The effect of chemical abundance oscillations on the pulsational properties of A 5M ⊙ hydrogen-helium star

A model of a first generation intermediate star of 5M , with Z=0 has been considered. The model is at an advanced stage of its evolution and has a double shell burning. It burns helium in the inner shell, and hydrogen, via CNO cycle, in the outer shell. =(log/log) _T and _T =(log/logT) were computed allowing for the oscillations of the relative mass abundance of the reagents in nuclear reactions. Including =(log/log) _T and =(log/logT) of mean molecular weight and the effect of the oscillations of abundances due to nuclear reactions, stability was studied. Contrary to the results of the static calculations, we found that instability due to the excitation mechanism provided by the high temperature sensitivity of energy generation rate propagates up to the surface. Thus the model in question was found to be unstable against radial adiabatic pulsations, in its fundamental mode.     

О влиянии флукаций электронной концентрации на меру дисперсии и мету вращения

, (DM) (RM). , DM RM N _e = n _e ds. M _e = n _e H cos ds ; . Lerche (1970a, b) , DM RM N _e M _e . .     

Regulation of solar wind heat flux by ordinary mode instability

The ordinary mode can frequently become unstable in the solar wind at 1 AU provided the ratio of halo to core electrons density does not exceed the value 0.05. The growth rates corresponding to the average conditions are typically 10 _P ( _P being the proton cyclotron frequency). Because of low threshold for onset of instability for _C 1 (where _C is the transverse beta for the core electrons), the mode is expected to play an important role in regulating the solar wind heat flux at 1 AU.     

On the relation between solar-flare gamma-ray emission and proton escape into interplanetary space

It is shown that escaping of solar flare energetic protons into interplanetary space as well as their relation to the flare gamma-ray emission depend on the parameter = 8p/B ₀ ² , where p is the pressure of hot plasma and energetic particles and B ₀ is the magnetic field in a flaring loop. If 1, the bulk of the energetic protons escape to the loss cone because of diffusion due to small-scale Alfvén-wave turbulence, and precipitate into the footpoints of the flaring loop. The flare then produces intense gamma-ray line emission and a weak flux of high energy protons in interplanetary space. If >_*0.3-1.0, then fast eruption of hot plasma and energetic particles out of the flaring loop occurs, this being due to the flute instability or magnetic-field-plasma nonequilibrium. The flare then produces a comparatively weak gamma-radiation and rather intense proton fluxes in interplanetary space. We predict a modulation of the solar flare gamma-ray line emission with a period 1 s during the impulsive phase that is due to the MHD-oscillations of the energy release volume. The time lag of the gamma-ray peaks with respect to the hard X-ray peaks during a simultaneous acceleration of electrons and protons can be understood in terms of strong diffusion.     

Gravitational orbit-attitude coupling for very large spacecraft

Motion equations for the gravitationally coupled orbit-attitude motion of a spacecraft are presented. The gravitational force and torque are expanded in a Taylor series in the small ratio (spacecraft size/orbital radius). A recursive definition for higher moments of inertia is introduced which permits terms up tofourth order to be retained. The expressions are fully nonlinear in the attitude variables. A quasi-sunpointing (QSP) passive attitude-control mode is used to assess the effects of higher moments of inertia and gravitational coupling. The attitude motion is detectably coupled to the orbital motion. However, the higher moments of inertia influence only the attitude motion.Nomenclature f _G ,g _G ,f _Gi ,g _Gi total gravitational force and torque and their components of orderi in =/r ₀ - angular momentum of spacecraft about 0 and the spacecraft mass center - J ⁱ ,I ⁱ general moment of inertia about 0 and the spacecraft mass center - second (dyadic), third (triadic), and fourth (tetradic) moment of inertia about 0 and the spacecraft mass center - A andB (and related components) of the second, third and fourth moments of inertia about 0, see Equation (9) - M, m Earth's mass, spacecraft mass - Q ^ba rotation matrix taking _a into _b - position vector from attracting body's mass center to a general mass element, to 0 and to the spacecraft mass center - ₁, ₂, ₃ basis vectors of reference frame - , , _N misalignment angle betweenb ₃ and the (projected) true position of the Sun, its oscillatory component and nominal value - unit dyadic (-identity matrix) - ratio of characteristic spacecraft dimension to orbital radius - pitch angle (aboutb ₂ axis) - Earth's gravitational parameter - , position vector from 0 to a general mass element and the spacecraft mass center - , the (projected) true longitude of the Sun and the true longitude of the spacecraft - _/ angular velocity of reference frame with respect to - (·), (^*), (^o) d()/dt with respect to inertial space _I , and orbiting frame _O and a body-fixed spacecraft frame _b Presented at AAS/AIAA Astrodynamics Conference, Aug. 9–11, 1982.     

The interaction of matter and radiation in the hot model of the Universe,II

Heating of the primaeval plasma prior to the epoch of recombination results in distortions in the Rayleigh-Jeans region of the microwave relic radiation spectrum (1–60 cm, or more exactly =2.5_–7/8 cm). The present observational data allow limits to be set to such energy injection from which follow upper limits to (a) the amount of antimatter in the universe; (b) the parameters of primaeval turbulence; and (c) the adiabatic fluctuation spectrum for small masses (M<10¹¹ M ).If the heating takes place prior to the epocht=10_1012/5 sec (and in particular at the annihilation of electron-positron pairs atT10⁸–10¹⁰ K,t<300 sec), no observable distortions are expected in the relic radiation spectrum. Here =/_crit is the dimensionless average density of matter in the universe.Translated from the Russian by D. F. Smith.     

Роль диффузного вешества В коронах галктик

I I I : M_gas<0.04 M_cor. - . , .     

Relativistic supermassive stars

A plausible scenario for the formation of a stable supermassive star in the relativistic regime has been discussed. The onset of the negativity of the `distribution function' in the stable sequences of the star clusters [the stability of star clusters is assured by using the variational method (Chandrasekhar, 1964a,b) for equivalent gas spheres] described by Tolman's type VII solution with vanishing surface density has been regarded as an indication of the conversion of the cluster structure into a supermassive star. For the critical values of the `adiabatic index', (4/3) < _crit (5/3) (forwhich a supermassive star represent neutrally stable system), the mass, and the size of this object comes out to be 6.87 × 10⁷ M M 1.7 × 10⁹M, and 2.74× 10¹⁴ cm a 1.43× 10¹⁵cm respectively, for the central temperature,T₀ = 6× 10⁷°K, which is sufficient for the release ofnuclear energy. The total energy released during their evolution rangesfrom 2.46× 10⁶⁰ - 3.18× 10⁶² erg, which is sufficient to power these objects at least for a period of 10⁶ - 10⁷years. These figures agrees quite well with those cited for Quasi Stellar Objects (QSOs) in the literature.     

Observed oddities in the lines H,K, b and Hβ

We compare microphotometer intensity traces perpendicular to dispersion in simultaneous spectrograms of good spatial resolution traced at various 's in each of the lines. Cross correlations between the different traces show the following: (a) For each _K there is a corresponding _{b 1}at which the coefficient of correlation, r, is a maximum, usually > 0.8. (b) No such high correlations are found between H and H. (c) Comparison of traces in the continuum and at all observed 's in K, H, b₁, b₂ show a range of 's in each line over which r is very significantly negative, while H shows no such peculiarity.     

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 ).     

Rapid simultaneous observations of Feii and Balmer emission lines of X Oph

Sudden brightening of FeII and Balmer (H and H) lines of X Oph was observed on 28–29 May, 1986. Equivalent width of FeII and H lines increased by a factor of two and that for H line by a factor of four, during the brigtening phase of the star. This brightening phenomena has been explained in the framework of Coronal Radiative Instability.     

An investigation on H-R diagrams of globular clusters

The most characteristic features of H-R diagrams of blobular clusters are summarized with particular regard to the position and the extension of the horizontal branch. A comparison of observations with theory in the two cases of evolution with and without mass loss is then shortly given.A preliminary approach to the evolution of models with large mass fractions (q ₀) in the helium cores is presented. Inhomogeneous equilibrium models with double energy sources have been computed in a range of values ofq ₀ and of the total mass referring to possible horizontal-branch stars.

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Riassunto Sono indicate le principali caratteristiche dei diagrammi H-R degli ammassi globulari con particolare riferimento alla posizione ed alla estensione del ramo orizzontale. Sono esaminate relazioni tra la teoria ed i parametri indicati nei due casi di evoluzione con e senza perdita di massa.E' presentata infine una analisi di modelli con un'alta frazione di massa nel nucleo di elio (q ₀). I modelli di equilibrio, non omogenei ed a doppia sorgente di energia, sono stati calcolati in un intervallo di valori diq ₀ e della massa totale che sono in relazione alla regione delle stelle del ramo orizzontale.

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- . . . q ₀ . q ₀ .

     

Scanner observations of the Be starsν Gem,κ Ori,β Mon andω CMa

The photoelectric spectrophotometric scans of the Be stars Gem, Ori, Mon and CMa have been analyzed to find out few stellar parameters. The absolute energy distributions of these stars in the wavelength range 350–750 nm have been given. Their effective temperatures and gravities have been estimated from comparisons with non-LTE model atmospheres. The stars Gem and Mon have been found to have Balmer discontinuities in emission. The excess emission in the region 620–750 nm has been observed for Mon and CMa. The evolutionary aspects of these stars are discussed and their masses have been estimated.     

Plasma Beta above a Solar Active Region: Rethinking the Paradigm

In this paper, we present a model of the plasma beta above an active region and discuss its consequences in terms of coronal magnetic field modeling. The -plasma model is representative and derived from a collection of sources. The resulting variation with height in the solar atmosphere is used to emphasize that the assumption that the magnetic pressure dominates over the plasma pressure must be carefully employed when extrapolating the magnetic field. This paper points out (1) that the paradigm that the coronal magnetic field can be constructed from a force-free magnetic field must be used in the correct context, since the force-free region is sandwiched between two regions which have >1, (2) that the chromospheric Mgii–Civ magnetic measurements occur near the -minimum, and (3) that, moving from the photosphere upwards, can return to 1 at relatively low coronal heights, e.g., R1.2 R _s.     

Supersymetric Taub model,the micro-superspace sector

Since there are reasons for expecting supersymmetry in an underlying quantum theory of gravity, one is led to study quantum and classical cosmology with supergravity. In particular, classical solutions corresponding to these models could also be used to generate the quantization of supersymmetric minisuperspaces. In generating these solutions, the solution to the Rarita-Schwinger field in the cosmological background is also obtained. In this paper the supercosmological equations of Einstein-Rarita-Schwinger are solved for the micro-superspace sector of the Taub model, under the assumption =₁₁*₂₂ and . The solution for the parameters of the metric and are proportional to each other in each order, the zeroth-order and also the second-order terms. The zeroth-order terms correspond to the solution in general relativity and are logarithmic in time, the ₁₂ terms have an hyperbolic time-dependence. The Rarita-Schwinger field has the form cos((2/D ³)ln |t–t ₀|) and oscillates an infinite number of times astt ₀. This oscillating behaviour of the solution for is not only present when spinor fields are treated in a curved background, but also some cosmological wave functions behave in this manner. This solution is at the same time the supercosmological solution for the microsuperspace sector of the Taub model and also the Rarita-Schwinger field in this background.This work was supported in part by CONACYT grant P228CCOX891723, and DGICSA SEP grant C90-03-0347.     

Оптимальное демпфирование нутационного движения спутников, стаБилизируемых вращением

, . , , . , , -, This article investigates the dynamics of a system for damping the nutating motion of a spin-stabilized satellite. The equations of motion of the satellite-damper system are derived omitting consideration of the influence of external torques. The conditions of stability of the stationary spinning are obtained and the optimal parameters of the satellite and the damper ensuring a maximal rate of damping of the nutation motion are determined.     

Bidimensional spectroscopy of network bright points

We develop an automatic, computer controlled procedure to select and to analyze the Network Bright Points (NBPs) on solar images. These have been obtained at the Sac Peak Vacuum Tower Telescope by means of the Universal Birefringent Filter and Zeiss H filters, tuned, respectively, along the profiles of the H, Mg-b1, Na-D2, and H lines.A structure is identified as an NBP if at the wavelength H- 1.5 A its maximum intensity is greater than I + 3 and its area is greater than 1.5 arc sec² at I + 1.5, where I is the mean value and the standard deviation of the intensity distribution on the image. Each detected NBP is then searched and confirmed in all the remaining 31 images at different wavelengths.For each NBP several parameters are measured (position, area, mean and maximum contrast, Dopplergram velocity, compactness, and so on) and some identification constraints are applied.The statistical analysis of the various parameter distributions, for NBPs present within an active region and its surroundings, shows that two types of NBPs can be identified according to the value of their mean contrast C _min the H- 1.5 Å image (C _m 0.1 type I, C _m> 0.1 type II). The type I NBPs (all occurring on the boundaries of the supergranular network) appear to be much more frequent (180/26) than the type II ones.The size A of type I NBPs is less than 1.0 arc sec for H/H wings but of the order of 1.2 arc sec for Na-D2 and Mg-bl. The mean contrast C _m is around the value of 10% along the Na-D2 and Mg-bl profiles and of 20% along the H/H wings.The C _m - A scatter diagrams show, for the photospheric radiation (h < 100 km), a narrow range of variability for C _min correspondence with a wide range for A. For radiation orginated at higher levels (h > 200 km), the C _m- A scatter diagrams seem to indicate, even if with a large variance, that the highest C _m's tend to correspond to the highest A values.The mean Doppler shift is close to zero for Na-D2 and Mg-bl lines but negative (downward motion) for H and H lines.The type II NBPs tends to be preferentially located in the neighbourhood of small, compact sunspots and their detectability is almost constant through all the 4 studied line profiles. No conclusions can be derived on the mean size, contrast and Doppler shift values because their distributions are too dispersed. The only positive information is that its C _m- A scatter diagram, in H and H wings, indicates a wide range of variability for C _m in correspondence with very narrow range of variability for A.     

Stellar luminosities and radii fromuvbyβ photometry

A linear relation is found to exist between the Barnes-Evans visual surface brightness parameterF _V and the (b-y)₀ colour index ofuvby photometry for spectral types later than G0. Using this relation, and a previously determined relation for spectral types B0-G0, tables of intrinsic colours and indices, absolute magnitude and stellar radius are given for the ZAMS and luminosity classes Ia-V over a wide range of spectral types. Comparison of absolute magnitudes and radii calculated fromuvby photometry with values obtained using the visual magnitude, parallax and angular diameter indicates thatuvby photometry can be used to determineM _V to ±0 ^m .2 and log(R/R ) to ±0.05.     

Planetary nebulae in planetary and binary systems

The problem of the survival of a low-mass secondary orbiting a primary that becomes a planetary nebula is studied. The values of the mass of the primary are 1.0, 1.5, and 2.0M ; the values of the mass of the secondary 0.001M , 0.01M and 0.1M . The orbital decay and mass of the secondary due to accretion and gravitational drag in the common envelope are presented. The possible application of the results to V471 Tau, UU Sge, WZ Sge and the Sun-Jupiter system are discussed.     

The restricted problem of n+ν bodies

The simplest, conventional, and original form of the circular restricted problem of three bodies is briefly described in sidereal and synodic systems using dimensional and non-dimensional variables. This dynamical system is generalized to n2 primary bodies (from n=2) with masses M_i, 1in, interacting with arbitrary force laws (instead of only gravitational forces). The number of bodies of small mass mM_i not perturbing the primaries is increased from =1 to 1 where 1 and the minor bodies are allowed to interact with one another under arbitrary force laws. While the minor bodies (m) do not affect the motions of the primaries (M_i), the primaries influence the motions of the minor bodies with arbitrary force laws.For the case where n=2, 1, and only gravitational forces act on the system, an integral of the system is derived. It is shown that the energy integral of the general problem of N bodies and the Jacobian integral of the classical restricted problem of three bodies are limiting cases of this integral. The role of the integral in bounding the motion of the minor bodies is discussed. Several applications of this system are given.