Cosmic ray origin above 1018 eV: Galactic or extragalactic?

An analysis is made of the implications of assuming that suprathermal dust grains (a3×10⁸ cm) of intergalactic origin may acquire cosmic ray energies as high as 10²⁰ eV. These dust grains may attain suprathermal energy (v _g3×10⁸ cm s^–1) by the Fermi process. Initially the dust grains are accelerated by the radiation pressure against the drag of the ambient gas of the medium, but once these dust grains attain a terminal velocity (U10⁵ cm s^–1), then they may be expelled out of the galactic region into the intergalactic medium and finally acquire high energy     

Narrow-band split frequency decimeter solar burst

A wide-band digital decimetric spectroscope is in the process of development at INPE (Brazil), in conjunction with a 9-m diameter polar mounted antenna. Initially, this spectroscope was operating over a narrow-band 1.6 ± 0.05 MHz in an analogue mode. Here we report a slow drifting 5.0 MHz s^-1, narrow-band 1630-1580 MHz, split frequency solar burst lasting for about 15 s, observed on 15 June, 1991. The separation between the split components is 30 MHz, and the upper split frequency component is more intense than the lower split frequency component. These observed characteristics favour the hypothesis of conversion of plasma waves by combinational scattering on upgoing ion-sound waves in a magnetic loop. Existing strong electron density gradients across the magnetic field in the source region will reduce the free-free absorption of radiation at the fundamental frequency. In order to explain the observed temporal characteristics of the upper and lower split frequency components, the radiation has to propagate at some angle to the electron density gradient in the source region. Estimated physical parameters of the source and exciters are as follows: (i) maximum source size (height) 2 × 10⁷ cm; (ii) velocity and length of ion-sound pulse 3.1 × 10⁶ cm s^-1 and 5 × 10⁷ cm, respectively, and (iii) velocity of the exciter of plasma waves (electron or proton beam) 5 × 10⁸ cm s^-1.On leave from the Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia.     

Determination of the total amount of hydrogen atoms in a quiescent prominence

A brief quantitative review of the determination of the chemical composition of the Sun and stars is given. The method of estimation of the total amount of hydrogen atoms in a prominence is considered.The values of relative abundances of some infrequent elements in the solar atmosphere are refined using metal emission lines in the spectrum of a quiescent prominence. The most probable values of relative abundances for itrium _Y1×10^–9, zirconium _Zr2×10^–9, and scandium _Sc3.8×10^–9 are derived.     

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.     

Spectrum of the galactic magnetic fields

The magnetic fields observed in the galactic disc are generated by the differential rotation and the helical turbulent motions of interstellar gas. On the scalesl=2k ^–1 which lie in the intervall ₀<l<l _e (l ₀100 pc is the energy-range scale of the galactic turbulence), the spectral density of the kinetic energy of turbulence (k ^–5/3) exceeds the magnetic energy spectral density (k ^–1). The equipartition between magnetic and kinetic energies is reached atl=l _e 6 pc in the intercloud medium and is maintained down to the scalel=l _d 0.03 pc. In dense interstellar cloudsl _e is determined by the individual cloud size andl _d 0.1 pc.The internal turbulent velocities in Hi clouds (cloud size is assumed to be 10 pc) lie in the range from 1.8 to 5.6km s^–1, fitting well within the observed range of internal rms velocities. Dissipation of the interstellar MHD turbulence leads to creation of temperature fluctuations with amplitudes of 150 K and 65 K in dense clouds and intercloud medium, respectively. The small-scale fluctuations observed in the interstellar medium may arise from such perturbations due to the thermal instability, for instance. Dissipation of the MHD turbulence energy provides nearly half of the energy supply needed to maintain the thermal balance of the interstellar medium.     

Intergalactic suprathermal grains

The physical conditions under which suprathermal grains may loose energy and the processes involving the grains (a3×10^–6 cm) destruction are investigated. It is found that the dust grain once attaining the velocityU (10⁵ cm s^–1) may attain suprathermal energy (v _g3×10⁸ cm s^–1) and subsequently may also attain relativistic energy are almost indestructible in the accelerating phase.     

Anisotropy: High energy cosmic rays and the thermal background radiation

The motion of a large (100 Mpc radius) volume of local matter with respect to the frame in which the thermal cosmic background radiation (CBR) appears isotropic is shown to produce a contribution to anisotropy in the arrival directions of the highest energy (>10¹⁹ eV) cosmic rays. The magnitude of the effect predicted is 1%, below that currently observed and below the sensitivity of present experiments.     

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.     

Cosmic gamma-ray burst from intergalactic relativistic dust grains

Charged dust grains of radiia3×10^–63×10^–5 cm may acquire relativistic energy (>10¹⁸ eV) in the intergalactic medium. In order to attain relativistic energy, dust grains have to move in and out (scattering) of the magnetic field of the medium. A relativistic grain of radiusa10^–5 cm with Lorentz factor 10³ approaching the Earth will break up either due to electrostatic charge or due to sputtering about 150100 km, and may scatter solar photons via a fluorescence process. Dust grains may also melt into droplets in the solar vicinity and may contribute towards observed gamma-ray bursts.     

Variation of Acoustic Power with Magnetic Field as Seen in Gong+ Data

The acoustic spectra in sunspots are known to be richer in higher frequency power. We have attempted a generalized study of the effect of magnetic fields on the shape of the acoustic spectrum using GONG+ bread-board data (spatial scale of 2 arc sec per pixel) of 11 May 2000 and 12 June 2000. The mean power spectra of the velocity oscillations were obtained by averaging over several spectra for different values of the magnetic field. With increasing magnetic field, the acoustic power increases at higher frequencies and decreases at lower frequencies with a transition at 5 mHz. This behavior is slightly different from earlier results obtained from SOHO/MDI data.     

Dynamical friction and the escape of a compact supermassive object shot from the center of a galaxy

A numerical study has been made of the motion of a compact object consisting of a supermassive black hole with a dense cluster of stars around through a galaxy which has recoiled from the center of the latter as a result of anisotropic emission of gravitational radiation or asymmetrical plasma emission. We find that the effect of dynamical friction on its motion through the galaxy (mass10¹¹ M ) estimated using the impulsive approximation technique, is minimal for an object mass 10⁹ M and for recoil taking place at a velocity larger than that of escape. A velocity 1.1 times the escape velocity is needed for the object to escape from the galaxy, whereas for velocities of recoil less than this critical velocity, damped oscillatory motion ensures. The energy exchange of the object with the galaxy is not large enough to cause appreciable change in the internal energy of the latter.     

On the distribution of material as a function of temperature in the post-flare loop system of 12 August 1970

Observations of the post-flare loop system formed after the east limb proton flare of 12 August 1970 include (a) sets of filtergrams from which photographic subtractions have been constructed and (b) spectra from which a distribution of electron density as a function of temperature for three coronal regions are derived. The filtergrams show no indications of radial velocities in excess of 80 km/s. The spectra indicate an increase in density at the tops of the loops with most of the material at a relatively cool temperature: N 6.0 × 10¹⁰, T = 3 × 10⁵K. The distribution functions obtained for areas just above and just below loops indicate a lower electron density and the presence of material at high temperatures, N 2.0 × 10¹⁰ and T 2.6 × 10⁶K (above the loops) and T _e > > 4.4 × 10⁶K for material below the loops.     

Hydromagnetic break-up of bridges and jets into aligned objects

It is shown that a cylindrical plasma column supporting a longitudinal fieldB _z and an azimuthal fieldB has a fastest-growing mode in whichkR ₀1 (k=wave number,R ₀=radius of the column). If we assume that plasma is ejected from a galaxy to form a jet, filament or bridge of length 5 kpc,R ₀0.5 kpc, density 10^–24 gm cm^–3 with a dragged-out field of strengthB _z 10^–5 Gauss (from a parent field 10^–6 Gauss), such a column must eventually fragment by the action of a hydromagnetic instability, breaking up into a number 10 of regularly-spaced condensations. It is, therefore, predicted that features like the M87 jet should show incipient nucleation with 3–10 knots, and that periodically-spaced objects of the type noted by Arp may have resulted from the action of such an instability.     

The classification of stellar spectra using statistical image moments

A modeling of the response of the 1549 CIV emission line profile in the spectrum of Seyfert galaxy NGC 5548 to a sharp continuum drop which happened in 1989 is carried out on the basis of observational data taken from the literature. A more rapid response of the red wing of CIV profile suggesting the accretion of CIV-emitting clouds in the broad-line region (BLR) is reproduced. It is shown that the accretion velocity near the central object is consistent with a free fall law whereas at large distances from the center it varies approximately asr ^–2. The best agreement between observed CIV profile changes and modeled ones is obtained when the mass of the central objectM 1.2 × 10⁸ M . The first approximation of the BLR geometry is also found: the inflow takes place only outside two wide cones with half-opening angle 65° which are disposed like a sand-glass and filled by outflowing material. The angle between the axis of such biconical structure and our line of sight is found to be small ( 9°). It is shown that the outer radius of an accretion disk around the central object does not exceed ~ I light-day (i.e., < 100 Schwarzschild radii), and the outer radius of CIV-emitting BLR is 14 light-days. The nature of a broad blue excess in the CIV profile which did not respond to the continuum change is discussed.     

On the formation of energy spectra in synchrotron sources

The observed energy spectra in synchrotron sources are power laws,N (E)=KE ^–, with the distribution in peaked around 2.5. These are consistent with initially injected spectra with between 1 and 2, subsequently steepened by synchrotron losses. Contrary to the results of Kardashev (1962), it is shown that statistical acceleration when coupled with synchrotron losses lead naturally to the formation of flat stationary spectra with 1. These stationary spectra have bends near the energy at which synchrotron losses balance the energy gains by acceleration. Above this bend the spectrum tends to =2. The time evolution of an initial spectrum towards the stationary spectrum is investigated. It is suggested that the initially flat spectra with 1 to 1.5 observed in some variable sources result from an incomplete approach to the stationary spectrum, and that in sources with constant acceleration spectra with 2 are to be expected.     

On the production of suprathermal grains

The physical conditions under which suprathermal grains can be produced when they are accelerated by radiation pressure against the drag of ambient gas are investigated. It is found that dust grains may attain a terminal velocityU (=10⁵ cm s^–1) in most regions and move out of the midplane of the source region about a distance |z|100 pc. Once clear of the main gas/dust layer the dust grains (a3×10^–6 cm) may then attain suprathermal energy (V _g 3×10⁸ cm s^–1) by the Fermi process.     

Magnetic Dips in Prominences

Magnetic dips are generally assumed to be basic equilibrium configurations in quiescent solar prominences. Here we discuss two types of the magnetic dips which were considered in the literature: (1) dips resulting from a force-free magnetic equilibrium in the corona, and (2) magnetic dips which are formed in situations where the Lorentz force balances the weight of the prominence plasma. An important parameter which decides between these two cases is the plasma . For 1, the effect of the prominence material on the equilibrium structure is quite negligible and the case (1) holds. If, however, is larger, say between 0.1 and 1 or even higher, magnetic dips of the second kind are formed and they can be characterized by the angle 1 between the vertical and the direction of the field lines at the surface of the prominence structure. A simple and illustratory formula is derived to relate this angle to the plasma at the prominence center, namely ccot21. c=1 thus corresponds to 1=45°. Finally, we discuss the range of values of both c and 1 as deduced from various observations and conclude that the dips of the second kind are important for the prominence equilibria. We also suggest a new method for determination of the field-line inclination.     

Cosmic-ray perpendicular diffusion coefficient computed using Voyager data at 15 AU

Perpendicular diffusion due to either field line wandering or random gradient and curvature effects makes a substantial contribution to the radial transport of particles at distances of about 5 AU and beyond when lines of the interplanetary magnetic field (IMF) become almost azimuthal. Here test particle trajectories are followed in a field model which uses a magnetic field sample taken by Voyager 2 at 14.8 AU. Techniques previously developed (Moussas et al., 1982a) are employed to calculate the perpendicular diffusion coefficient for 100 MeV protons and arising from random gradient and curvature effects. The result K=(2.8±0.9)×10²¹ cm² s^–1 shows a substantial increase above the value determined previously at 5 AU and, assuming a power law radial dependence Kr , implies 0.8–1.1. This result is consistent with observations of the cosmic-ray radial gradient.     

V 505 Mon: One of the most massive binaries

From 59 spectra collected at Asiago from 1969 to 1976, we obtain the spectroscopic orbit of the binary V 505 Mon. The rather long periodP=53.7805 days and semiamplitudeK ₁=83±4 km s^–1 of the primary component imply a fairly large mass of the secondary (m ₂3.2±0.4m ). Apparently also lines of this latter have been recorded, thus indicating highly massive components (m ₁50,R ₁=26,m ₂27,R ₂=14, in solar units) in a detached system (separation 255R ). The already reported variation of 0.15 mag., with period about one day, together with H emission, we detected, point toward a possible massive X-ray progenitor.     

Cold plus hot dark matter and structure formation of the universe

Cold plus hot (neutrino) dark matter models are studied and compared with the tilted cold dark matter models (which have a non-Zel'dovich initial density perturbation spectrum). For the hybrid dark matter models, a simpler treatment for the relativistic neutrinos is presented. The numerical results of this treatment are shown to be in good agreement with those given by other authors. Comparing the theoretical and the observational results of the quadrupole fluctuations of the cosmic background radiation and the large-scale velocity field of galaxies, the hybrid dark matter models require a fraction of neutrino density 0.3, a fraction of cold dark matter _c 0.7 and a number of massive neutrino speciesN = 1 for the case of Hubble's constantH ₀ = 50 km s^–1 Mpc^–1. The distribution of comoving number density of quasars at high redshifts is studied using the Press-Schechter theory. The calculations show that the hybrid dark matter model ( _c 0.7, 0.3) and the tilted CDM model withn = 0.7 0.8 both account for the observed quasar abundance at high redshift.