Motions in arch filament systems

A new analysis of H filtergrams and H spectra of arch filament systems (AFS) shows that material flows downwards in both branches of the arch filaments (v 50 km/sec) while the top of the arches ascends (v 10 km/sec). It is suggested that AFS are produced by the magnetic field which expands, between growing spots, into higher levels carrying material with it that subsequently slides down along the magnetic field following gravity.AFS are also visible in the K line of Caii; however, there they appear less pronounced than in H and they are less conspicuous than the K-line quiescent filaments. There is some indication that AFS just cover a supergranulum (Ca network cell) with material streaming down at the border of the cell.No indication was found for a close relationship between AFS and flares.Mitteilung aus dem Fraunhofer Institut Nr. 91.     

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.     

Flaring arches

Flaring arches is a name assigned to a particular component of some flares. This component consists of X-ray and H emission which traverses a coronal arch from one to the other of its chromospheric footpoints. The primary footpoint is at the site of a flare. The secondary footpoint, tens of thousands of kilometers distant from the source flare, but in the same active region, brightens in H concurrent with the beginning of the hard X-ray burst at the primary site. From the inferred travel time of the initial exciting agent we deduce that high speed electron streams travelling through the arch must be the source of the initial excitation at the secondary footpoint. Subsequently, a more slowly moving agent gradually enhances the arch first in X-rays and subsequently in H, starting at the primary footpoint and propagating along the arch trajectory. The plasma flow in H shows clearly that material is injected into the arch from the site of the primary footpoint and later on, at least in some events, a part of it is also falling back.Thus a typical flaring arch has three, and perhaps four consecutive phases: (1) An early phase characterized by the onset of hard X-ray burst and brightening of the secondary footpoint in H. (2) The main X-ray phase, during which X-ray emission propagates through the arch. (3) The main H phase, during which H emitting material propagates through the arch. And (4) an aftermath phase when some parts of the ejected material seem to flow in the reverse direction towards the primary site of injection.An extensive series of flaring arches was observed from 6 to 13 November, 1980 at the Big Bear Solar Observatory and with the Hard X-Ray Imaging Spectrometer (HXIS) on board the SMM in a magnetically complex active region. The two most intense arches for which complete H and X-ray data are available and which occurred on 6 November at 17 21 UT (length 57000 km) and on 12 November at 16 57 UT (length 263 000 km) are discussed in this paper.     

Study of the post-flare loops on 29 July 1973

Bright and dark curvilinear structures observed between the two major chromospheric ribbons during the flare of 29 July 1973 on films from the Big Bear Solar Observatory are interpreted as a typical system of coronal loops joining the inner boundaries of the separating flare ribbons. These observations, made through a 0.25 Å H filter, only show small segments of the loops having Doppler shifts within approximately ± 22 km s^–1 relative to the filter passband centered at H, H -0.5 Å or H +0.5 Å. However, from our knowledge of the typical behavior of such loop systems observed at the limb in H and at 5303 Å, it has been possible to reconstruct an appoximate model of the probable development of the loops of the 29 July flare as they would have been viewed at the limb relative to the position of a prominence which began to erupt a few minutes before the start of the flare. It is seen that the loops ascended through the space previously occupied by the filament. On the assumption that H fine structures parallel the magnetic field, we can conclude that a dramatic reorientation of the direction of the magnetic field in the corona occurred early in the flare, subsequent to the start of the eruption of the filament and prior to the time that the H loops ascended through the space previously occupied by the filament.     

Filter observations of prominences in the D3 and Hα lines

D₃ and H pictures of prominences were obtained with a 21-in. Lyot coronograph and a Fabry-Perot etalon used as a narrow band filter. The monochromatic images of quiescent, quasiquiescent and loop-prominences were studied. The comparison of the isophotes of quiescent and quasi-quiescent prominences in D₃ with those in H shows the similarity of the prominence structure at both wavelength, although there is a strong tendency for an increase in the intensity ratio D₃/H in the upper region of prominences. It seems that it is due to lower temperature in the upper regions of prominences. Probably, the relaxation processes establishing ionization equilibrium play some role. Measurements of the knot intensities of the loop-prominence show strong variations of the intensity ratio D₃/H (more than one order of magnitude).     

Simultaneous radio and white light observations of the 1984 June 27 coronal mass ejection event

We present the two-dimensional imaging observations of radio bursts in the frequency range 25–50 MHz made with the Clark Lake multifrequency radioheliograph during a coronal mass ejection event (CME) observed on 1984, June 27 by the SMM Coronagraph/Polarimeter and Mauna Loa K-coronameter. The event was spatially and temporally associated with precursors in the form of meter-decameter type III bursts, soft X-ray emission and a H flare spray. The observed type IV emission in association with the CME (and the H spray) could be interpreted as gyrosynchrotron emission from a plasmoid containing a magnetic field of 2.5 G and nonthermal electrons with a number density of 10⁵ cm^–3 and energy 350 keV.On leave from Indian Institute of Astrophysics, Kodaikanal, India.     

Hα and hard X-ray development in two-ribbon flares

Morphological features of two-ribbon flares have been studied, using simultaneous ISEE-3 hard X-ray records and high-resolution Big Bear H movies for more than 20 events. Long-lasting and complex hard X-ray bursts are almost invariably found associated with flares of the two-ribbon type. We find at least three events, namely March 31, 1979, April 10, 1980, and July 1, 1980, where the occurrence of individual spikes in hard X-ray radiation coincides with suddenly enhanced H emission covering the sunspot penumbra. There definitely exist important ( 1B) two-ribbon H flares without significant hard X-ray emission.     

An analysis of photospheric vector magnetograms, Hα images and soft X-ray images in a superactive region NOAA 7321

Based on the photospheric vector magnetograms taken at Huairou Solar Observing Station (HSOS), H images taken at Hiraiso Solar Terrestrial Research Center of Communication Research Laboratory, soft X-ray images taken by Yohkoh and an extrapolation method, the magnetic field structures and some active phenomena of the active region AR 7321 around 04:12 UT on 27 October 1992 are analyzed in this paper. A divergence of the transverse magnetic field, located at a newly formed spot, was found. At least four highly sheared magnetic field systems separately spread from this divergence to four other sites around this divergence. Vertical current concentrations are upward in this region and downward in the other four sites, and the corresponding H bright patches and soft X-ray bright loops coincide with these structures, confirming the existence of these four systems. The extrapolated magnetic force lines reconstructed by the Boundary Element Method (BEM), force-free field assumption, and boundary condition of observed photospheric vector magnetic field, coincide in space with the H bright patches and soft X-ray bright loops, showing that this extrapolation method is very effective and suggesting that the H bright patches and soft X-ray bright loops in this case represent the magnetic field structures in the upper atmosphere of the Sun.The bright structures in the H images and the soft X-ray images have a close correlation with the non-potential characteristics of the magnetic fields.     

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.     

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.     

Precise determination of cooling times of post-flare loops from the detailed comparison between Hα and soft X-ray images

A detailed study of the evolution and cooling process of post-flare loops is presented for a large X9.2 solar flare of 2 November 1992 by using H images obtained with Domeless Solar Telescope at Hida Observatory and soft X-ray images of Yohkoh Soft X-ray Telescope (SXT). The detailed analysis with a new method allows us to determine more precise values of the cooling times from 10⁷ K to 10⁴ K plasma in the post-flare loops than in previous works. The subtraction of sequential images shows that soft X-ray dimming regions are well correlated to the H brightening loop structure. The cooling times between 10⁷ K and 10⁴ K are defined as the time difference between the start of soft X-ray intensity decrease and the end of H intensity increase at a selected point, where the causal relation between H brightening and soft X-ray dimming loops is confirmed. The obtained cooling times change with time; about 10 min at the initial stage and about 40 min at the later stage. The combined conductive and radiative cooling times are also calculated by using the temperature and density obtained from SXT data. Calculated cooling times are close to observed cooling times at the beginning of the flare and longer in the later stage.     

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 .     

Post-flare loops of 26 June 1992

Post-flare loops were observed on June 26, 1992 in the H line with the Multichannel Subtractive Double-Pass spectrograph (MSDP) on Pic-du-Midi and with the Swedish telescope on La Palma. The highly dynamic loops are inhomogeneous (blobs). The cool loops were observed 10–12 hours after the X 3.9 class flare which had a maximum on June 25 at 2011 UT. From 2D images obtained with the MSDP on June 26 we derive H intensities and Doppler velocities of the loop plasma. Using a geometrical reconstruction technique we show that these loops are mainly perpendicular to the solar surface and have the shape of a dipole magnetic configuration. We derive the bulk-flow velocities along the loop as a function of height using the Doppler velocities and the results from the loop reconstruction. Where the Doppler velocities are too small, we derive the bulk-flow velocities from the displacements of the falling blobs. We discuss existing deviations from free-fall velocity in the lower parts of the loops.     

VLA observations of interacting flaring loops

We present 4.9 GHz observations of an impulsive radio burst observed at the Very Large Array on 1981 May 16. The flare occurred in a complex active region containing several spots. The radio burst lay at the edge of an active-region microwave source, close to a neutral line. The compact burst showed morphological evidence for the presence of two loops in the rise phase, with the subsequent burst peak lying between these loops. This suggests that interaction between the loops played some role in the initiation of the flare. The flare spectrum is consistent with thermal gyrosynchrotron emission. The main microwave peak was displaced from the nearest H kernels by about 10, but there is strong evidence for post-flare loops coincident with the H kernels during the later stages of the event.     

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.     

Magnetic field configuration of active region NOAA 6555 at the time of a long-duration flare on 23 March 1991 – An Exception to Standard Flare Reconnection Model

The high-resolution H images observed during the decay phase of a long-duration flare on 23 March 1991 are used to study the three-dimensional magnetic field configuration of the active region NOAA 6555. Whereas all the large flares in NOAA 6555 occurred at the location of high magnetic shear and flux emergence, this long-duration flare was observed in the region of low magnetic shear at the photosphere. The H loops activity started soon after the maximum phase of the flare. There were a few long loop at the initial phase of the activity. Some of these were sheared in the chromosphere at an angle of about 45° to the east-west axis. Gradually, an increasing number of shorter loops, oriented along the east-west axis, started appearing. The chromospheric Dopplergrams show blue shifts at the end points of the loops. By using different magnetic field models, we have extrapolated the photospheric magnetograms to chromospheric heights. The magnetic field lines computed by using the potential field model correspond to most of the observed H loops. The height of the H loops were derived by comparing them with the computed field lines. From the temporal evolution of the H loop activity, we derive the negative rate of appearance of H features as a function of height. It is found that the field lines oriented along one of the neutral lines were sheared and low lying. The higher field lines were mostly potential. The paper also outlines a possible scenario for describing the post-flare stage of the observed long-duration flare.     

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.     

A comparison of the near-ultraviolet continuum and chromospheric emission line fluxes of the late-type giant stars

We investigate the near-ultraviolet high-resolution LWR spectra of the stars Cas, And, Tau, Gem, Cru, Boo, and Peg, obtained with the aid of the International Ultraviolet Explorer Satellite. We have given here a list of the strongest and most prevalent emission lines in the near-ultraviolet spectra of Boo, KlIIIp, and Peg, M2.5II-III which have the same luminosity class and different spectral type. The near-ultraviolet continuum flux measurements and integrated emission line fluxes of these stars for the 2500–3200 Å region are presented in order to compare the variations in the appearance of the near-ultraviolet flux distribution with the temperature structure of their chromospheres for K and M giant stars. We also discuss differences between observed and calculated fluxes found from the Planck function.     

The acceleration and propagation of solar cosmic rays as deduced from the relative abundance of protons to helium nuclei

Except for protons, the chemical composition of solar cosmic rays is very similar to the abundance of the elements at the photosphere of the Sun. If we consider the relative abundance ratio of protons to -particles (P/) at constant rigidity, this ratio is highly variable from one solar cosmic ray event to another. This ratio observed at the Earth, however, decreases monotonically with time from the onset of solar flares and, furthermore, is dependent on the heliocentric distance of the parent flares from the central meridian of the solar disk. P/'s which have been measured before the onset of SC geomagnetic storms change from 1.5 to 50 or more, being a function of the westward position of the source from the east limb of the Sun. These variations with respect to time and heliocentric distance suggest that the propagation of solar cosmic rays is strongly modulated in the interplanetary space. The major part of the -particles seem to propagate as if they are trapped within the magnetic clouds which produce SC geomagnetic and cosmic ray storms at the earth.The chemical composition and rigidity spectra of solar cosmic rays suggest that solar cosmic rays are mainly accelerated by the Fermi mechanism in solar flares. The observed variation of P/'s is produced mainly through the difference between the propagation characteristics of protons and -particles.NAS-NRC Associate with NASA.     

Flare and filament activation in an unusually distorted field configuration

Using photospheric and H observations and total radio flux data we study a two-ribbon flare in AR NOAA 4263 which was a part of a flare event complex on July 31, 1983. We find some facts which illuminate the special way of flare triggering in the analysed event. Around a double spot the photospheric vector magnetic field is discussed with respect to the chromospheric activities. In one of the spots the feet of long stretched loops are pushed down under steepening loops rooted in the same spot. This causes energy build-up by twist and shear in the stretched loops. One foot of the two-ribbon flare (triggered in the stretched and underpushed loop system) roots in a part of the spot umbra and penumbra where the field runs in extremely flat like a pressed spiral spring. A strange radio event, starting before the flares, can be interpreted as a precursor activity of the flare event complex. The radio data support the view that the analyzed flare process and the given magnetic field structure, respectively, are not very effective in energetic particle generation and escape.