α-particle observations in the solar wind

The plasma experiment on board of the ESRO satellite HEOS-1 detects solar wind positive ions in the energy range from 200 eV/Z–16000 eV/Z. -particles have been observed for 10% of the time, from December 1968 to March 1969, when in the interplanetary medium -particle and proton bulk velocities are on average equal. The average relative abundance of -particles is 5.5 %.Although in general the two species, hydrogen and helium, have a similar behaviour, very often -particles have an independent time history. Strong discontinuities may be observed in one species, without occurring in the other, or having different characteristics. At certain times, -particles seem to behave as an independent fluid.Well defined fluxes of -particles are observed within the magnetosheath: in several cases -particles, present in the unperturbed solar wind, are found with unchanged energy spectrum through a certain layer behind the proton shock front inside the magnetosheath. This suggests that thermalization of -particles does not occur at the same place as that of protons.     

Heating and acceleration of α-particles in the solar wind

The non-linear saturation of whistler mode instability in the solar wind is considered here. The resulting heating and acceleration are calculated. It is shown that this instability heats predominantly the -particles and the ratio of heating rates of -particles to ions have been calculated. This instability is shown to be effective in accelerating -particles than ions. However, this process cannot account for V /V _i 1.     

On the modeling of the three-fluid structure of the quiet solar wind

The reciprocal influence of the electrons and protons, on one side, and the -particles, on the other side in the quiet solar wind is investigated within the framework of a conductive three-fluid model (with frictional forces included). For this purpose two mathematical methods are used, namely: I. Simultaneous solution of the fluid equations for all three species; and II. Solution of two-fluid equations (for electrons and protons) followed by that of a modified one-fluid equation for the -particles (in which the two-fluid solutions are used for electrons and protons).The results of our investigation indicate the following: (a)The macroscopic -particle characteristics as obtained from the two methods of solution are almost identical. Thus, the differences between the three-fluid and two-fluid characteristics of the electrons and protons represent a second order (and negligible) effect on the -particle characteristics. In both approaches, the frictional interaction between -particles and protons raises the (lower) -particle streaming velocity to that of the protons and decreases the relative to proton density ratio to a value about 0.035, as observed at 1 AU, (b)The electron and proton characteristics obtained from three-fluid and two-fluid solutions are similar, except for the proton temperature. The two-fluid solution providesT _p-values which, though within the observational error, are larger than those obtained from the simultaneous three-fluid solution (at 1 AU, the difference amounts to about 30%). Thus, the -particles affect the temperature profile of the protons in the solar wind through heat exchange (mainly), dynamical friction, as well as through their contribution to the interplanetary electrostatic field.     

Linearly expanding universes in JBD-theory

The assumption of a linearly expanding universe for the JBD-cosmological equations generates a set of solutions for the barotropic equations of statep= (=const.). These solutions turn out to be valid for closed space-except in the casep= which is for open space. The gravitational constant which is inversely proportional to the scalar field increases with time if >–1/3 and decreases for <–1/3. No solution exists for =1/3. The Brans-Dicke parameter is negative if <–1/3.     

In situ acceleration and gradients of charged particles in the outer solar system observed by the voyager spacecraft

The probable connection between cosmic rays and the electromagnetic state of the interplanetary medium was recognized by Hannes Alfvén as early as 1949 (Alfvén, 1949, 1950); he pointed out that the properties of cosmic rays necessitate a mechanism, external to Earth but within the solar system, capable of accelerating particles to extremely high energies. In advocating the view of local origin for part of the cosmic-ray spectrum, Alfvén and his colleagues developed a very general type of acceleration mechanism called magnetic pumping. The unique data set of the two Voyagers extends over an entire decade (1977–1987) and is most suitable to explore the problem of acceleration of charged particles in the heliosphere. The energy coverage of the Low Energy Charged Particle (LECP) experiment covers the range 30 keV to several hundred MeV for ions and 22 keV to several MeV for electrons. Selected observations of interplanetary acceleration events from 1 to 25 AU are presented and reviewed. These show frequent acceleration of ions to several tens of MeV in association with shocks; highest energies (220 MeV oxygen) were measured in the near-perpendicular ( _Bn 87.5°) shock of January 5, 1978 at 1.9 AU, where electron acceleration was also observed. Examples of ion acceleration in association with corotating interaction regions are presented and discussed. It is shown that shock structures have profound effects on high-energy (70 MeV) cosmic rays, especially during solar minimum, when a negative latitudinal gradient was observed after early 1985 at all energies from 70 MeV down to 30 keV. By early 1987, most shock acceleration activity in the outer heliosphere (25 to 30 AU) had ceased both in the ecliptic (Voyager-2) and at higher (30°) ecliptic latitudes (Voyager-1). The totality of observations demonstrate that local acceleration to a few hundred MeV, and as high as a few GeV is continually present throughout the heliosphere. It should be noted that in 1954 when Alfvén suggested local acceleration and containment of cosmic rays within the solar system, no one treated his suggestion seriously, at any energy. The observations reviewed in this paper illustrate once more Alfvén's remarkable prescience and demonstrate how unwise it is to dismiss his ideas.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.     

High-resolution photography of the solar chromosphere

A method is described for reconstructing the true geometry of a solar loop observed on the disk which takes account of tilt in its own plane. Reconstructions of three H loops yield small tilt angles (14°) and provide further evidence that H loops show a close correspondence to the field lines of a magnetic dipole. The method offers new opportunities for exploring the physics of individual solar loops.     

The solar filigree

As a birefringent filter is tuned from the center of H to the continuum the H bright mottles appear to break up into a network of grains. The name filigree is suggested for this bright network. Its size, shape, contrast and time evolution is described as well as its relation to the abnormal granulation, magnetic field and spicules.On leave from The University of Hawaii.     

The solar-flare infrared continuum: Observational techniques and upper limits

Exploratory observations at 20 and 350 have determined detection thresholds for solar flares in these wavelengths. In the 20 range solar atmospheric fluctuations (the temperature field) set the basic limits on flare detectability at 5K; at 350 the extinction in the Earth's atmosphere provides the basic limitation of 30K. These thresholds are low enough for the successful detection of several infrared-emitting components of large flares. Limited observing time and lack of solar activity have prevented observations of large flares up to the present, but the techniques promise to be extremely useful in the future.The upper limits obtained thus far, for subflares, indicate that the thickness of the H flare region does not exceed 10 km. This result confirms the conclusion of Suemoto and Hiei (1959) regarding the small effective thickness of the H-emitting regions in solar flares.     

Non-thermal solar wind heating by supra-thermal ions

The effect of a new energy source due to energies transferred from supra-thermal secondary ions on the temperature profile of the solar wind has been considered. For this purpose a solution of a tri-fluid model of the solar wind including solar electrons, protons, and -particles, and starting with the boundary conditions of Hartle and Barnes at 0.5 AU is given. On the base of the assumption that suprathermal He⁺-ions which have four times the temperature of suprathermal protons are predominantly coupled to solar -particles by Alfvén waves, it is shown that the temperature T of solar -particles should be appreciably higher than those T _p of solar protons beyond the orbit of the Earth. For 1 AU a temperature excess T over T _p according to that which has been found in some solar wind ion spectrograms can only be explained for a small part of the orbit of the earth which is inside the cone of enhanced helium densities. Around 1 AU the temperatures T and T _p are found to decrease much slighter with solar distance than given in the two-fluid model of Hartle and Barnes. Beyond 1.7 and 2.2 AU the temperatures T and T _p even start increasing with solar distance and come up to about 10⁵ at about 10 AU. These predictions should lend some support to future temperature measurements with deep-space probes reaching Solar distances of some AU.Forschungsberichte des Astronomischen Institutes, Bonn, 72-10.     

Kα line emission during solar X-ray bursts

K X-ray line emission from S, Ar, Ca and Fe is calculated for conditions likely to exist in solar flares. We consider both the non-thermal and thermal phases of flares as indicated by X-ray observations. Impulsive non-thermal events seen at the onset of a flare at photon energies > 20 keV generally give rise to small K line fluxes (<250 photons cm^-2 s^-1) on the basis of data presented by Kane and Anderson. The amount of S K radiation in particular depends sensitively on the lower-energy bound of the non-thermal electron distribution giving rise to the impulsive burst, offering a possible means of determining this. Thermal K emission is significant for only Fe ions. For S, Ar and Ca, the temperatures required for a sizeable number of electrons with energies greater than the K-ionization potential will also strip these elements to ionization stages too high for K transitions to be possible. Comparison of thermal K emission from iron during an intense solar flare leads to a very high emission measure on the basis of these calculations, but such a value seems to be compatible with an analysis of the 1–3 Å continuum during the same event.NAS/NRC Resident Research Associate.Visiting Scientist, High Altitude Observatory, NCAR, Boulder, Colo. 80302.     

An Estimate of Microwave low-Brightness-Temperature Regions' Heights Obtained Measuring Their Rotation Velocity

Daily full-disk solar maps obtained at 37 GHz in the years 1979, 1980, 1981, 1982, 1987, 1988, 1989, 1990, and 1991 are analysed and compared with full-disk solar maps in H. A search for a difference in the measured angular rotation velocity for two classes of microwave low-brightness-temperature regions (LTRs), associated and not associated with H filaments, is performed. Procedures with and without statistical weights, assigned to angular rotation velocities according to the tracing time, are applied and the statistical significance of the results is discussed. A higher angular rotation velocity is measured for LTRs associated with H filaments than for the not-associated ones. This angular velocity difference is interpreted as a consequence of a height difference between these two types of LTR tracers. Changes of the solar differential rotation velocity during the activity cycle measured using LTRs as tracers are explained by the measured cycle-dependence of the association rate between LTRs and H filaments. Similarly, the north–south asymmetry in the solar rotation velocity measured tracing LTRs is explained by the measured north–south asymmetry in the association rate between LTRs and H filaments. The rotation velocity of LTRs and H filaments is on the average more rigid in comparison with sunspots.     

On the line intensity ratios E(Hα)/E(D3) and E(Hβ)/E(D3) in prominences

The intensity ratios E(H)/E(D3) and E(H)/E(D3) in prominences depend on the total optical thickness in H of the layer. The emission of the He D3 line appears relatively enhanced in thin layers and in outer parts of the prominences.     

The spectra of extended radio sources with a nonuniform magnetic field and hard injection of particles

On the basis of an analytical solution of the diffusion-type kinetic equation for electrons, electron distributions and radiation spectra have been found which result from a hard injection of particles in sources of the core halo type, characterized by spatially nonuniform magnetic fields and diffusion parameters. Such radio sources are shown to possess nonlinear radiation spectra containing universal (=0.5) and diffusion-controlled power-law sections shaped by synchrotron losses, spatial diffusion and radiation conditions of the electrons. The diffusion-controlled sections can be described by spectral indices 0.5<1, if the magnetic field decreases towards the source edge, and by <0.5 where the magnetic field increases.     

Theory of the Trojan asteroids,IV

In a previous publication (1977) the author has constructed a family () of long-periodic orbits in the Trojan case of the restricted problems of three bodies. Here he constructs the domain of the analytical solution of the problem of the motion, excluding the vicinity of thecritical divisor which vanishes at the exact commensurability of the natural frequencies ₁ and ₂. In terms of thecritical masses m_j(₂), or the associatedcritical energies _j ² (m), is the intersection of the intervals ofshallow resonance, of the form. Inasmuch as the intervals |₂– _j ² |<_j ofdeep resonance aredisjoint, it follows that (1) the disjointed family () embraces the tadpole branch, 0²1, lying in: and (2) despite the clustering of _j ² (m) atj=, the family () includes, for ²=1, an asymptoticseparatrix that terminates the branch in the vicinity of the Lagrangian pointL ₃.In a similar manner, the family () can be extended to the horseshoe branch 1<_{2 2} ² .     

Lyman continuum observations of solar flares

A study is made of Lyman continuum observations of solar flares, using data obtained by the Harvard College Observatory EUV spectroheliometer on the Apollo Telescope Mount. We find that there are two main types of flare regions: an overall mean flare coincident with the H flare region, and transient Lyman continuum kernels which can be identified with the H and X-ray kernels observed by other authors. It is found that the ground level hydrogen population in flares is closer to LTE than in the quiet Sun and active regions, and that the level of Lyman continuum formation is lowered in the atmosphere from a mass column density m 5/sx 10^–6 g cm^–2 in the quiet Sun to m 3/sx 10^–4 g cm^–2 in the mean flare, and to m 10^–3g cm^–2 in kernels. From these results we derive the amount of chromospheric material evaporated into the high temperature region, which is found to be - 10¹⁵g, in agreement with observations of X-ray emission measures. A comparison is made between kernel observations and the theoretical predictions made by model heating calculations, available in the literature; significant discrepancies are found between observation and current particle-heating models.     

The behaviour of the infrared lines of neutral oxygen and the balmer lines of hydrogen in the spectra of early-type stars with emission lines

The equivalent widths of the oxygen lines at 7774 and 8446 and of H (and some H) have been measured for 22 early-type, emission-line stars. A strong correlation between H and 8446 intensities has been found, although there is no such correlation between H and 7774. This confirms the probability that Bowen's mechanism is operative (the neutral oxygen 3³ D state is overpopulated because the excitation energy of Ly- nearly coincides with that of theOi 1025 line). The possibility of using 8446 and H equivalent widths for a comparison of oxygen to hydrogen abundances in these stars is discussed.     

Observations of Ellerman bombs in H α

A developing active region near the center of the solar disk was observed for 80 min at the center and the wings of H. Ellerman bombs lying both below an Arch Filament System and near sunspots were studied at H - 1.0 Å and H - 0.75 Å. We determined their average contrast, lifetime, size and we studied their flux as a function of time. We found evidence that the size of Ellerman bombs increases with height. The time curves of flux provide evidence for both impulsive and gradual energy release. Under the AFS the Ellerman bombs form a cellular pattern with a characteristic size of 3.1 × 10³ km. Fifty percent of the bombs appear and disappear in pairs, possibly associated with bipolar emerging magnetic flux tubes.     

On the sun's pole-equator flux differences

We study the possibility that large flux differences between the poles and the equator at the bottom of the solar convective zone are compatible with the small differences observed at the surface. The consequences of increasing the depth of the convective zone due to overshooting are explored.A Boussinesq model is used for the convective zone and we assume that the interaction of the global convection with rotation is modelled through a convective flux coefficient whose perturbed part is proportional to the local Taylor number. The numerical integration of the equations of motion and energy shows that coexistence between large pole-equator flux differences at the bottom and small ones at the surface is possible if the solar convective zone extends to a depth of 0.4R . The angular velocity distribution inside the convective zone is in agreement with the -dynamo theories of the solar cycle.     

Numerical stabilization of Keplerian motion

The time transformation dt/ds=r is studied in detail and numerically stablized differential equations are obtained for =1,2, and 3/2. The case =1 corresponds to Baumgarte's results.     

The activity of stellar aggregates and the origin of cosmic rays

A concept of stellar aggregate activity is advanced. It is shown that the aggregate activity is too high in order to generate cosmic rays. Two conditions lay claim to cosmic ray primary sources: (i) a very large number of sources (10⁴), and (ii) a homogeneous distribution of sources in the Galaxy. Supernovae do not satisfy both those conditions, but stellar aggregates do. The total interstellar medium of the aggregate identifies with a supernova remnant and possesses properties favourable for the acceleration of cosmic rays up to a high energy by statistical mechanisms. The direct suppliers of primary cosmic rays are the flare stars in the aggregates. From the point of view of energetic resources as well as the energetic consistency of cosmic rays, aggregates are equivalent with supernova remmants. The aggregate must also be the source of gamma-rays. The usual UV Cet-type flare stars in the Sun's neighbourhood do not play any role as sources of primary cosmic rays.The aggregate conception connects the very fact of the existence of cosmic rays with the continued star-formation process in Galaxy.