assumed to be of separable form in rigidity and radial dependence, and are consistent with the available magneticfield power spectra. The force-field solutions are given for these diffusion coefficients and galactic spectra and compared with the numerical solutions. For each of the above years we have (i) determined the radial density gradients near Earth; (ii) found the mean energy losses suffered by galactic particles as they diffuse to the vicinity of the Earth's orbit; (iii) shown quantitatively the exclusion of low-energy galactic protons and helium nuclei from near Earth by convective effects; and (iv), for nuclei of a given energy near Earth, obtained their distribution in energy before entering the solar cavity. It is shown that the energy losses and convection lead to near-Earth nuclei spectra at kinetic energies ≤100 MeV/nucleon in which the differential intensity is proportional to the kinetic energy with little dependence on the form of the galactic spectrum. This dependence is in agreement with the observed spectra of all species of atomic nuclei and we argue that this provides strong observational evidence for the presence of energy losses in the propagation process; and for the exclusion of low energy galactic nuclei from near Earth.

Numerical Simulation of Jetstreams. II: The Two Dimensional Case

Abstract: The dynamics of jetstreams have been studied by following the evolution of a simulation particle population. The self-gravitational field of the stream has been neglected, the individual small bodies interacting through hard, partially inelastic collisions only, no fragmentation or accreaction taking place. The chosen collision model — the beta-model — is given by Equation (4). The collisions will quickly establish a Rayleigh distribution of both eccentricities and inclinations, the average amplitude of the oscillations associated with eccentricity being up by approximately a factor √2. The velocity distribution inside the stream is highly non-Maxwellian. If the collisions are sufficiently inelastic, the stream is focused, the individual orbits becoming more and more circular (for azimuthally symmetric streams) and ecliptic. In the opposite case the collisions destroy the stream configuration rapidly. The beta collisional model is unable to produce any radial focusing.

Paleocratering of the moon: review of post-apollo data*

Abstract: As a result of the dating of lunar samples, we are in a position to utilize the lunar surface as a recorder of environmental conditions in the Earth-Moon neighborhood in the past. Plots of crater density vs rock age at different lunar landing sites can be used to date unexplored lunar provinces. These plots also demonstrate evolution in the population of planetesimals that struck the Moon. Prior to 4.1 aeons ago, the cratering rate on the Moon was at least 103 times the present rate, and the rate declined with a half-life less than 8×107 yr. During the interval from 4.1 to 3.2 aeons ago, the number of planetesimals showed an exponential decay with a half-life about 3×108 yr, corresponding to sweep-up of particles from solar orbits somewhat similar to those of Apollo asteroids. A more nearly constant cratering rate applied in the last three aeons. These data indicate that the Moon displays at least the final stages of an ancient accretion process; they also set certain conditions on possible capture processes relating to the Moon's origin. Pre-Apollo expectations that the Moon would provide a ‘Rosetta Stone’ for interpreting solar system history and planet formation thus appear justified.

Roche potentials including radiation effects

Abstract: A modified Roche potential which incorporates the effects of radiation pressure due to one component of a binary system is mathematically explored. In some cases, the resulting potentials do not exhibit the familiar contact surfaces of the classical Roche potential. The concept of a contact surface, which has been fundamental to the investigations of close binary systems, must be used with discretion for close binaries in which one component is very luminous. A convenient criterion for the existence of a contact surface is given by (1-μ) ≃ 3δc 3/2 $$(1 - 2(\tfrac{2}{3})^4 \delta _c )$$ , (δc≪1) where μ is the mass of the very luminous star in terms of the system mass. For systems of given μ, no contact surface exists if δ is greater than δc where δ is the ratio of radiation pressure force to gravitational attraction. Furthermore, energy considerations of the modified Roche potential indicate that binary systems with δ < δc should have a greater tendency to form rings than those with δ < δc.

Nonlinear dissipation of Alfvén waves

Abstract: Alfven waves are generated easily in many cosmic plasmas, but they possess no linear damping mechanism since they are not compressive. The most prominent nonlinear damping occurs when one Alfven wave decays into another plus a slow magnetosonic wave, or two Alfven waves combine into one fast magnetosonic wave; the resulting magnetosonic waves can then be dissipated. The nonlinear coupling rates are presented, with special emphasis on the astrophysically important case of sound speed ≪Alfven speed. Streaming cosmic rays generate Alfven waves moving in the direction of streaming, but they reabsorb the backward moving waves then produced by wave decay. The possible steady states for this system of cosmic rays and Alfven waves turn out to be highly restricted.

On the spiral structure of our Galaxy

Abstract: It is shown in the present paper that properties of the spiral wave in the Galaxy are determined by the mass distribution of its flat subsystem rather than by the full mass distribution. Then it turns out that better agreement with the observed spiral pattern furnish the ‘long’ waves in contrast to the ‘short’ waves in the Linet al. (1969) theory. With the surface density σI=40M⊙ /ps2 which is taken in the first approximation as independent on the galacto-centric distance, and the pattern velocityΩp=23 km/s kps, the evaluated spiral pattern fits surprisingly well with the Weaver (1970) map of the HI-distribution in the Galaxy, and is in good agreement with the Kerr (1969) map. The inner Lindblad resonance occurs at 2 kps from the Galaxy center, where Weaver has placed the ring condensation of the gas, and the outer resonance lies close by 14 kps. At the outer resonance the nonlinear phenomena are expected, which lead to chaotization of the regular structure. This seems to be consistent with the Weaver (1970) and Kerr (1969) maps.

Hydrogen atom in intense magnetic field

Abstract: The structure of a hydrogen atom situated in an intense magnetic field is investigaged. Three approaches are employed. An elementary Bohr picture establishes a crucial magnetic field strength, H sub a approximately equal to 5 x 10 to the 9th G. Fields in excess of H sub a are intense in that they are able to modify the characteristic atomic scales of length and binding energy. A second approach solves the Schrodinger equation by a combination of variational methods and perturbation theory. It yields analytic expressions for the wave functions and energy eigenvalues. A third approach determines the energy eigenvalues by reducing the Schrodinger equation to a one-dimensional wave equation, which is then solved numerically. Energy eigenvalues are tabulated for field strengths of 2 x 10 to the 10th G and 2 x 10 to the 12th G. It is found that at 2 x 10 to the 12th G the lowest energy eigenvalue is changed from -13.6 to about -180 eV in agreement with previous variational computations.

Studies of the chemical composition of cosmic rays withZ=3 30 at high and low energies

Abstract: We have measured the chemical composition of cosmic rays withZ≥2 over an energy range from ∼100 MeV/nuc to >2 GeV/nuc using 2 new large area counter telescopes. One of these instruments was a 4 element dE/dx×E× Range telescope, the other a 4 element dE/dx×Cerenkov× ×Range telescope. Two balloon flights with these telescopes at Ft. Churchill in the summer of 1970 provided a total of nearly 1000 Fe nuclei with a charge resolution ranging from ∼0.10 charge unit at Carbon to ∼0.25 charge unit at Fe. A detailed charge spectrum is obtained at both high and low energies. Some important differences exist between the present results and those obtained earlier, due in part to the improved statistical accuracy and in part to the improved background rejection of the present data. In particular, the abundance of Cr and Mn are each found to be ∼0.10×Fe in contrast to the earlier ratio of ∼0.30 found by some workers for each of these nuclei. The abundance of these two nuclei, as well as others in the 15–25 range, shows no strong dependence on energy. We have extrapolated our composition data to the cosmic ray sources using a variety of interstellar path length distributions. The abundances ofall secondary nuclei withZ between 3–25 are consistent only with propagation models which have vacuum path length distributions which do not differ greatly from exponential. The source abundances of nuclei withZ=15, 17, 18, 19, 21, 22, 23, 24, and 25 are found to be <0.02×Fe. For the remaining nuclei, Na, Al, S, and Ca are found to have source abundances of 0.07, 0.11, 0.18 and 0.13 of Fe respectively. The source abundance of C and O relative to Fe is also much different than some earlier compilations. A comparison of solar and cosmic ray abundances reveals certain selective differences, rather than a systematic overabundance of heavy nuclei in cosmic rays, as has been suggested in the past. These differences are discussed in terms of a common nucleosynthesis origin of the two species of particles.

The evolution of massive stars with mass loss

Abstract: The evolution of massive stars is investigated in the phases of hydrogen and helium burning, taking into account the mass-loss due to light pressure in optically thick media. The evolution in the stage of hydrogen burning near the Main Sequence occurs without mass loss. The large inverse density gradient appears in the outer layers of a 30 M⊙ star after it goes into the domain of red super-giants in the helium-burning stage. This effect appears as a consequence of an excess of luminosity of the star the ciritical one in sufficiently extensive outer layer, where convection is not so effective. In this way, the conditions for outflow of matter are formed. The sequence of selfconsistent models is constructed, with the core in hydrostatic equilibrium and hydrodynamically outflowing envelope. The amount of mass loss is not a given parameter, but it is found during the calculations as a characteristic number of the problem. The amount of mass loss is very high, of the order of ≈0.5M⊙ yr, the velocity of the flow is ≈20 km s−1. The star loses about 7.2M⊙ during 15 yr. The amount of mass loss must rapidly decrease or finish altogether when matter near the hydrogen-burning layer begins to flow out, and a transformation of stellar structure must occur.

Orientation of interstellar and interplanetary grains

Abstract: The explicit expressions for the orientation distribution function of interstellar and interplanetary dust grains in the anisotropic corpuscular or radiation fluxes, with consideration for the magnetic field influence, are obtained. An orientation is shown to be possible in a medium having an anisotropic temperature, which is usually the case for a non-equilibrium plasma in a magnetic field. It is noted that the small inhomogeneous dust grains should possess a specific rotation of polarization. The orientation of these dust grains is considered. The time required for the orientation is estimated. A possibility of explaining the interstellar polarization and polarization of the cometary radiation is discussed.

Neutral hydrogen in cometary comas.

Abstract: The strong L alpha radiation observed recently in comets Tago-Sato-Kosaka and Bennett can be explained in terms of the resonant scattering of solar L alpha radiation on neutral hydrogen formed by the photodissociation of H2O which is vaporized from a nucleus having an ice core. A complete hydrodynamic description of an atmosphere composed of H2O and its daughter products OH, H and O coupled through frictional interaction as well as production and loss processes is given. Numerical results are computed in a typical case, and it is found that a temperature of about 3000 K for the cometary atmosphere provides the best fit with observation.

Contributions to the Kinematics of Type I Tails of Comets

Abstract: Observed irregular ‘oscillations’ of the ion tail axis in comets have by some authors been brought in connection with changes in the flow conditions in the solar wind. We are defending in this paper — by arguments resting on well known observations — the conception that these ‘oscillations’ are caused by slight variations in the emission conditions for the ions at their source which has always its place close to the cometary nucleus. A complete renovation of the innermost tail part up to a length of a few million km (called by Hoffmeister the primary tail) and defining the tail axis can take place within a few to several hours. Shifts of this axis are becoming visible when the new tail rays finish their closure along another direction than the earlier ones.

Dust grain origin of cosmic ray air showers

Abstract: It is suggested that cosmic rays of energies as high as 1020 eV consist of dust grains of relativistic energies. Such dust grains as typical in interstellar space are accelerated first by a strong radiation pressure of luminous, compact galaxies and then by magnetic processes. A grain with the mass of about 10−16 g and the Lorentz factor of about 103 attains an energy as large as 1020 eV and produces a huge extensive air shower. Such grains survive against the collisions with cosmic microwave photons. This would remove the serious difficulty, if both the cosmic microwave radiation and the huge extensive air showers, which were regarded as due to protons of energies greater than 1019 eV, existed in spite of that the protons should strongly attenuate by the collisions with the radiation.

Cosmic-ray production of deuterium, He3, lithium, beryllium, and boron in the Galaxy

Abstract: The production of deuterium, He3, lithium, beryllium, and boron by galactic cosmic rays in the interstellar medium, over the life of the Galaxy, is calculated. It is found that high-energy α-α reactions contribute in an essential way to the observed lithium. When allowance is made for the interchange of material between stars and the interstellar gas and for the change of cosmic-ray intensity with time, the Li6, Be9, and boron produced turn out to be ample to explain the observed abundances, and with remarkable internal consistency. Deuterium and He3 arenot produced in significant amounts, nor Li7 in sufficient amount, however. To explain the Li7/Li6 ratio measured terrestrially and in chondritic meteorites, we invoke cosmological production of Li7. This implies the production of deuterium, He3, and He4 as well, in amounts consistent with observation. The theory in its present form cannot explain a solar-system Li7/Li6 ratio of 12and stellar ratios as low as 3, but additional processes can be adduced to reconcile them. The consistency of the numbers when cosmological production is included lends additional support to the big-bang hypothesis. An incidental result is that the mean luminosity of the Galaxy over its lifetime has been about 3 times its present luminosity.

Perturbation of the radial and non-radial oscillations of a star by a magnetic field

Abstract: A generalization of the perturbation method is applied to the problem of the radial and the non-radial oscillations of a gaseous star which is distorted by a magnetic field. An expression is derived for the perturbation of the oscillation frequencies due to the presence of a weak magnetic field when the equilibrium configuration is a spheroid. The particular application to the homogeneous model with a purely poloidal field inside, due to a current distribution proportional to the distance from the axis of symmetry, and a dipole type field outside is considered in detail. The main result is that the magnetic field has a large and almost stabilizing effect on unstableg-modes, particularly on higher order modes. With the considered magnetic field the surface layers appear to have a large weight.

Source models with electron diffusion

Abstract: The general solution for the energy distribution of relativistic electrons in which electrons generated within the source diffuse and decay through synchrotron or Compton radiation is given for the case in which the magnetic field and the diffusion coefficient are constant. A very simple spherically symmetric model with an electron point-source at the centre is considered and the equations are explicitly solved. It is shown that notwithstanding its great simplicity this model gives a fair representation of the continuous emission of the Crab nebula from the radio to the X-ray region, with the simple assumption that it is due only to ordinary synchrotron radiation. If the central point source is identified with the pulsar there appears to be an upper limit of about 107 MeV to the energy of the electrons accelerated by the pulsar mechanism.

Scattering of waves in a magnetoactive plasma

Abstract: A general theory of scattering of waves in a magnetoactive plasma by particles of arbitrary energy is presented. The cross-section for the scattering of magnetoionic waves by thermal particles is derived and discussed. Conditions under which the effect of the spiralling motion of the scattering electron can be neglected in treating inverse Compton radiation are found.

Radial Gradients and Anisotropies Due to Galactic Cosmic Rays

Abstract: Numerical calculations have been made of the radial gradients and the anisotropyvector atr=1 AU due to galactic cosmic-ray protons and helium nuclei. The model used assumes transport by convection and anisotropic diffusion, and includes the energy losses due to adiabatic deceleration. The present calculations are for the 1964–65 solar minimum. An important constraint applied ineach case was that the model reproduces the electron modulation known from deductions of the galactic spectrum and observations of the near-Earth spectrum; and also reproduces the near-Earth proton and helium nuclei spectra. The diffusion coefficients have been based upon those deduced from magnetic-field power spectra.

How are intergalactic filaments made

Abstract: Computer simulations are performed which suggest that narrow intergalactic filaments can be produced by tidal forces. A fixed potential perturber passes a self-gravitating disk of stars in a nearly parabolic orbit. Due to their large velocity dispersion, the stars which are pulled out by the tide form only an amorphous cloud. The gas clouds are simulated by a disk of points of zero mass, zero velocity dispersion superimposed on the stellar disk. The ‘gas clouds’ form remarkably long, narrow filaments; but not so narrow as the narrowest filaments observed.

Some tests of the Vaníček Method of spectral analysis

Abstract: One of the chief claims of the Vanicek Method of spectrum analysis is its, ability to remove ‘systematic noise’ from a time series with minimal distortion of the spectrum of the remaining series. In this paper, comparisons are made between the Vanicek Method and the more usual method consisting of preliminary removal of the systematic noise followed by fourier analysis. Formulas relating the two methods are developed and a series of comparative plots of simple spectra are presented. Results indicate that the Vanicek Method does not displace a spectral peak falling close to the systematic noise, that it distorts the amplitude of the peak less than the conventional method of analysis, and that it tends to intensify the side lobes.

Quantum theory of the dielectric constant of a magnetized plasma and astrophysical applications. I. Theory

Abstract: A quantum mechanical treatment of an electron plasma in a constant and homogeneous magnetic field is considered, with the aim of (1) defining the range of validity of the magnetoionic theory (2) studying the deviations from this theory, in applications involving high densities, and intense magnetic field. While treating the magnetic field exactly, a perturbation approach in the photon field is used to derive general expressions for the dielectric tensor. Numerical estimates on the range of applicability of the magnetoionic theory are given for the case of the 'one-dimensional' electron gas, where only the lowest Landau level is occupied.

The Os-Pt-Hg Abundance Peak in Ap Stars and the Problem of Very Heavy Cosmic Rays

Abstract: Relative abundances in the region 74≤Z≤83 (W to Bi) are determined for 73 Dra, HR 4072, and some other Ap stars. Abundance peaks occur at atomic massesA=191±2 on 73 Dra, atA=201±3 on HR 4072, atA=199±5 on other ‘main’ group Ap stars, and atA=201±2 on Mn stars. Pb has a relatively low abundance on Ap stars and also in cosmic rays which have an abundance peak atA=193±3. The abundance peaks on ‘main’ group Ap stars are due to the cyclicr-process which occurred in explosions of former companion stars. Fission products of transuranic elements are recycled by further rapid neutron captures. At the end of ther-process, the high neutron flux decreases gradually so that the final β-decays take place in a neutron-rich environment; superheavy elements (Z≥110) formed in ther-process may be partly destroyed by neutron-induced fission. The pulsar remnants of the explosions accelerater-process elements to cosmic-ray energies. The peak atA ∼ 201 on Mn stars is discussed briefly.

The equilibrium, stability and evolution of a rotating magnetized gaseous disk

Abstract: The exact solutions for the equilibrium of rotating gaseous disk with poloidal magnetic field are obtained. The stability of the disk with respect to uniform expansion and contraction is investigated by means of the variational principle. It is shown that if the equilibrium is determined by gravitational and magnetic forces only, the disk is in neutral equilibrium with respect to perturbations of the form δr=αr. The instability to short-waves perturbations is studied by the quasi-classical method. The analysis shows that if the magnetic field isH>2πσ√G, where δ is the surface density, then these perturbations are stabilized. The configurations of the electrical field induced by the rotation of magnetized disk are found. In conclusion, the questions of the evolution of the disk are discussed in connection with the quasar model when pulsar-like radiation is taken into account.

Diffuse cosmic gamma rays observed at an equatorial balloon altitude

Abstract: A 3″×3″ NaI(T1) crystal-photomultiplier assembly with a 4π charged particle anticoincidence shield is used to determine the gamma ray spectrum in the energy region of about 100 keV to 8.5 MeV at a balloon altitude of 4.7 g cm−2 over Hyderabad, India (geomagnetic latitude ∼8°N). The atmospheric growth curves are used to obtain the contribution of the diffuse cosmic gamma ray flux in the above energy range. The cosmic photon flux thus deduced up to about 8.5 MeV is consistent with a continuation of the power law spectrum observed at energies between 20 and 200 keV with an index of ∼−2.3, and hence contradicts the flattening trend observed in ERS-18 at an energy of a few MeV.

On the mass-luminosity relation

Abstract: The results of a least-squares study of the mass-luminosity relation for eclipsing and visual binary stars consisting of main sequence components are presented. Two methods are discussed. First, the values of the coefficients A and B in the relation log M = A + BM sub BOL are determined. Then a technique which permits the determination of alpha and beta in the relation M = alpha L beta, when only the sum of the masses, and not the individual masses of each component, is known. The results and a comparison of the two methods are discussed. It is found that the following mass-luminosity relation represents the observational data satisfactorily: log M = 0.504 - 0.103 M sub BOL, -8 less than or equal to M sub BOL less than or equal to +10.5. A discussion of the data and of the possibility that separate mass-luminosity relations may exist for visual and eclipsing binaries is given. The possibility that more than one mass-luminosity relation is required in the range -8 less than or equal to M sub BOL less than or equal to +13 is also discussed.

Astronomical Evidence Concerning Non-Gravitational Forces in the Earth-Moon System

Abstract: The most conspicuous effects of non-gravitational forces in the Earth-Moon system are the accelerations of the Earth's spin and of the Moon's mean angular velocity. Evidence indicates that the present acceleration of the Moon is between −20 and −52 s of arc per century per century and that the present average acceleration of the Earth is between −5 and −23 parts in 109 per century. Over the past 2000 yr, the average for the Moon has been about −42 s per century per century and for the Earth has been about −28 parts in 109 per century; these values are probably correct within 10%. Evidence that does not involve any assumptions about the present values shows strongly that there was a ‘square wave’ in the accelerations that lasted from about 700–1300, and that the accelerations were different by a factor of perhaps 5 during the time of this wave from what they were at neighboring times.