Theoretical studies of the flux and energy spectrum of gamma radiation from the Sun

The purpose of this work is to study the various -ray-production mechanisms in solar flares and to calculate the flux, the spectrum, and the decay curves of radiation. Using the continuity equation and taking into account the energy losses for solar-flare-accelerated particles, we obtain the time-dependent particle distribution and thus the time behavior of the resulting rays. The important processes for producing rays in solar flares are found to be nonthermal electron bremsstrahlung, decay of neutral mesons, positron annihilation, neutron capture, and decay of excited nuclei. The results are applied to several known solar flares. For a large flare such as the class 3⁺ on February 23, 1956, continuous rays with energies up to 100 MeV from electron bremsstrahlung and neutral meson decays are observable at the orbit of the Earth by existing -ray detectors. Line rays from positron annihilation (0.51 MeV), neutron capture (2.23 MeV), and deexcitation of excited nuclei O¹⁶ (6.14 and 7.12 MeV) and C¹² (4.43 MeV) are particularly strong and well above the continuous -ray background due to electron bremsstrahlung. These lines can be detected at the Earth.NASA-NRC Resident Research Associate.     

The synthesis of helium and CNO isotopes in massive stars

We present helium and CNO isotopic yields for massive mass-losing stars in the initial mass range 15M M _i 50M . We investigate their dependence on assumptions about mass loss rates, internal mixing processes, and metallicity, and specify the contributions from stellar winds and from supernova ejecta.     

The importance of anisotropic interstellar turbulence and molecular-cloud magnetic mirrors for galactic cosmic-ray propagation

Recent studies suggest that when magnetohydrodynamic (MHD) turbulence is excited by stirring a plasma at large scales, the cascade of energy from large to small scales is anisotropic, in the sense that small-scale fluctuations satisfy the inequality k k , where k and k are, respectively, the components of a fluctuations wave vector and to the background magnetic field. Such anisotropic fluctuations are very inefficient at scattering cosmic rays. Results based on the quasilinear approximation for scattering of cosmic rays by anisotropic MHD turbulence are presented and explained. The important role played by molecular-cloud magnetic mirrors in confining and isotropizing cosmic rays when scattering is weak is also discussed.     

Characteristics and interpretation of the photometric variability of eta carinae and its nebula

A short review is given on the history of the peculiar variable object Car and on a number of relevant references describing and discussing its physical characteristics and behaviour, based on different types of observational techniques. The star is known to be variable since the 17th century. The excessive mass loss to which it was subject during the 19th century is now visible as an ellipsoidal reflection nebula of 15 diameter: the so-called homunculus. The remainder of the paper is spent on different kinds of problems partly based on the results of a decade of photometric monitoring in the VBLUW photometric system of Walraven. Foreground reddening and reddening by dust in the homunculus are determined and amount to E(B - V) _J = 0 50 and < 6, respectively. Scanning of the homunculus revealed an estimate for the photometric characteristics of the central object, which presumably consists of a massive hot star surrounded by a cooler gas envelope. The total luminosity is derived using fluxes of various sources in the wavelength region 0.15 < < 175 n resulting in M _bol = - 12 3 ± 0 2. The total observed flux corrected for foreground extinction corresponds to a star with R 96 R if T _eff 30 000 K. The mass may be near 150 M . The excess luminosity in 1843, when the star was presumably bolometrically at least 2 5 brighter than at present, may have been caused by envelope-energized pulsations when the star's luminosity was close to its Eddington limit. The temperature should then have been 50 000 K. The mass loss rate, during the excess luminosity phase lasting 30 yr, is estimated to amount to M 4 × 10^-3 M yr^-1. At present the mass loss may be M 10^-4M yr^-1. Since the homunculus is mainly built up from material expelled in the 30 yr interval (from 1830 to 1860), its total mass amounts to M _hom 0.15 M . The historical observations of the colours of Car and a comparison with the characteristics of S Dor type stars, suggest that Car was subject to a number of S Dor type phases similar to those of P Cyg (in the 17th century), S Dor and others. A satisfactory explanation is found for the complete historical light curve. The decrease in light after the 1843 maximum by 9 ^m , presumably consists of a fading of the luminosity excess and the S Dor effect by 2 5 and 3^m, respectively, and a 3 5 extinction by circumstellar dust. The small amplitude light variations which Car showed during the last decade, were studied with the aid of the variations of the Balmer jump. They are presumably caused by temperature variations of the central star.Percy and Welch (1983) (Publ. Astron. Soc. Pacific 95, 491) have observed P Cyg on a number of nights in 1982 and found for the photometric variations a time scale of 30 to 50 days and an amplitude of 0 _. ^m 15.Based partly on observations collected at the ESO, La Silla, Chile.     

Fourier parameters of heliospheric current sheet and their significance

If the path of the neutral line on the coronal source surface is expressible as a singlevalued function (colatitude vs longitude ), then Fourier analysis of ctn with respect to leads to a simple algorithm for realistically mapping the neutral line outward to model the heliospheric current sheet (HCS) at distancesr1 AU. To be compatible with MHD, the source surface used for this mapping should be prolate (aligned with dipole axis) rather than spherical. Orientation of the Sun's magnetic-dipole moment is indicated by them=1 Fourier amplitude (a ₁ sin +b ₁ cos ) of ctn on the source surface. Physical features (including the neutral line) on a prolate source surface intrinsically map to lower dipole latitudes atr1 AU in the heliosphere, and Ulysses observations of a unipolar field at latitudes beyond 30°S (when the neutral line on the source surface still reached 39°S) confirm the expected geometry.     

Some results of ionospheric investigations by means of coherent radiowaves emitted by satellites

In this paper we discuss theoretical expressions, determining the difference of Doppler shifts of various coherent radiowave frequencies emitted by a radiator moving in the ionosphere or interplanetary medium. The rotating Doppler effect (Faraday effect) caused by the Doppler shifts ±H of the ordinary and extraordinary waves is also considered. In a three-dimensional inhomogeneous ionosphere, stationary in time (N/t = 0), is determined in the general case, by an equation with three variables. The equation for proper depends only on the local value of the electron concentration N _c around the radiator and on integral values, determining, by means of additional calculations, the angle of refraction or its components, the horizontal gradients of electron concentration N/x and N/y, and in some cases, the integral electron concentration ₀ ^zcN dz. We describe the analysis of the measurements, made with the satellites Cosmos I, II and partially XI, assuming that N/t = N/y = 0, with a two variables equation. The expected errors are considered. The results coincide well for different points (Moscow, The Crimea, Sverdlovsk) and thus agree with the measurements of _H and with height-frequency ionospheric characteristics. The curve giving electron concentration versus height N (z) in the outer ionosphere (above the maximum of F2), shows a new maximum higher than the main maximum of the ionosphere N _MF2 at 120–140 km. At this maximum the value of N (z) is (0.9–0.95) N _MF2. The new data on the large-scale horizontal inhomogeneities of the ionosphere, exceed the previous ones by about a factor 10. By means of the irregular variations of the spectrum W() of the inhomogenous formation is determined. Three unknown constant maxima with values 16 to 18 km, 28 to 32 km and 100 to 120 km are found. The spectrum W () mainly characterizes the local properties of the ionosphere along the orbit of the satellite.     

The population of massive stars in R136 from HST/FOC UV observations

New ultraviolet (1300 A, 3400 A),HST FOC observations have been used to derive the UV color-magnitude diagram (CMD) of R136, with the main scientific goal of studying the upper end of the stellar mass function at ultraviolet wavelengths where the color degeneracy encountered in visual CMDs is less severe. The CMD has been compared to a set of theoretical isochrones, which have been computed using the latest generation of evolutionary models and model atmospheres for early type stars. Wolf-Rayet stars are included. Comparison of theTheoretical andobserved CMD suggests that there are no stars brighter than M₁₃₀–11. We use the observed main sequence turn-off and the known spectroscopic properties of the stellar population to derive constraints on the most probable age of R136. The presence of WNL stars and the lack of red supergiants suggests a most likely age of 3±1 Myr. A theoretical isochrone of 3±1 Myr is consistent with the observed stellar content of R136 if the most massive stars have initial masses around 50 M.Bases on Observations with the NASA/ESA Hubble Space Telescope, obtained at the STScI, which is operated by AURA, Inc., under NASA contract NAS5-26555.Astrophysics Division, Space Science Department, ESA     

Characteristics of nearby interstellar matter

There is a warm tenuous partially ionized cloud (T10⁴ K,n(HI)0.1 cm^–3,n(Hii 0.22–0.44 cm^–3) surrounding the solar system which regulates the environment of the solar system, determines the structure of the heliopause region, and feeds neutral interstellar gas into the inner solar system. The velocity (V–20 km s^–1 froml335°,b0° in the local standard of rest) and enhanced Caii and Feii abundances of this cloud suggest an origin as evaporated gas from cloud surfaces in the Scorpius-Centaurus Association. Although the soft X-ray emission attributed to the Local Bubble is enigmatic, optical and ultraviolet data are consistent with bubble formation caused by star formation epochs in the Scorpius-Centaurus Association as regulated by the nearby spiral arm configuration. The cloud surrounding the solar system (the local fluff) appears to be the leading region of an expanding interstellar structure (the squall line) which contains a magnetic field causing polarization of the light of nearby stars, and also absorption features in nearby upwind stars. The velocity vectors of the solar system and local fluff are perpendicular in the local standard of rest. Combining this information with the low column densities seen towards Sirius in the anti-apex direction, and the assumption that the cloud velocity vector is parallel to the surface normal, suggests that the Sun entered the local fluff within the historical past (less than 10 000 years ago) and is skimming the surface of the cloud. Comparison of magnesium absorption lines towards Sirius and anomalous cosmic-ray data suggest the local fluff is in ionization equilibrium.Reason has moons, but moons not hers, Lie mirror'd on her sea, Confounding her astronomers, But, O! delighting me.Ralph Hodgson     

Three-dimensional energetic ion observations and the tangential magnetopause electric field

Three-dimensional distributions for 24.0–44.5 keV protons (ions) are presented from the ISEE-1 medium energy particles instrument during a magnetopause traversal at 01:10 UT on 20 November 1977. Local time of the traversal was 1030. Ion fluxes were observed coming generally from the subsolar region, but over a wide range of latitudes. Enhanced fluxes were observed at the magnetopause crossing with strong components from the subsolar region and from the +Z _SE direction. These observations are compared with the simultaneous electric field observations presented by Mozer et al. (1978). Ion streaming in a direction consistent with the Y-component of the drift velocity was observed whereas streaming along the X and Z-components is not seen. Based on energy arguments we conclude that in this case, 24 keV ions are not the major energy carrier of the locally measured · dissipation.     

Detectors for infrared heterodyne mixing and detection

Conclusion For wavelengths < 50m fast and sensitive detectors are available. For wavelengths > 50m the available detectors are far from ideal. Research and development of far infrared detectors for the mixing purpose are highly recommended.     

Anomalous Cosmic Rays and Solar Modulation

We review aspects of anomalous cosmic rays (ACRs) that bear on the solar modulation of energetic particles in the heliosphere. We show that the latitudinal and radial gradients of these particles exhibit a 22-year periodicity in concert with the reversal of the Sun's magnetic field. The power-law index of the low energy portion of the energy spectrum of ACRs at the shock in 1996 appears to be -1.3, suggesting that the strength of the solar wind termination shock at the helioequatorial plane is relatively weak, with s 2.8. The rigidity dependence of the perpendicular interplanetary mean free path in the outer heliosphere for particles with rigidities between 0.2 and 0.7 GV varies approximately as R2, where R is particle rigidity. There is evidence that ACR oxygen is primarily multiply charged above 20 MeV/nuc and primarily singly-charged below 16 MeV/nuc. The location of the termination shock was at 65 AU in 1987 and 85 AU in 1994.     

Voyager energetic particle observations at interplanetary shocks and upstream of planetary bow shocks: 1977–1990

The Voyager 1 and 2 spacecraft include instrumentation that makes comprehensive ion (E 28 keV) and electron (E 22 keV) measurements in several energy channels with good temporal, energy, and compositional resolution. Data collected over the past decade (1977–1988), including observations upstream and downstream of four planetary bow shocks (Earth, Jupiter, Saturn, Uranus) and numerous interplanetary shocks to 30 AU, are reviewed and analyzed in the context of the Fermi and shock drift acceleration (SDA) models. Principal findings upstream of planetary bow shocks include the simultaneous presence of ions and electrons, detection of tracer ions characteristic of the parent magnetosphere (O, S, O⁺), power-law energy spectra extending to 5 MeV, and large (up to 100:1) anisotropies. Results from interplanetary shocks include observation of acceleration to the highest energies ever seen in a shock ( 22 MeV for protons, 220 MeV for oxygen), the saturation in energy gain to 300 keV at quasi-parallel shocks, the observation of shock-accelerated relativistic electrons, and separation of high-energy (upstream) from low-energy (downstream) populations to within 1 particle gyroradius in a near-perpendicular shock. The overall results suggest that ions and electrons observed upstream of planetary bow shocks have their source inside the parent magnetosphere, with first order Fermi acceleration playing a secondary role at best. Further, that quasi-perpendicular interplanetary shocks accelerate ions and electrons most efficiently to high energies through the shock-drift process. These findings suggest that great care must be exercised in the application of concepts developed for heliosphere shocks to cosmic ray acceleration through shocks at supernova remnants.     

A New Mechanism of Coronal Heating

The interaction between network magnetic fields and emerging intranetwork fields may lead to magnetic reconnection and microflares, which generate fast shocks with an Alfvén Mach number M _A<2. Protons and less abundant ions in the solar corona are then heated and accelerated by fast shocks. Our study of shock heating shows that (a) the nearly nondeflection of ion motion across the shock ramp leads to a large perpendicular thermal velocity (v _th), which is an increasing function of the mass/charge ratio; (b) the heating by subcritical shocks with 1.1 M_A 1.5 leads to a large temperature anisotropy with T/T 50 for O⁵⁺ ions and a mild anisotropy with T_/T 1.2 for protons; (c) the large perpendicular thermal velocity of He⁺⁺ and O⁵⁺ ions can be converted to the radial outflow velocity (u) in the divergent coronal field lines; and (d) the heating and acceleration by shocks with 1.1 M_A 1.5 can lead to u(O⁵⁺) v _th(O⁵⁺) 460 km s^–1 for O⁵⁺ ions, u(He⁺⁺) v _th(He⁺⁺) 360 km s^–1 for He⁺⁺ ions, and u(H⁺) v _th(H⁺) 240 km s^–1 for protons at r=3–4 R . Our results can explain recent SOHO observations of the heating and acceleration of protons and heavier ions in the solar corona.     

The effect of rotation on the hydrodynamics of stellar collapse

Summary Using values of d, _min, and _max that Van Riper (1978) has found most promising for a hydrodynamic envelope ejection, we have shown that even a small amount of rotation in the initial core can stop its collapse before nuclear densities are reached. We expected _i > 0.02 to produce significant deviations from a spherically symmetric collapse, but have found that _i as much as ten times smaller than this will not allow the core to reach densities as high as in the spherical collapse. In no case, however, does the core flatten very much, nor does the value of become very large. Low final 's preclude the formation of an axisymmetric torus. They also indicate that deformation of an iron core into a triaxial configuration or fragmentation of the core during its collapse is an extremely unlikely event. (Note: Classically, must exceed 0.27 before a dynamic instability to non-axisymmetric perturbations is encountered.)The small degree of flattening of the core also suggests that the reduced moment of inertia I of the core will always be relatively small in magnitude and hence that the third time derivative of I, which is proportional to the energy emitted in gravity wave radiation, will not be very significant. Numerically calculated estimates of I- during some of these model evolutions supports this suspicion. If the _min and used here are found to be realistic values after the detailed physics of the core collapse is well understood, it is clear that gravitational radiation from a core collapse will be difficult to measure.Finally, we should point out that it is the relatively large values of Y_min (near 4/3) combined with values of d near unity that (a) prevented the core from flattening significantly in these models and (b) prevented the core from reaching high configurations. If realistic values of either one (or both) of these parameters are found to be much smaller in more complete models of the core collapse, then the core will have to become flatter (and denser) before pressure gradients will support it along the rotation axis. All of the conclusions drawn here would be modified accordingly under those circumstances. It should also be noted that in general relativistic models, the critical for spherical collapse is somewhat larger than 4/3 (Van Riper, 1979). Therefore, we predict that when fully general relativistic core collapses are performed including rotation, a given choice of _min and _i will produce a slightly flatter and slightly denser core than the corresponding model that has been presented here.     

CCD spectroscopy of the W Serpentis binaries KX And and RX Cas

Initial results are presented from a study of H profiles in the two interacting binaries KX And and RX Cas of W Serpentis type. The used CCD spectra with a resolution of 0.13Å/px were obtained with the 2.2m telescope and the Coudé spectrograph at the German-Spanish Astronomical Center at Calar Alto/Spain.KX And. This star is probably a non-eclipsing member of the W Serpentis type interactive binaries and has a period of P = 38.908 days. Our seven spectra of KX And were obtained at phase 0.54 – 0.75. The P Cyg profiles of the H line during our observations indicate an expanding shell. The asymetry becomes blue-sided at phase 0.67 and increases thereafter. This points toward a strong outflow of matter in the vicinity of the L3 point.RX Cas. According to the model of Andersen et al. (1988) the primary is a mid-B type star with M = 5.8M and R = 2.5R . The star is completely obscured by a geometrically and optically thick disk, which is supplied by mass transfer from the other component. The secondary is a K1 giant with M = 1.8M and R = 23.5R and fills out his critical Roche lobe. Radiative and geometrical properties of the disk are variable and its structure is probably not homogenous.Five spectra of RX Cas were obtained during the primary eclipse (phase 0.95 – 0.19). The observed double-peak emission is seen only after the eclipse with a separation of 250 km/s peak-to-peak, while during the eclipse an asymetric line profile can be observed with a red-shifted emission always presented. Also, a central emission at = 0.94 should be noticed, probably originating in the vicinity of L1.The observations of both systems indicate that we are dealing with strongly interacting binaries. Further observations are planned for better covering of phase.Visiting Astronomer, German-Spanish Astronomical Center, Calar Alto, operated by the Max-Planck-Institut für Astronomie Heidelberg jointly with the Spanish National Commision for Astronomy.     

The Edison infrared space observatory

For five years, theEdison program has had the goal of developing new designs for infrared space observatories which will break the cost curve by permitting more capable missions at lower cost. Most notably, this has produced a series of models for purely radiative and radiative/mechanical (hybrid) cooling which do not use cryogens and optical designs which are not constrained by the coolant tanks. Purely radiatively-cooled models achieve equilibrium temperatures as low as about 20 K at a distance of 1 AU from the sun. More advancedEdison designs include mechanical cooling systems attached to the telescope assembly which lower the optical system temperature to 5 K or less. Via these designs, near-cryogenic temperatures appear achievable without the limitations of cryogenic cooling. OneEdison model has been proposed to the European Space Agency as the next generation infrared space observatory and is presently under consideration as a candidate ESA Cornerstone mission. The basic design is also the starting point for elements of future infrared space interferometers.     

Large scale structure of the universe

The current situation with the cosmological model and fundamental constants is briefly reviewed. Here, we concentrate on evolutionary effects of large-scale structure formation, in particular, the relationship with the quasar distribution and dynamics is discussed. We argue that groups of bright quasars with few or more than dozen of members within regions l _LS(100–150)h ^–1 Mpc found atz<2 may belong to concentrations of young rich clusters of galaxies, and thus be distant Great Attractors like the local GA or the Shapley concentration. These early large-scale galactic structures (i) provide a natural way to bias the distribution of Abell clusters, and (ii) suggest that the spectrum of primordial density perturbations is nearly flat on scales encompassing both the cluster and GAs,l=k ^–1(10,100)h ^–1 Mpc: _k ² k ³ P(k) k , =1 _–0.4 ^+0.6 , whereP(k) is the power spectrum of density perturbations.     

Optical identification of X-ray sources in the Einstein observatory medium and deep surveys

Methods are discussed for establishing the optical identification of X ray sources in the medium and deep X-ray surveys of the Einstein Observatory. Of the 63 X-ray sources with a statistical significance of 5 in the medium survey (Maccacaro et al. 1981), optical identification work is summarized for 51, of which identifications have been made with 30 active galactic nuclei. The optical properties of some of these X-ray selected objects are briefly discussed.The Einstein deep survey of Pavo (Griffiths et al. 1981) is used to illustrate the problems and methods used for securing optical identifications for X-ray sources in the deep survey fields. Identifications have been made with 4 QSOs at the bright end of the optical candidate distribution (together with 3 G stars) and it is shown that a further 7 fainter objects are also likely to be QSOs.     

Starburst galaxies

Bursts of massive star formation can temporarily dominate the luminosity of galaxies spanning a wide range of morphological types. This review is concerned primarily with such events in the central 1 kpc region of spiral galaxies which result from bar driven inflows of gas triggered by interactions or mergers. Most of the stellar radiant luminosity of such bursts is absorbed by dust and re-emitted in the far-infrared and is accompanied by radio and X-ray emission from supernova remnants which can also act collectively to drive galaxy scale outflows. Both evolutionary stellar models and estimates of the gas depletion times are consistent with typical burst durations of 10^7–8 yr. Spatially-resolved studies of nearby starburst galaxies reveal that the activity is distributed over many individual star forming complexes within rings and other structures organized by interactions between bars and the disc over a range of scales. More distant and extreme examples associated with mergers of massive spirals have luminosities > 10¹³ L and molecular gas masses > 10¹⁰ M implying star formation rates > 1000 M yr^–1 which can only be sustained for 10⁷ yr. In the most luminous merging systems, however, the relative importance of starburst and AGN activity and their possible evolutionary connection is still a hotly debated issue. Also controversial are suggestions that starbursts in addition to a black hole are required to account for the properties of AGNs or that starbursts alone may be sufficient under certain conditions. In a wider context, starbursts must clearly have played an important role in galaxy formation and evolution at earlier times. Recent detections of high redshift galaxies show that star formation was underway at z 4 but do not support a continuing increase of the strong evolution in the co-moving star formation density seen out to z l. Primeval starburst pre-cursors of spheroidal systems also remain elusive. The most distant candidates are radio galaxies and quasars at z = 4–5 and a possible population of objects responsible for an isotropic sub-mm wave background tentatively claimed to have been detected by the COBE satellite.     

The gravity-darkening of the main-sequence components of spectral types A, F and G in detached close binary systems

From analysis of the photometric ellipticity effect in seven well-understood detached close binary systems, empirical values of the exponent of gravity-darkening have been practically deduced for eleven main-sequence components of spectral types A, F and G which should cover the range of structural change (from radiative to convective) in stellar atmospheres. The result indicate that values of the exponent diminish gradually with decreasing effective temperatures from 1.0 for radiative atmospheres with T > 8500 K to = 0.2 0.3 for convective atmospheres with T < 6500 K, in spite of some uncertainty in the reflection correction process.