Showing papers in "Astrophysics and Space Science in 1971"
TL;DR: In this paper, the spectral analysis using least squares (LS) is further developed to remove any undesired influence on the spectrum, which can be used for irregularly spaced as well as equidistantly spaced data.
Abstract: The concept of spectral analysis using least-squares is further developed to remove any undesired influence on the spectrum. The influence of such a ‘systematic noise’ can be eliminated without the necessity of knowing the magnitudes of the noise constituents. The technique can be used for irregularly spaced as well as equidistantly spaced data. The response to random noise is found to be constant in the frequency domain and its expected level is derived. Presence of random noise in the analyzed time series is shown to transform the spectrum merely linearly. Examples of applications of the technique are presented.
298 citations
TL;DR: In this paper, a model of the galaxy is constructed and evolved in which the integrated influence of stellar and supernova nucleosynthesis on the composition of the interstellar gas is traced numerically.
Abstract: A model of the galaxy is constructed and evolved in which the integrated influence of stellar and supernova nucleosynthesis on the composition of the interstellar gas is traced numerically. Our detailed assumptions concerning the character of the matter released from evolving stars and supernovae are guided by the results of recent stellar evolutionary calculations and hydrodynamic studies of supernova events. It is difficult to visualize an epoch of massive star formation in the collapsing gas cloud which formed our galaxy which would enrich the gas rapidly enough to account for the level of heavy element abundances in halo population stars; we have therefore proposed a stage of star formation which is entirely pregalactic in character. We suggest that the Jeans' length-sized initial condensations in the expanding universe discussed by Peebles and Dicke may provide the appropriate setting for this first generation of stars. Guided by these considerations, and by the need for a substantial quantity of 'unseen' mass to bind our local group of galaxies, we have constructed a model of the galaxy in which this violent early phase of massive star formation produces both (1) approximately 25% of the level of heavy elements observed in the solar system and (2) an enormous unseen mass in the form of black holes.
214 citations
TL;DR: In this paper, the neutrino spin precession effects in the magnetic field of the Sun are considered as an explanation of the outcome of Davis' solar neutrinos experiments. But, the value for the Neutrino magnetic moment evaluated under these theoretically anomalous circumstances is still so small that only the largest possible estimate for magnetic field strength in the Sun's interior would cause the required effect.
Abstract: Neutrino spin precession effects in the magnetic field of the Sun are considered as an explanation of the outcome of Davis' solar neutrino experiments. Theoretically, it is possible to account for a neutrino magnetic moment only as the result of the interaction of the electromagnetic field with charged particles into which the neutrino can transform virtually. The currently accepted theory of weak interactions (the two component neutrino andV-A interactions) forbids a resulting magnetic moment interaction with the electromagnetic field for all such virtual processes. Modifications of this theory are considered to find out whether an appreciable precession effect is permitted within the experimentally established limits. It is found that the value for the neutrino magnetic moment evaluated under these theoretically anomalous circumstances is still so small that only the largest possible estimate for the magnetic field strength in the Sun's interior would cause the required effect.
202 citations
TL;DR: In this paper, an account of the theory of the light curves of supernovae is presented, based on certain assumptions concerning the passage through the stellar atmosphere of powerful shock waves.
Abstract: An account of the theory of the light curves of supernovae is presented, based on certain assumptions concerning the passage through the stellar atmosphere of powerful shock waves. The investigation is based on numerical integration of appropriate equations of gas dynamics and radiative heat-conductivity. The calculations substantially involve the ionization and recombination of hydrogen in the envelope of a supernova. Changes are traced in the curves arising from the transition from compact stars with small radius (∼10R
⊙), to stars with very extensive envelopes (∼10000R
⊙). The light curves for compact stars agree well with observations of the peculiar supernovae in NGC 5457, NGC 6946 and NGC 5236. The characteristics of the light curves with the passage of shock waves through the extended atmosphere coincide within an order of magnitude with observations of the supernovae of type II and type I near their maximum brightness. A powerful heat-wave propagates before the shock-front in the extensive atmosphere which gives rise to a detached supernova envelope in the form of a thin spherical layer. We investigated the condition in an ascending wave of cooling and recombination in the supernova envelope. It is shown that part of the hydrogen may recombine to attain full transparency for radiation passing through it. The observations are compared with the results of the theory of radioactive decay of the elements. This explanation of the light curves by the passage of shock waves requires energies of 1050 to 1052 ergs, which are in agreement with mechanisms of thermonuclear explosions.
164 citations
TL;DR: In this article, the use of an analysis of Expected Mean Square Deviation to search for periodicities in an observational data sample is described, and the statistic for testing the null hypothesis of non-periodicity is derived from a partitioning of the total sum of squared deviations from the mean.
Abstract: Use of an analysis of Expected Mean Square Deviation to search for periodicities in an observational data sample is described. The statistic for testing the null hypothesis of non-periodicity is derived from a partitioning of the total sum of squared deviations from the mean.
161 citations
TL;DR: In this article, the quasilinear theory of acceleration of relativistic particles by hydromagnetic turbulence is treated in the adiabatic limit of small gyration radius.
Abstract: The quasilinear theory of acceleration of relativistic particles by hydromagnetic turbulence is treated in the adiabatic limit of small gyration radius. The theory is based on the relativistic Vlasov equation; however, a given pitch-angle scattering rate by microturbulence is postulated and is added to this equation. The resulting acceleration is found to be given by a diffusion coefficient in total momentum, which is proportional to the spectrum of turbulence with a rate coefficient γ. γ is a frequency that represents the efficiency of each wave component of the turbulence in producing acceleration. It is given as an integral over the solution of a differential equation in pitch angle. γ is evaluated in various limiting cases and is shown to lead to familiar forms of acceleration, such as Fermi acceleration and magnetic pumping. Thus, a comprehensive theory of these forms of heating is achieved.
94 citations
TL;DR: In this article, the integrals are used to reduce the number of degrees of freedom of a system by applying corrections to the solution at each integration step, and the corrections are determined by using linearized forms of integrals in a least-squares procedure.
Abstract: The numerical integration of systems of differential equations that possess integrals is often approached by using the integrals to reduce the number of degrees of freedom or by using the integrals as a partial check on the resulting solution, retaining the original number of degrees of freedom. Another use of the integrals is presented here. If the integrals have not been used to reduce the system, the solution of a numerical integration may be constrained to remain on the integral surfaces by a method that applies corrections to the solution at each integration step. The corrections are determined by using linearized forms of the integrals in a least-squares procedure. The results of an application of the method to numerical integrations of a gravitational system of 25-bodies are given. It is shown that by using the method to satisfy exactly the integrals of energy, angular momentum, and center of mass, a solution is obtained that is more accurate while using less time of calculation than if the integrals are not satisfied exactly. The relative accuracy is ascertained by forward and backward integrations of both the corrected and uncorrected solutions and by comparison with more accurate integrations using reduced step-sizes.
82 citations
TL;DR: In this paper, the authors investigated the efficiency of this mechanism in order to obtain an indication of the time scale for the propagation of the convective boundary, and showed that Schwarzschild's criterion is fulfilled within a few percent at the innermost interface of the core boundary.
Abstract: In helium-burning horizontal-branch stars, transformation of helium into carbon increases opacity in the convective core. Such a situation can drive an increase of the core-mass extension via the mixing by overshooting. The efficiency of this mechanism is investigated in order to obtain an indication of the time scale for the propagation of the convective boundary. Schwarzschild's criterion is shown to be fulfilled within a few percent at the innermost interface of the core boundary.
82 citations
TL;DR: Galactic cosmic ray transport equation numerical solution for interplanetary region, considering modulation, diffusion, convection and energy loss effects as discussed by the authors, considering the effects of energy loss and energy modulation.
Abstract: Galactic cosmic ray transport equation numerical solution for interplanetary region, considering modulation, diffusion, convection and energy loss effects
73 citations
TL;DR: In the evolutionary phase of central helium burning, models of horizontal-branch stars reach a stage at which an intermediate region is unstable against convection, due to the progressive increase of the core mass by overshooting during the previous evolutionary stages and to the behaviour of the radiative temperature gradient at the core boundary as mentioned in this paper.
Abstract: In the evolutionary phase of central helium burning, models of horizontal-branch stars reach a stage at which an intermediate region is unstable against convection. This feature is due to the progressive increase of the core mass by overshooting during the previous evolutionary stages and to the behaviour of the radiative temperature gradient at the core boundary. By consideration of the typical time scales of propagation of convection and nuclear burning, a partial mixing (semi-convection) can be induced in a region around the convective core.
69 citations
TL;DR: In this article, the authors investigated the premain sequence evolution and the main sequence evolution of stars of 5, 10, 20, 30, 100, and 200 solar masses, and found that the mean densities in the stars are greater, and the surface temperatures are higher than in normal stars.
Abstract: Investigation of the premain sequence evolution and the main sequence evolution of stars of 5, 10, 20, 30, 100, and 200 solar masses. Normal stars in this entire mass range normally convert hydrogen into helium by the CN-cycle on the main sequence. The present hydrogen-helium stars of 5 and 10 solar masses must reach higher central temperatures in order to convert hydrogen to helium by the proton-proton chains. Consequently, the mean densities in the stars are greater, and the surface temperatures are higher than in normal stars. In the stars of 20 solar masses and larger, the proton-proton chains do not succeed in supplying the necessary luminosity of the stars by the time the contraction has produced a central temperature near 10 to the 8th K. At that point triple-alpha reactions generate small amounts of C12, which then acts as a catalyst in the CN-cycle, the rate of which is then limited by the beta-decays occurring within the cycle. During the evolution of these more massive stars, the central temperature remains in the vicinity of 10 to the 8th K, and the surface temperature on the main sequence approaches 100,000.
TL;DR: In this article, the authors considered a dynamical system with three degrees of freedom and showed that it has two or zero isolating integrals (besides the usual energy integral).
Abstract: Dynamical systems with three degrees of freedom can be reduced to the study of a fourdimensional mapping. We consider here, as a model problem, the mapping given by the following equations:
$$\left\{ \begin{gathered} x_1 = x_0 + a_1 {\text{ sin (}}x_0 {\text{ + }}y_0 {\text{)}} + b{\text{ sin (}}x_0 {\text{ + }}y_0 {\text{ + }}z_{\text{0}} {\text{ + }}t_{\text{0}} {\text{)}} \hfill \\ y_1 = x_0 {\text{ + }}y_0 \hfill \\ z_1 = z_0 + a_2 {\text{ sin (}}z_0 {\text{ + }}t_0 {\text{)}} + b{\text{ sin (}}x_0 {\text{ + }}y_0 {\text{ + }}z_{\text{0}} {\text{ + }}t_{\text{0}} {\text{) (mod 2}}\pi {\text{)}} \hfill \\ t_1 = z_0 {\text{ + }}t_0 \hfill \\ \end{gathered} \right.$$
We have found that as soon asb≠0, i.e. even for a very weak coupling, a dynamical system with three degrees of freedom has in general either two or zero isolating integrals (besides the usual energy integral).
TL;DR: In this article, the exact solution for the cosmological equations of Brans and Dicke's scalar-tensor theory when a power law exists between the gravitational constant and the radius of curvature of the universe is sought.
Abstract: The exact solution is sought for the cosmological equations of Brans and Dicke's scalar-tensor theory when a power law exists between the gravitational constant and the radius of curvature of the universe. For the space of negative curvature no solution is possible. On the contrary for a closed space the gravitational constant and the radius of curvature increase linearly with respect to the age of the universe. The parameter ω of the scalar-tensor theory is necessarily negative and can be determined by the present values of the mass-density of the universe, the Hubble-constant and the gravitational constant. The solution has no analogy in Einstein's theory with vanishing cosmological constant, even when the deviations from Einstein's values of the solar relativistic effects are small.
TL;DR: In this paper, the effect of reabsorption and Faraday rotation on the degree of circular polarization in synchrotron radiation has been investigated, and it is shown that the effect is independent of the presence of an ambient medium.
Abstract: Formulas describing synchrotron radiation are extended to include the effect of the presence of an ambient medium and the effect of reabsorption and Faraday rotation on the degree of circular polarization. Results are: (1) The onset of Razin-Tsytovich suppression has no significant effect on the degree of circular polarization. (2) The onset of self-absorption in a source subject to weak Faraday rotation (negligible Faraday rotation in an absorption length) causes the degree of circular polarization to reverse its sign and to decrease (by between one half and one quarter for typical parameters) in magnitude. (3) As in (2) but for strong Faraday rotation (many rotations of the plane of polarization in an absorption length) the degree of circular polarization also reverses its sign and becomes slightly smaller in magnitude than for weak Faraday rotation.
TL;DR: In this article, a fourth-order polynomial method for the integration of N-body systems is described in detail together with the computational algorithm, and a simple method is developed for regularizing an arbitrary number of simultaneous two-body encounters.
Abstract: A fourth-order polynomial method for the integration of N-body systems is described in detail together with the computational algorithm. Most particles are treated efficiently by an individual time-step scheme but the calculation of close encounters and persistent binary orbits is rather time-consuming and is best performed by special techniques. A discussion is given of the Kustaanheimo-Stiefel regularization procedure which is used to integrate dominant two-body encounters as well as close binaries. Suitable decision-making parameters are introduced and a simple method is developed for regularizing an arbitrary number of simultaneous two-body encounters.
TL;DR: In this paper, the energy spectra observed in a CsI crystal in the 20 keV-2 MeV range, due to the decay of radioactive isotopes produced in the crystal by bombardment with 155 MeV protons, are presented as a function of time after irradiation.
Abstract: The energy spectra observed in a CsI crystal in the 20 keV-2 MeV range, due to the decay of radioactive isotopes produced in the crystal by bombardment with 155 MeV protons, are presented as a function of time after irradiation.
TL;DR: In this paper, a kinetic equation for a jet stream consisting of identical, partially inelastic grains in neighbouring orbits around a central gravitating body is derived and given a preliminary discussion.
Abstract: A kinetic equation for a jet stream consisting of identical, partially inelastic grains in neighbouring orbits around a central gravitating body is derived and given a preliminary discussion. No nonsingular equilibrium state exists for the jet stream configuration. The Boyle-Mariotte ideal gas law does not apply. The effect of hard, partially inelastic collisions is to decrease the kinetic temperature of the stream, thereby leading to a lining-up of the orbits of the individual grains with a subsequent reduction in the importance of collisions on the dynamics of the stream.
TL;DR: In this article, the authors pointed out that instabilities play an important role in many of the phenomena of stellar dynamics, such as the formation of spiral arms and the evolution of stellar clusters at a rate faster than one would expect from normal two-body collisions.
Abstract: Indications are that instabilities play an important role in many of the phenomena of stellar dynamics. Examples of such phenomena are: the formation of spiral arms, and the evolution of stellar clusters at a rate faster than one would expect from normal two-body collisions. The analogy with the situation in plasma physics, where similar phenomena are known to be dominated by instabilities, is very suggestive that one might seek for instabilities in stellar dynamics that correspond to similar ones in plasma physics.
TL;DR: In this article, the method of Laumbach and Probstein is applied to a point explosion in a spheroid with exponential density distribution and it is shown that the shock wave propagates strongly along the direction of symmetry axis and the envelope of the shock front elongates to the same direction.
Abstract: The method of Laumbach and Probstein is applied to a point explosion in a spheroid with exponential density distribution. It is shown that the shock wave propagates strongly along the direction of symmetry axis and the envelope of the shock front elongates to the same direction. The rate of elongation of the shock envelope increases with the eccentricity of the spheroid and finally the blowout of the shock wave along the polar axis occurs when the eccentricity exceeds some critical value. It is suggested that such a blowout of the shock may be connected with some galactic outburst having axial symmetry.
TL;DR: In this paper, a new series of neutron star models has been computed and the effects of nuclear dissolution, nuclear forces, and the presence of hyperons were introduced through use of a generalized form of the Levinger-SimmonsVα andVγ potentials.
Abstract: 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-SimmonsVα andVγ 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.
TL;DR: In this article, a detailed technical description of a Monte Carlo scheme for the dynamical evolution of spherical stellar systems is given, as well as a few illustrative results of the method.
Abstract: We give here a detailed technical description of a Monte Carlo scheme for the dynamical evolution of spherical stellar systems The philosophy of the method, as well as a few illustrative results, are given elsewhere (Henon, 1972, hereafter called I)
TL;DR: Pre-main sequence /T Tauri/ stellar evolution, discussing mass loss rates and star formation by interstellar cloud violent hydrodynamic compression is discussed in this article, where the authors also discuss the mass loss rate of stars.
Abstract: Pre-main sequence /T Tauri/ stellar evolution, discussing mass loss rates and star formation by interstellar cloud violent hydrodynamic compression
TL;DR: In this article, it was argued that micro-instabilities of an exact charge neutral magnetopause could lead to a "trapped" particle flow, the absence of which causes the non-existence of an equilibrium magnetospheric boundary layer in the Parker-Lerche model.
Abstract: The way is discussed by which microinstabilities of an exact charge neutral magnetopause could lead to a ‘trapped’ particle flow, the absence of which causes the non-existence of an equilibrium magnetospheric boundary layer in the Parker-Lerche model. Furthermore, it is argued that instead of the non-equilibrium effect of Parker and Lerche, microinstabilities of an exact charge neutral magnetopause might be the underlying physical process of an Axford and Hines' type viscous interaction.
TL;DR: In this article, a hypothesis is put forward that, in the secondary component of ǫ Aurigae, we witness at present, an evolutionary process that may result in the formation of a planetary system very much more massive than our own in the astronomically near future.
Abstract: Recent observations of the eclipsing system of ɛ Aurigae converge to a conclusion that its secondary (‘invisible’) component constitutes a flat disc, some 40 AU across, which is semitransparent, of constant optical depth, and dims light non-selecting without a trace of polarization. Its constituent particles must, therefore, be large in comparison with the wavelength of observation — probably greater, on the average, than 10 μ; with no upper limit imposed by the observations. The mass of this disc appears to be no less than 20 ⊙; and its mean temperature, approximately 500K. The primary component of ɛ Aurigae is an F2 Ia supergiant, probably less than one million years old; while its less massive (and, consequently, less evolved) companion has not yet reached a stellar stage. The external characteristics of this disc-like companion appear to approximate the properties that have frequently been postulated as pre-requisites for the formation of a ‘planetary system’. A hypothesis is put forward that, in the secondary component of ɛ Aurigae, we witness at present, an evolutionary process that may result in the formation of a planetary system very much more massive than our own in the astronomically near future.
TL;DR: In this paper, the character of the nuclear abundances synthesized under explosive carbon, oxygen and silicon burning conditions is demonstrated to be dependent upon the initial metal content of the star Specifically, for metal-poor stars, the calculated abundances both of odd-Z nuclei and of the neutron rich isotopes of even Z nuclei are substantially reduced.
Abstract: The character of the nuclear abundances synthesized under explosive carbon, oxygen and silicon burning conditions is demonstrated to be dependent upon the initial metal content of the star Specifically, for metal-poor stars, the calculated abundances both of odd-Z nuclei and of the neutron rich isotopes of even-Z nuclei are found to be substantially reduced This odd-even effect inZ is consistent with spectral studies of metal deficient stars
TL;DR: In this article, the authors proposed a method to improve the quality of the data collected by the data collection system by using the information of the users' behaviors and the data gathered by the system itself.
Abstract: Изложена теория кривых блеска Сверхновых звезд, основанная на предположении о выходе в атмосферу звезды мощной ударной волны. Исследование опирается на численные расчеты с использованием уравнений газовой динамики и лучистой теплопроводности. Существенным является учет ионизации и рекомбихации водорода в оболочке Сверхновой. Прослежено изменение кривых блеска при переходе от компактных звезд с малыми радиусами (∼10R
⊙) к звездам с очень протяженными оболочками (∼ 10 000R
⊙). Кривые блеска в случас компактных звезд хорощо совпадают с наблюдаемыми у аномальных Сверхновых NGC 5457, NGC 6946 и NGC 5236. Характеристики кривых блеска, получающихся при выходе ударной волны в протяженную атмосферу, по порядку величины совпадают с наблюдаемыми у Сверхновых II типа и I типа вблизи максимума блеска. Распространение перед ударным фронтом в протяженной атмосфере мощной тепловой волны приводит к выбросу оболочки Сверхновой в виде тонкого сферического слоя. Исследованы условия возникновения волны охлаждения и рекомбинации в оболочке Сверхновой. Показано, что часть водорода может рекомбинировать в условиях полной прозрачности по отнощению к излучению. Результаты сравниваются с наблюдениями и с теорией распада радиоактивных элементов. Объяснение кривых блеска выходом ударной волны требует энергий 1050÷1052 эрг, что совместимо с термоядерным механизмом взрыва.