THE RELATIONSHIP BETWEEN SOLAR FLARE GAMMA-RAY EMISSION AND NEUTRON PRODUCTION

We have examined six solar neutron events measured by satellite instruments and/or neutron monitors (NM) to understand the relationship between the intensity–time profiles of the -ray lines, the pion-related -rays, and the neutron production. In all six events the solar neutron production was clearly time-extended. We find that neutron emission as detected by NMs most closely follows the emission of pion-related -rays, whereas lower energy neutron production may follow that of nuclear -ray line emissions. Although this distinction is not unexpected, it is safe to say that the 2.223 MeV -ray line from neutron capture on hydrogen is a poor measure of the neutron production at energies >200 MeV. During the three events on 1982, June 3, 1990, May 24 and 1991, June 4 solar neutrons with energies greater than 200 MeV were recorded by NMs. The NM increases on 1982, June 3 and 1990, May 24 can be modeled using the time profile of the pion-related -rays. For the 1991, June 4 event the NM signal was small but lasted for 60 min and the high-energy -ray data available to us are insufficient to conclude unambiguously that the high-energy neutron production followed the pion-related -rays. In the other three events on 1991, June 9, 11, and 15 solar neutrons with energies 10–100 MeV were observed by the COMPTEL -ray instrument on the Compton Gamma Ray Observatory. The duration of the low-energy neutron production on 1991, June 9 corresponded clearly to the high-energy and not to the low-energy -ray emission.     

Analysis of Multicolor Observations of 3C 66A in 1993-1998

The results of multicolor observations of the blazar 3C 66A, obtained in the course of the project OJ-94, are analyzed. It is established that the energy distribution of the variable source in the optical and IR ranges can be represented, on the average, by a power law: F ^-0.92. Since the blazar's emission is strongly polarized, there is no doubt of the synchrotron nature of the variable source responsible for the blazar's activity.     

Non-radial stellar oscillations: a perspective from potential scattering (I)

This article is the first in a series designed to gain insight into the stellar oscillation problem from a somewhat novel point of view: that of potential scattering, well-known in the quantum mechanical literature. In this paper the known theoretical foundations are developed and applied in the context of the astrophysical problem, wherein the star itself (rather than any portion of it) is the potential which scatters waves and traps them. The basis for the identification of a precisely defined scattering problem is the existence of a linear Schrödinger equation associated both globally (Section 2) and locally (Section 8) with the nonlinear eigenvalue equation for nonradial stellar pulsations. The paper is also designed to be a fairly complete account of the relevant mathematical topics that are germane to a study of this kind. This paper is dedicated to the memory of Professor Zdenèk Kopal, who was a great source of professional encouragement to me during the last fifteen years of his life.     

Velocity dispersion profiles ofN-body simulations

The time evolution of the velocity dispersion as a function of radius, called v-profiles, of threeN-body simulations of Wielen are presented in units ofr/R _G (whereR _G is the gravitational or virial radius) and discussed as a function of mass sample. The evolution of the radial and tangential components of the velocity dispersion is discussed, and each v-profile is fitted to a simple power law in the halo (0.15r/R _G2.0). Several structural features appear at late time intervals: (a) an upturn in the radial component of v which occurs in a decreasing shell (closer to the core) in time, (b) the v-profile of the massive particles mimics that of the total sample, since equipartition of kinetic energy does not obtain, and (c) a local minimum atr0.3–0.5R _G appears in one model which coincides with the local minimum in the number density profiles and possibly with feature (a).The line-of-sight v-profile, called LS-profile, of each model as a function of time and mass sample are also presented and discussed. They contain the same structural features as the v-profiles. Projection factors at small radii are also discussed. The LS-profiles of the models can be compared with the observed velocity dispersion profiles of clusters of galaxies in Struble (1979a).     

Shear angle of magnetic fields

In this paper we introduce a new parameter, the shear angle of vector magnetic fields, , to describe the non-potentiality of magnetic fields in active regions, which is defined as the angle between the observed vector magnetic field and its corresponding current-free field. In the case of highly inclined field configurations, this angle is approximately equal to the angular shear, , defined by Hagyardet al. (1984). The angular shear, , can be considered as the projection of the shear angle, , on the photosphere. For the active region studied, the shear angle, , seems to have a better and neater correspondence with flare activity than does . The shear angle, , gives a clearer explanation of the non-potentiality of magnetic fields. It is a better measure of the deviation of the observed magnetic field from a potential field, and is directly related to the magnetic free energy stored in non-potential fields.     

A momentum distribution of high energy particles around Crab pulsar

We determine the momentum distribution of the relativistic particles near the Crab pulsar from the observed X- and -ray spectra (10³10⁹ eV), provided that the curvature radiation is responsible for it. The power law spectrum for the relativistic electrons,f() ^–5, reproduces a close fit to the observed high-energy photon spectrum. The theoretically determined upper limit to the momentum (due to radiation damping), _M 8×10⁶, corresponds to the upper cut-off energy of the -ray spectrum, 10⁹ eV. The lower limit to the momentum, _m 1.8×10⁵, is chosen such that flattening of the X-ray spectrum below 10 keV is simulated. The number density of these electrons is found to be much higher than the Goldreich-Julian density. We also discuss pulse shape and polarization of high-energy photons. The extremely high density of particles and the steep momentum spectrum are difficult to understand. This may imply that another, more efficient, mechanism is in operation.     

Mgix emission lines in an active region spectrum obtained with the Solar EUV Rocket Telescope and Spectrograph (SERTS)

Theoretical electron-temperature-sensitive Mgix emission line ratios are presented forR _I =I(443.96 )/I(368.06 ),R ₂ =I(439.17 )/I(368.06 ),R ₃ =I(443.37 )/I(368.06 ),R ₄ =I(441.22 )/I(368.06 ), andR ₅ =I(448.28 )/I(368.06 ). A comparison of these with observational data for a solar active region, obtained during a rocket flight by the Solar EUV Rocket Telescope and Spectrograph (SERTS), reveals excellent agreement between theory and observation forR ₁ throughR ₄, with discrepancies that average only 9%. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and also resolves discrepancies found previously when the theoretical results were compared with solar data from the S082A instrument on boardSkylab. However in the case ofR ₅, the theoretical and observed ratios differ by almost a factor of 2. This may be due to the measured intensity of the 448.28 line being seriously affected by instrumental effects, as it lies very close to the long wavelength edge of the SERTS spectral coverage (235.46–448.76 ).     

Expanding and superdense astrophysical systems in general relativistic hierarchical cosmology

A semi-continuous hierarchy, (i.e., one in which there are galaxies outside clusters, clusters outside superclusters etc.), is examined using an expression of the field equations of general relativity in a form due to Podurets, Misner and Sharp. It is shown (a) that for a sufficiently populous hierarchy, the thinning factor( _i+1/ _i [r _i /r _i+1] is approximately equal to the exponentN in a continuous density law (=aR ^–N) provided (r _i /r _i+1)^3-1; (b) that a hierarchical Universe will not look decidedly asymmetric to an observer like a human being because such salient observers live close to the densest elements of the hierarchy (viz stars), the probability of the Universe looking spherically symmetric (dipole anisotropy0.1 to such an observer being of order unity; (c) the existence of a semi-continuous or continuous hierarchy (Peebles) requires that 2 if galaxies, not presently bound to clusters were once members of such systems; (d) there are now in existence no less than ten arguments for believing 2, though recent number counts by Sandageet al. seem to be in contradiction to such a value; (e) Hubble's law, withH independent of distance, can be proved approximately in a relativistic hierarchy provided (i)N=2, (ii)2GM(R)/c ² R1; (iii)Rc (iv)M0 in a system of massM, sizeR (f) Hubble's law holds also in a hierarchy with density jumps; (g)H100 km s^–1 Mpc^–1; (h) objects forming the stellar level of the hierarchy (in a cosmology of the Wilson type) must once have had 2GM/c ² R1; (i) there is a finite pressurep=2Ga in all astrophysical systems (a=R ^N ,N2); (j) for the Galaxy, theory predictsp _G7×10^–12 dyn cm^–2, observation givesp _G5×10^–12 dyn cm^–2; (k) if the mass-defect (or excess binding energy) hypothesis is taken as a postulate, all non-collapsed astrophysical systems must be non-static, and any non-static, p0 systems must in any case be losing mass; (1) the predicted mass-loss rate from the Sun is 10¹² g s^–1, compared to 10¹¹ g s^–1 in the observed solar wind; (m) the mass-loss rates known by observation imply timescales of 5×10⁹ years for the Sun and 10¹⁰ years for other astrophysical systems; (n) degenerate superdense objects composed of fermions must haveN-2 if they were ever at their Schwarzschild radii and comprised a finite numberN _B of baryons; (o)N _B10⁵⁷N for degenerate fermion and boson systems; (p)285-4; (q) the metric coefficients for superdense bodies give equations of motion that imply equal maximum luminosities for all evolving superdense bodies (L _max10⁵⁹ erg s^–1); (r) larger bodies have longer time-scales of energy radiation atL _max (10^–5 s for stars,1 h for QSO's) (s) expansion velocities are c soon after the initial loss of equilibrium in a superdense object; (t) if the density parametera(t) in aR ^–N isa=a (non-atomic constants of physicsc, G, A), andA, thenN=2; (u) N2 is necessary to giveMM at the stellar level of the hierarchy;(v) systems larger than, and including, galaxies must have formed by clumping of smaller systems and not (as advocated by Wertz and others) in a multiple big bang.     

A Survey for Hα emitting galaxies AT z ≃ 2.2

The deepest survey for H emitting galaxies at z 2.2has recently been made in narrow-band ( 1%) filters around2.1m using SOFI at the ESO NTT telescope. An effective area of 100 sq. arcmin and a comoving volume of 9000 Mpc³ (forH₀ = 50, q₀ = 0.5) has been covered to a volume weighted 3 line flux limit of 5 × 10^-17 erg s^-1cm^-2. Our survey covered the WFPC2 and STIS fields in the HubbleDeep Field South and an anonymous field about 30 deg. away. Thefaintest limit reached was 3 × 10^-17 erg s^-1 cm^-2 onthe WFPC2 field. In total, 10 convincing candidates with deduced starformation rates in the range 9 - 50 M/yr and an equal number ofmarginal ones have been identified for confirmation and follow-upspectroscopy with ISAAC at the VLT. Based on a very preliminaryanalysis we compare our results with those of earlier surveys andbriefly discuss some possible implications for the form of theevolution out to z 2 and the effects of clustering.     

Vertical structure of plages

A new spectroscopic method of deriving the three-dimensional information (escalation) worked out at the Pulkovo Observatory was applied to observations of solar faculae. The size of the investigated area was 70 × 18. Two series of spectra were obtained simultaneously in four spectral regions (H, D_1,2, (Nai), H, and H, K (Caii)) with a quadruple-camera spectrograph attached to the second horizontal solar telescope at Pulkovo on 13 August, 1968.It was found from the analysis of the maps of brightness distribution in the cores of the lines and continuum that the facular emission lies in ropes which incline to the solar surface.     

The galactic warp and rotations of the fundamental system

The proper motion in galactic latitude of O-B stars enables us to detect the kinematic behaviour of an optical counterpart of the large-scale warp of the HI gas layer in our Galaxy. A selected set of the proper motions of about 350 O-B stars within 3kpc from the sun (R₀=8.5kpc) is analyzed on the proper motion systems of N30, FK4, and FK5. A remarkable differece in the kinematic behaviour of the warp appears between the old systems (N30 and FK4) and FK5-system. On the old systems, the O-B stars in the belt 8.5kpcR<9.5kpc exhibit a systematic z-motion upward from the galactic plane forl180° and downward forl>180° with the mean proper motions of about ±0".4/century, respectively. On the other hand, the results on the FK5-system show no meaningful systematic z-motion, even though the O-B star layer exterior to the solar circle is inclined (3°) with respect to the galactic plane. These findings can neither be inferred from the model of the oblique material flow nor from the concepts of the precessional stellar rings and of the bending oscillation of a stellar disk. The remarkable difference in the kinematic behaviour of the warp, appearing between the old and new systems, is caused mainly by the conversion of the proper motions on the old systems into those on the J2000.0 frame. The conversion near the galactic plane is given by µ_b(FK4(J2000.0))–µ_b(FK4)–0.50 sinl/century. The implication of this relation is discussed in connection with the warping motion of stars detected here.     

Solar particle propagation from 1 to 5 AU

A statistical analysis of solar particle events, observed by the GSFC-UNH charged particle detector on board Pioneer 10 and Pioneer 11 from March 1972 to December 1974 (from 1 to 5 AU for each spacecraft), is carried out with the goal of experimentally determining the statistical average interplanetary propagation conditions from 3 to 30 MeV. A numerical propagation model is developed that includes diffusion with a diffusion coefficient of the form k _r =k _o r , convection, adiabatic deceleration, and a variable coronal injection profile. The statistical analysis is carried out by individually analyzing each of five parameters (t _max, (t_max), t ₅, ) that are uniquely defined in a solar particle event. Each of the five parameter data sets were analyzed in terms of both a spacecraft-solar flare connection longitude 50°, and a numerical model that employed a variable exponential decaying coronal injection profile.The five individual parameter analyses are combined with the results that the statistical average radial interplanetary diffusion coefficient from 1 to 5 AU is given by k _r = (1.2 ± 0.4) × 10²¹ cm² s^-1 with = 0.0± 0.3 for 3.4 to 5.2 MeV protons and k _r = (2.6 ± 0.6) × 10²¹ cm² s^-1 with () = 0.0± 0.3 for 24 to 30 MeV protons. Using the classical relationship for the radial scattering mean free path _r, i.e. k _r = _r/3, we obtain _r = 0.09 ± 0.03 AU and 0.075 ± 0.020 AU for the low and high energy data, respectively. These results show, from 1 to 5 AU and from 3 to 30 MeV, that _r is both independent of radial distance and approximately independent of rigidity (for _r~P , where P = rigidity, = -0.15 ± 0.20).The above diffusion coefficients are inconsistent With both the predictions of the diffusion coefficient from present theoretical transport models and with the diffusion coefficient used in modulation studies at low energies.     

Ne vii emission lines in the solar EUV spectrum

Recent calculations of electron and proton impact excitation rates in Nevii are used to calculate theoretical emission line ratios involving both n=0 (2–2) and n=1 (2–3) transitions in the 97–895 Å wavelength range. A comparison of these with existing solar observations, obtained by instruments on rocket flights and on the Skylab mission, reveals generally good agreement between theory and observation. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and implies that the latter may be applied with confidence to the analysis of solar and stellar spectra from current and future satellite missions.     

A coronal loop model for the production of X-ray and radio flares in the RS CVn binary HR 1099

The RS CVn binary stellar system HR 1099 is a source of both X-ray and radio flares. We present here a model of the system in which the two types of flare are produced by the same population of mildly-relativistic ( 10) electrons, injected into a coronal loop. After reviewing possible radiation mechanisms we conclude that, given the probable conditions in the flaring region, the radio emission is gyrosynchrotron radiation and the X-ray emission is thermal bremsstrahlung. The thermal X-ray source must lie in the stellar chromosphere, but the apparent absence of plasma absorption at radio frequencies indicates that the radio source is located high in the coronal loop. Using the relationships given by Dulk and Marsh (1982) for the radio emission from a power-law electron energy spectrum,N() ( - 1)^–, we conclude that 3 7, with 30% of the electron population trapped in the radio source. Some implications of these results for one particular version of the model are discussed.     

Effects of metal abundances on the evolutionary period changes of classical Cepheids

Some peculiarities in the behaviour of a model self-gravitating system described by hydrodynamical equations and isothermal equation of state connected with the presence of thermodynamical fluctuations in real systems were investigated in numerical experiment. The values of density and velocity , , respectively, were computed by numerical code perturbed on each time-step and in each computational cell by random values , for modeling such fluctuations. Perturbed values _i = _i + _i ,v _i = _i + v _i were used to initiate the next step of computations. This procedure is equivalent to an introduction into original hydrodynamical equations of Langevin sources which are random functions. It is shown that these small fluctuations (= v =0,² =v ² = 10^–8) grow many times in marginally-stable state.     

Stellar structure with a Boltzmann factor: An extension to chemically heterogeneous H−He-stars

We present an attempt for an extension of the modified Boltzmann model, which was introduced by Callebautet al. (1982) as an improvement of the polytropic models, to the case of chemically-heterogeneous stars in equilibrium, containing H and He, by proposing a density profile of the formp=C ₁ T ^N exp (–_H m(–_*)/kT) +C ₂ T ^N exp (–_He m(–_*)/kT. Analytical properties are derived and numerical as well as analytical arguments are presented for the conclusion that this hypothesis for a density profile imposes an almost constant chemical profile to the model as a whole, thereby making it in this form unsuited for the study of heterogeneous stars. A comparison is made with the former Boltzmann model in the homogeneous limit.     

Massive X-ray binaries: Their physics and evolution

We review various aspects of the evolutionary history of massive X-ray binaries. It is expected that moderately massive close binaries evolve to Be X-ray binaries, while very massive systems evolve to standard X-ray binaries.The compact objects are formed through supernova explosions. The fairly low galactic latitudes of those systems indicate that the explosion should, in general, not have accelerated the system to a velocity larger than 50kms^–1. This implies that the mass of the exploding stars is in general less than 5 to 6M .After the explosion, tidal forces will circularize the orbit of short period systems. Even if the tidal evolution has been completed, the expansion of the optical star during the course of its evolution will continously disturb the stability of the orbit. Short period systems with large mass ratio may eventually become tidally unstable. Cen X-3 may be an example of such a system. The predicted rate of the orbital period decrease of Cen X-3 is in agreement with the observed rate.A way to represent the rotational and magnetic evolution of neutron stars in close binary systems is presented. The observed distribution of the pulsation periods of X-ray pulsars with Be companions is consistent with initial magnetic fields of 10¹²–10¹³ G of the neutron stars. We suggest that the fast X-ray pulsars 4U 0115+63 and A 0538-66 are young neutron stars, while Cen X-3 and SMC X-1 are recycled pulsars.The evolutionary relationship between massive X-ray binaries, binary pulsars, and millisecond pulsars is also discussed.Invited paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Abundances of heavy elements in the sun

Solar abundances have been derived for Pb, Bi, Th and U. For the three first elements, the abundances are determined from the profiles of their lines obtained with the high resolution solar spectrometer installed at the Jungfraujoch Scientific Station (Switzerland) and from new oscillator strengths based on life-time measurements (Pb and Bi). The possible presence of U in the solar spectrum is also examined.Our results are (in the log N _H = 12.00 scale): logN _Pb = 1.83, logN _Bi 0.80, logN _Th = 0.82, and logN _U 0.60.The meaning of these new solar abundances is discussed from the point of view of the nucleosynthesis theories.This work has been sponsored in part by the Air Force Cambridge Research Laboratories, OAR, through the European Office of Aerospace Research, U.S.A.F., under Contract AF 61 (052)-955 and by the Comité National Belge de la Coopération Géophysique Internationale (C.N.B.C.G.I.).     

On the coupling of lunisolar resonances for Earth satellite orbits

The resonance C1 occurs when the longitude of the perigee measured from the equinox becomes a slow angle in the doubly averaged equations of motion. This resonance is one of the critical inclination family with I 46°. For prograde Earth satellite orbits, up to five critical points can be identified. Only simple pitchfork bifurcations occur for the single resonance C1. A two degrees of freedom system is studied to check how a coupling of two lunisolar resonances affects the results furnished by the analysis of an isolated resonance case. In the system with two critical angles (g+h and h,+2 , seven types of critical points have been identified. The critical points arise and change their stability through 11 bifurcations. If the initial conditions are selected close to the critical points, the system becomes chaotic as shown in Poincaré maps.     

Stability of outer planetary orbits around binary stars: A comparison of Hill's and Laplace's stability criteria

A comparison is made between the stability criteria of Hill and that of Laplace to determine the stability of outer planetary orbits encircling binary stars. The restricted, analytically determined results of Hill's method by Szebehely and co-workers and the general, numerically integrated results of Laplace's method by Graziani and Black are compared for varying values of the mass parameter =m ₂/(m ₁+m ₂). For 00.15, the closest orbit (lower limit of radius) an outer planet in a binary system can have and still remain stable is determined by Hill's stability criterion. For >0.15, the critical radius is determined by Laplace's stability criterion. It appears that the Graziani-Black stability criterion describes the critical orbit within a few percent for all values of .