Ariel-6 medium energy spectral observations of active galaxies

X-ray spectra of the BL Lac type object Mkn 421 and several Seyfert type 1 galaxies; IIIZw2, MCG8-11-11 and NGC 4151, have been obtained using the Leicester University instrument on board the Ariel-6 satellite. The Mkn 421 spectrum is best represented by two powerlaw components, the soft component having 3.4 whilst the hard flux has 1.0. In MCG8-11-11 there is clear evidence for spectral variability between our observation in late 1979 and that of HEAO-1/A2 in 1977. The Ariel-6 spectrum of MCG8-11-11 can be fitted by a powerlaw of index 2.1 together with an iron line at 6.2 keV with an equivalent width of 1.6 keV. The first X-ray spectrum of IIIZw2 is also presented, fitting with a powerlaw we find an index of 1.7. With the exception of NGC 4151 there is no evidence for a significant column of cool material along the line of sight.     

High-resolution observations of Hα flare regions

This paper gives a review of the recent high-resolution H observations of solar flares and flare-productive active regions. From studies of the morphological and evolutional features of H flare emitting regions, two types of two-ribbon flares, which are termed separating two-ribbon flare and confined two-ribbon flare, are discussed. The former is characterized by conspicuous separating motions or expanding motions of the H two ribbons, whereas the latter shows only a short range of or no separating motions of the two ribbons. The explosive compact flares, which occur in some compact newly-emerging flux regions, are also discussed.Attention is paid to the successive and impulsive brightenings of H flare points which form the H flare kernels and the front lines of H two ribbons at the impulsive phases of flares. Temporal relationships between H line intensities or profiles and hard X-ray or microwave emissions are discussed to discriminate the energy transport mechanisms in the flare loops.H monochromatic image of high spatial resolution, at the present time, is the most sensitive detector for finding the first appearance of newly-emerging magnetic flux region and the developing features of sheared configuration of magnetic field, both of which are the key factors in flare energy build-up processes. It is suggested that the successive emergence of a twisted magnetic flux rope might be essential for the production of a major flare.Contributions from the Kwasan and Hida Observatories, Kyoto University, No. 292.     

The astrophysical interest of EUV observations of extra-solar objects

The feasibility of observation of EUV sources is assessed. Many stars have been detected in the EUV range ( 100–1000); line fluxes from others can be predicted. Selected astrophysical problems are reviewed that can benefit from EUV spectroscopy. Included among them are the physics and dynamics of stellar coronae, confirmation of nuclear surface burning on cataclysmic variables, evolutionary properties of white dwarfs, the helium abundance in the interstellar medium, and spectroscopic signatures of neutrino oscillations.Proceedings of the Conference Solar Physics from Space, held at the Swiss Federal Institute of Technology Zurich (ETHZ), 11–14 November 1980.     

Gamma-ray line production in astronomical objects

This review focuses on the conditions for -ray line production in the most interesting astronomical objects, in light of the planned experiments: Gamma-1, GRO, Sigma, GRASP, and others. Among these objects are the Sun, the galactic center region, molecular and dust clouds, accreting and exploding stars.     

Observed Densities in the Universe

Baryons observed in Ly absorbers contribute to the density parameter 0 by bar 0.06 in close agreement with the value of 0.06 from primordial nucleosynthesis (H0=55 km s-1 Mpc-1, = 0 assumed throughout). A number of methods are known to measure 0 from density fluctuations; bound structures tend to yield lower values (m 0.2-0.4), field galaxies over large scales higher, but still undercritical values (m 0.6 ± 0.2). The best compromise value is 0 0.5, but the present methods are blind to diffusely distributed, exotic matter which still could make 0 = 1. A satisfactory solution of 0 (and ) will only come from a fundamental cosmological test (e.g. the Hubble diagram of [evolution-corrected] supernovae type Ia) in combination with the CMB fluctuation spectrum.     

Gamma Rays From Molecular Clouds

High energy -rays from individual giant molecular clouds contain unique information about the hidden sites of acceleration of galactic cosmic rays, and provide a feasible method for study of propagation of cosmic rays in the galactic disk on scales 100 pc. I discuss the spectral features of ⁰-decay -radiation from clouds/targets located in proximity of relatively young proton accelerators, and speculate that such `accelerator+target systems in our Galaxy can be responsible for a subset of unidentified EGRET sources. Also, I argue that the recent observations of high energy -rays from the Orion complex contain evidence that the level of the `sea of galactic cosmic rays may differ significantly from the flux and the spectrum of local (directly detected) particles.     

Non-BBN Constraints on the Key Cosmological Parameters

Since the baryon-to-photon ratio 10 is in some doubt at present, we ignore the constraints on 10 from big bang nucleosynthesis (BBN) and fit the three key cosmological parameters (h, M, 10) to four other observational constraints: Hubble parameter (ho), age of the universe (to), cluster gas (baryon) fraction (fo fGh3/2), and effective shape parameter (o). We consider open and flat CDM models and flat CDM models, testing goodness of fit and drawing confidence regions by the 2 method. CDM models with M = 1 (SCDM models) are accepted only because we allow a large error on ho, permitting h < 0.5. Open CDM models are accepted only for _M 0.4. CDM models give similar results. In all of these models, large 10 ( 6) is favored strongly over small 10 ( 2), supporting reports of low deuterium abundances on some QSO lines of sight, and suggesting that observational determinations of primordial 4He may be contaminated by systematic errors. Only if we drop the crucial o constraint are much lower values of M and 10 permitted.     

Nonlinear theory of the two-point correlation function

We consider the influence of the nonlinear stage of gravitational instability on the two-point correlation functions of gravitationally bound objects. Based on the theory of nonlinear gravitational contraction of a single density peak of dissipationless matter (Gurevich and Zybin, 1988a,b; 1990) we develop a method for calculating the two-point correlation functions of different objects of any mass. The method works good in the region of strong correlations and can be easily extended to calculate higher correlation functions. We show that the main contribution to the correlation function _i in the region of strong correlations _i 1 is made by pair systems located outside large clusters of objects. In this region the shape of _i is determined only by the nonlinear dynamics of gravitational contraction of dissipationless matter and has the form _i C ^–, where 1.8 is a universal parameter.     

Concerning the interpretation of the ultraviolet radiation from B stars

Measurements of the shape of the ultraviolet spectrum from B stars are compared with the theoretical spectra predicted from a homogeneous series of eight model atmospheres which are known to be close to a state of radiative equilibrium and to give a good representation of the ordinarily observed spectral region. The broad-band photometer measurements of Byram, Chubb, and Friedman in the region 1314 indicate that the stars become brighter in the ultraviolet as their temperature increases. The theoretical spectra reproduce this trend. However, the theoretical spectra are about three times as bright at 1314 relative to their brightness at 5560 as is observed.The spectral observations at 50Å resolution of Stecher and Milligan of six absorption-line stars are compared in detail with theoretical spectra. The observed shape of the spectrum is reproduced well by the models from 2600 to longer wavelengths. At wavelengths shorter than 2600 Å, the observed fluxes from B stars are less than the predicted fluxes. At 2000 the deficiency is between a factor two and a factor four. The spectrum of Canis Majoris is observed to have a different shape from that found for four other early-type stars. In the case of Canis Majoris the deficiency at 2000 is about a factor 13.The proper manner in which to compare theory and observation is discussed and some astrophysical terminology is explained. Theoretical fluxes, , are given in Table 1 for eight early B type model atmospheres at wavelengths between the Lyman limit and 6251. These fluxes have been computed without consideration of the opacity due to line blanketing. It is shown that line blanketing can probably account for the differences noted between predicted and observed ultra-violet spectra of B stars. It is not necessary at present to invoke unusual sources of opacity in the stellar atmosphere or in the space between the star and the earth in order to explain the observations. Spectra of B stars in the 2000 region at sufficient resolution to show the line spectrum would clarify the problem.     

Plasma waves at the dayside magnetopause

Experimental investigations of plasma waves at the magnetopause, including recent results from the AMPTE/IRM satellite, show that both E and B fluctuations typically have a featureless spectrum which monotonically decreases with frequency; integrated rms amplitudes are typically a few mV m^-1 for E and 10 nT for B, though in particular E can be as much as an order of magnitude larger in exceptional cases. Surveys show a lack of correlation between wave parameters and the magnetopause parameters. Under the assumption that crossing the diffusion region would give a pronounced signature in the waves, the survey data allow an upper limit to be placed on the latitudinal extent of the diffusion region, which is about 1000 km — implying that it is not surprising that the wave data surveys have so far failed to detect it. The observed wave turbulence levels have been used to estimate diffusion coefficients under different assumptions for the wave mode, but the resulting diffusion coefficient is always too small to explain either reconnection or boundary layer formation. Recent work of Galeev et al. (1986) indicates that the dominant diffusion process may be magnetic field migration, which is a macroscopic process involving the interaction of tearing mode islands. Assuming this mode to be present at the observed level of B, a particle diffusion coefficient of nearly 10⁹ m² s^-1 is obtained. Another macroscopic diffusive process which could occur at the magnetopause is stochastic E × B scattering, which also implies a diffusion coefficient the order of 10⁹ m² s^-1 if the observed E spectrum is assumed to be a turbulent cascade consisting of convective cells.     

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.     

Primordial Helium and ΔY/ΔZ from H II Regions and from Fine Structure in the Main Sequence Based on Hipparcos Parallaxes

The primordial helium abundance YP is important for cosmology and the ratio Y/Z of the changes relative to primordial abundances constrains models of stellar evolution. While the most accurate estimates of YP come from emission lines in extragalactic H II regions, they involve an extrapolation to zero metallicity which itself is closely tied up with the slope Y/Z. Recently certain systematic effects have come to light in this exercise which make it useful to have an independent estimate of Y/Z from fine structure in the main sequence of nearby stars. We derive such an estimate from Hipparcos data for stars with Z Z and find values between 2 and 3, which are consistent with stellar models, but still have a large uncertainty.     

SWE,a comprehensive plasma instrument for the WIND spacecraft

The Solar Wind Experiment (SWE) on the WIND spacecraft is a comprehensive, integrated set of sensors which is designed to investigate outstanding problems in solar wind physics. It consists of two Faraday cup (FC) sensors; a vector electron and ion spectrometer (VEIS); a strahl sensor, which is especially configured to study the electron strahl close to the magnetic field direction; and an on-board calibration system. The energy/charge range of the Faraday cups is 150 V to 8 kV, and that of the VEIS is 7 V to 24.8 kV. The time resolution depends on the operational mode used, but can be of the order of a few seconds for 3-D measurements. Key parameters which broadly characterize the solar wind positive ion velocity distribution function will be made available rapidly from the GGS Central Data Handling Facility.     

Probing the solar wind acceleration region using spectroscopic techniques

Measurements of the intensities and profiles of UV and EUV spectral lines can provide a powerful tool for probing the physical conditions in the solar corona out to 8 R and beyond. We discuss here how measurements of spectral line radiation in conjunction with measurements of the white light K-corona can provide information on electron, proton and ion temperatures and velocity distribution functions; densities; chemical abundances and mass flow velocities. Because of the fundamental importance of such information, we provide a comprehensive review of the formation of coronal resonance line radiation, with particular emphasis on the H i L line, and discuss observational considerations such as requirements for rejection of stray light and effects of emission from the geocorona and interplanetary dust. Finally, we summarize some results of coronal H i L and white light observations acquired on sounding rocket flights.Paper presented at the IX-th Lindau Workshop The Source Region of the Solar Wind.     

The magnetogram inversion technique: Applications to the problem of magnetospheric substorms

The magnetogram inversion technique (MIT) is based upon recordings of geomagnetic variations at the worldwide network of ground-based magnetometers. MIT ensures a calculation of a global spatial distribution of the electric field, currents and Joule heating in the ionosphere. Variant MIT-2 provides, additionally, continuous monitoring of the following parameters: Poynting vector flux from the solar wind into the magnetosphere (); power, both dissipated and accumulated in the magnetosphere; magnetic flux in the open tail; and the magnetotail length (l _T) (distance between the dayside and nightside neutral points in the Dungey model). Using MIT-2 and data of direct measurements in the solar wind, an analysis is made of a number of substorms, and a new scenario of substorms is suggested. The scenario includes the convection model, the model with a neutral line and the model of magnetosphere-ionosphere coupling (outside the current sheet), i.e., the three known models. A brief review is given of these and some other substorms models. A new element in the scenario is the strong positive feedback in the primary generator circuit, which ensures growth of the ratio = / _Aby an order of magnitude or more during the substorms. Here _Ais the Pointing vector flux in the Akasofu-Perrault approximation, i.e., without the feedback taken into account. The growth of during the substorm is caused only by the feedback effect. It is assumed that the feedback arises due to an elongation of the magnetotail, i.e., a growth of l _Tby a factor of (23) during the substorm.In the active phase of substorm, a part (the first active phase) has been identified, where the principal role in the energetics is played by the feedback mechanism and the external energy source (although the internal source plus reconnection inside the plasma sheet make a marked contribution). In the second active phase (expansion) the external generator (solar wind) is switched off, and the main role is now played by the internal energy source (the tail magnetic field and ionospheric wind energy).Models of DP-2 DP-1 transitions are also considered, as well as the magnetospheric substorm-solar flare analogy.     

The solar grazing incidence (GRIST) and optical (SOT) telescopes joint accommodation

Some of the problems foreseen for the joint accommodation and operation of the Grazing Incidence Solar Telescope (GRIST) under study by ESA to operate in the extreme ultraviolet region (90 < < 1700 Å), and the Solar Optical Telescope (SOT), developed by NASA to operate in the ultraviolet, optical and infrared region (A > 1100 Å) on a Spacelab mission are described.Proceedings of the Conference Solar Physics from Space, held at the Swiss Federal Institute of Technology Zurich (ETHZ), 11–14 November 1980.     

A dissection of 30 Doradus and a discussion of other Magellanic Cloud OB associations

I Present the results of ground-based and Hubble Space Telescope photometry and spectroscopy of the stars in the central region (roughly 7×7 arcmin) of 30 Doradus in the Large Magellanic Cloud (LMC). Using photometric data for over 2400 stars (complete toV18 mag), and spectroscopic observations of over 150 stars in the region, the best estimate of the initial mass function (IMF) yields a slope of =–1.5±0.2 for masses > 12M, where the Salpeter slope is =–1.35. I compare these results to other measurements of the IMF for OB associations in the Magellanic Clouds.     

Magnetograph based on magneto-optical effects

Simple and low-cost instruments, reduced in dimensions and, possibly, weight, are always welcome and very convenient, when they are intended for space applications.Proceedings of the Conference Solar Physics from Space, held at the Swiss Federal Institute of Technology Zurich (ETHZ), 11–14 November 1980.     

Presupernova models and supernovae

Present status of the theories for presupernova evolution and triggering mechanisms of supernova explosions are summarized and discussed from the standpoint of the theory of stellar structure and evolution. It is not intended to collect every detail of numerical results thus far obtained, but to extract physically clear-cut understanding from complexities of the numerical stellar models. For this purpose the evolution of stellar cores is discussed in a generalized fashion. The following types of the supernova explosions are discussed. The carbon deflagration supernova of intermediate mass star which results in the total disruption of the star. Massive star evolves into a supernova triggered by photo-dissociation of iron nuclei which results in a formation of a neutron star or a black hole depending on its mass. These two are typical types of the sueprnovae. Between them there remains a range of mass for which collapse of the stellar core is triggered by electron captures, which has been recently shown to leave a neutron star despite oxygen deflagration competing with the electron captures. Also discussed are combustion and detonation of helium or carbon which take place in accreting white dwarfs, and the collapse which is triggered by electron-pair creation in very massive stars.Appendix: Notations A mass number of atomic nucleus - B _v(a, b) incomplete beta function - c _p specific heat at constant pressure - c _p sound velocity - c(sub) center of the star - E _e mean energy of an electron captured by nucleus - E _n nuclear energy release from unit mass of the nuclear fuel specified by n - E _thr threshold energy (9.3) - E _thr,0 energy difference between the ground states of daughter nucleus and parent nucleus (9.1) - E energy of gamma ray emitted from daughter nucleus (9.1) - E _v mean energy of a neutrino emitted by electron capture (9.1) - f flatness parameter (2.17) - g local gravitational acceleration (2.16) - H atomic mass unit - H _p scale height of pressure (2.22) - H (sub) hydrogen-burning shell - k Boltzmann constant - l mixing length of convection - L _cr(M _r ) local Eddington's critical luminosity (4.3) - L _n integrated nuclear energy generation rate by nuclear fuel specified by n - L _v neutrino luminosity - L _{v, cr}(M _r ) local Eddington's critical neutrino luminosity (11.2) - M (current) mass of a star - m _M core mass contained interior to the carbon-burning shell - M _Ch Chandrasekhar's limiting mass (9.6) - M _H core mass contained interior to the hydrogen-burning shell - M _He core mass contained interior to the helium-burning shell - M _ms mass of a star at its zero-age min-sequence - M _O core mass contained interior to the oxygen-burning shell - M _r mass contained interior to a shell at r - M _Si core mass contained interior to the silicon-burning shell - M _WD mass of white dwarf (7.1) - M ₀ normalization factor to the non-dimensional mass (3.3) - M ₁ core mass (3.6) - N polytropic index between pressure and density (2.3) - n polytropic index between pressure and temperature (10.1) - N _A Avogadro number - N _ad adiabatic polytropic index - N _e number of electrons in unit mass of matter - NSE nuclear statistical equilibrium - P pressure - ph (sub) photosphere - Q _e mass fraction of the envelope exterior of the shell e (2.14) - R stellar radius - r radial distance of a shell - r ₀ normalization factor to the non-dimensional radius (3.2) - s specific entropy - S _i specific entropy of ions - T temperature - U homology invariant defined by (2.1) - u _gas specific internal energy of gas - u _rad energy of the radiation field per volume in which unit mass of gas is contained (6.4) - V homology invariant defined by (2.2) - _def velocity of deflagration front (6.10) - X concentration by weight of hydrogen - Y concentration by weight of helium - Y _e mole number of electrons in one gram of matter (9.7) - Y _v mole number of neutrinos in one gram of matter - Z concentration by weight of the elements other than hydrogen and helium - z shock strength (6.6) - 1 (sub) usually denotes the core edge (2.13) - ratio of the mixing length to the scale height of pressure (l/H _p ) - ratio of gas pressure to the total pressure - ratio of the specific heats - gD locus of singularity in U-V plane (2.5) - M(H _p ) mass contained within unit scale height of pressure (4.4) - _ec energy rate by electron captures (9.5) - _n nuclear energy generation rate by the nuclear fuel specified by n - _v neutrino loss rate - L _v ^(D) neutrino loss rate excluding the neutrinos from the electron captures (9.4) - non-dimensional density (3.1) - P/, not the non-dimensional temperature (2.7) - _W Weinberg's angle (5.8) - opacity - _v neutrino opacity (11.2) - describes the effect of electron degeneracy in equation of state (2.19) - _ec rate of electron capture - mean molecular weight - _e mean molecular weight of electrons - _e chemical potential of an electron excluding the rest mass (8.1) - _i mean molecular weight of ions - non-dimensional radius (3.1) - non-dimensional pressure (3.1) - matter density - _cr ^GR critical density above which the general relativistic instability sets in - _cr critical density for reimplosion of the core by beta processes (Section 5) - _ign density at the ignition - _nse density above which the deflagrated matter results in NSE composition - _e non-dimensional entropy of electron-per one electron in units of k(9.2) - _ff timescale of free fall (6.2) - _h (H _p ) timescale of heat transport over unit scale height of pressure (4.4) - _n nuclear timescale for a change in temperature (6.1) - non-dimensional mass (3.1) - _e chemical potential of an electron in units of kT (8.1)     

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.