Космическое черенковское излучение

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A Statistical Analysis of Faint Hα Coronal Emission Associated with Prominences

The results from a detailed study of the prominences associated with faint H emission objects in the solar corona are given. The frequency distribution of the prominences by their lifetime, as well as for the prominence groups with and without `disparition brusque' (DB), is presented. The systematic comparison of the time of the prominence DBs and the observation time of the objects with faint H emission, as well as the positions of the faint H emissions and the associated filaments at the limb and on the disk of the Sun, suggests that in the most cases these coronal emissions are probably closely connected with the instability processes operating in the prominence magnetic field configurations and leading to prominence final or temporary DBs.     

A search for discrete gamma-ray sources of energy greater than 2×1012 eV

The results of the observations to search gamma-ray sources with the energy greater than 2×10¹² eV, which were made in Crimean Astrophysical Observatory during the years 1969–73 are presented. A technique of the detection of the EAS Cerenkov flashes was used.The quality of the data obtained is analysed. The criteria for the selection of the data free from meteorological variations are considered.It was shown that two objects, namely, Cyg X-3 and Cas -1, may be the sources of high-energy gamma quanta. It is probable that the object with the coordinates =05^h15^m, =+1° is the source of gamma-rays as well. An unidentified object Cas -1 is variable: gamma-ray flux was observed twice — in Sepember–October 1971 and in December 1972. It is possible that the flux from Cyg X-3 has a period of 4.8 hr.

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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.     

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.     

Some calculations bearing on the heating and cooling of quiescent prominences

We discuss the evolution of pulses of heat both along and perpendicular to magnetic fields threading quiescent prominences. We show that while heating of prominence material can take place on a time scale of the order 10³ s (of the same order as the observed winking of H light from prominences and also of the same order as the dynamical Alfvén time scale across a prominence sheet) individual flux tubes are effectively thermally insulated from neighboring tubes, since the transverse (to the ambient supporting magnetic field) heat conduction time scale is of order 10⁴ yr. The exact solution to the one-dimensional parallel heat conduction problem is shown to differ significantly from the approximate solution reported by Ioshpa (1965). We also suggest that uneven heating of a quiescent prominence by the surrounding solar corona may be a contributory mechanism for surges and/or the observed winking phenomenon - both of which are recorded in many quiescent prominences. The signature of such a temperature pulse would be a sharp (10³ s) brightening of continuum radiation with a correlated decrease in the free-bound emission, followed by a slow (10⁴ s) recovery of both to their pre-heat pulse levels.     

Structure and stability of prominences with helical structure

Observations of internal structure and development of four helical prominences are presented. We assume that the helically twisted fine structure threads are outlining magnetic field lines and we found that it is possible to describe the magnetic fields by the uniform twist configuration, with the twists ranging between 2 and 7. The estimated lower limits for the magnetic fields were about 20 G which give lower limits for the currents flowing along the prominences in the range between 2 × 10¹⁰ A and 2 × 10¹¹ A and current densities at the axis of the prominences about 10^-4 A m^-2. The upper limit of electron drift velocity could be estimated as 1 m s^-1, which is far below the critical velocities for the onset of plasma microinstabilities.The stability of the studied prominences is discussed and the criteria for the onset of eruptive instability are established for a prominence modelled as a twisted and elliptically curved magnetic flux tube which is anchored in the photosphere and affected by its mirror-current. The eruption starts when the prominence attains a critical height which must be larger than half of the footpoint separation and depends on the values of twist, radius, and footpoint distance of the magnetic flux tube. The observed examples of eruptive prominences agree very well with the predictions. Possible applications to the two-ribbon flare process are outlined.Properties of stable cylindrical prominences in equilibrium are analyzed and a criterion for the distinction between the Kuperus-Raadu and Kippenhahn-Schlüter types of prominences is proposed. According to established criteria, two of the studied prominences were of the Kuperus-Raadu type, while the other two were of the Kippenhahn-Schlüter type.     

Классикаци дбиижэхий в обобщэхной плоцкой задачэ трех неподБижнΨη цэнтпов

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On the classification of motion in the generalized two-dimensional problem of three fixed centres

A qualitative analysis and classification of forms of motion in the problem under consideration have been carried out using a method (applicable to any case of integrability) due to Liouville. All the forms of the two-dimensional motions for any masses (negative and complex as well) at fixed centres corresponding to the real potential have been considered.

     

Околозвездньiе облака поданньiм ультрафиолетовьiх спектров свезл

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Evolution of helically twisted prominence structures of March 11, 1979

Helical structures are generally associated with many eruptive solar prominences. Thus, study of their evolution in the solar atmosphere assumes importance. We present a study of a flare-associated erupting prominence of March 11, 1979, with conspicuous helically twisted structure, observed in H line center. We have attempted to understand the role played by twisted force-free magnetic fields in this event. In the analysis, we have assumed that the helical structures visible in H outline the field lines in which prominence tubes are embedded. Untwisting of observed prominence tubes and later, formation of open prominence structures provide evidence of restructuring of the magnetic field configuration over the active region during the course of prominence eruption. Temporal evolution of the force-free parameter is obtained for two main prominence tubes observed to be intertwined in a rope-like structure. Axial electric currents associated with the prominence tubes are estimated to be of the order of 10¹¹ A which decreased with time. Correspondingly, it is estimated that the rate of energy release was 10²⁸ erg s^–1 during the prominence eruption.     

Physical conditions in eruptive prominences at several solar radii

SMM data from the Corograph/Polarimeter experiment giving intensities of H and continuum emission in eight erupting prominences are analyzed to obtain the physical conditions in the regions of H emission. Since the H intensity depends upon three unknowns whereas only two independent observations are available, it is necessary to assume one additional condition in order to obtain unique solutions. Solutions are chosen that give the maximum expansion of the prominence volume as reflected by minimum values of the electron density. These solutions correspond closely with those giving the best agreement between the gas pressure in the prominence and the ambient coronal pressure. Electron densities are found to be of the order of 10⁸ cm^-3 at temperatures near 2 × 10⁴ K.The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research under sponsorship of the National Science Foundation.     

Analysis of extreme-ultraviolet spectroheliograms of solar prominences

The optical depth at the head of the Lyman continuum, _H, is determined at a number of positions in three hedgerow prominences using spectroheliograms (5 × 5 resolution) of C III 977, LC 896, and O IV 554 observed with the Harvard experiment on Skylab. At heights greater than 10 above the limb the maximum value of _H is 30 to 50, which occurs at the central part of the prominences. For one of the prominences the determination of _H is found to be consistent with data from spectroheliograms of Mg X 625. The degree of ionization of hydrogen is estimated from the intensity of LC 896 at _H 1. In the central part of a model prominence N _P/N _HI1.9 for a reasonable range of the electron densities, where N _P and N _HI are the proton density and the neutral hydrogen density, respectively.     

Observations of helium and hydrogen emission in quiescent prominences

Observations of a number of helium triplet ( 10830, 4713, 4471, 3889, 4026) and hydrogen (H, , , ) emission line intensities in six quiescent prominences are presented. The regions of prominence and neighboring corona were raster-scanned by the telescope, and all lines were measured concurrently at each point. The instrumental field of view was 5 × 20. The results are compared with previous observations and theory. In particular, the intensity of the 10830 emission relative to the other triplets is found to differ strongly from the predictions of the recent detailed calculations of Heasley et al. (1974) for model quiescent prominences.     

Splintering loop prominences

A new type of sunspot prominences (splintering loop prominences) is described. They have loop structure, but their material seems to originate from the lower layers. A tentative interpretation of the new type is given. In the splintering loop prominences on October 7, 1967 a phenomenon was observed which might be interpreted as the capture of an ejected prominence streamer by transverse magnetic fields of the loops.On leave from the Astronomical Institute of the Czechoslovak Academy of Sciences, Ondejov.     

The orientation of magnetic fields in quiescent prominences

We have measured the longitudinal component, B, of the magnetic field in quiescent prominences and obtained a relationship between B and , where is the angle between the long axis of the prominence and the north-south direction on the sun. From this relationship we deduce a distribution function for the magnetic field vector in quiescent prominences in terms of the angle between the field and the long axis of the prominence. The mean angle, , for our data is small, - 15°, indicating that the magnetic field traverses quiescent prominences under a small, but finite angle.On leave from Max-Planck Institut für Physik und Astrophysik, München.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Magnetic Dips in Prominences

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

Comparison of Prominences in Hα and He II 304 Å

In this letter, we bring attention to prominences which show different morphology in H and Heii 304 Å, as observed simultaneously by BBSO and EIT on board SOHO. Those two lines have been thought to represent similar chromospheric structures although they are formed at significantly different temperatures. We give two examples representing two kinds of anomaly: (1) prominences showing strong H emissions in the lower part and strong Heii emissions in the upper part, and (2) erupting prominences showing extensive Heii emission, but nothing in H. Our results indicate that a part or the whole of a prominence may be too hot to emit H radiation, possibly due to heating or thermal instability. Please note that these are not just two isolated cases, many other prominences show the similar differences in H and Heii 304 Å.     

An apparent ‘even-odd’ cycle distribution in Mt. Wilson ‘numbers of spots’ data

Mt. Wilson numbers of spots data (as defined in Howard et al., 1984) appear to be distributed according to even-odd cycle numbering. Linear fits of annual numbers of spots versus annual sunspot number for even- and odd-numbered cycles have slopes which are statistically different at the 5% level of significance. The existence of an even-odd split in Mt. Wilson numbers of spots data may be due either to a real difference in even- and odd-numbered cycles on the Sun or to a difference in weather at Mt. Wilson (perhaps, related to the 22-yr rhythm of drought in the western United States) during even- and odd-numbered cycles, or both. For cycle 22, an even-numbered cycle, the peak numbers of spots is estimated to be near 2600.     

Rapid changes in the fine structure of a coronal ‘bright point’ and a small coronal ‘active region’

A coronal bright point is resolved into a pattern of emission which, at any given time, consists of 2 or 3 miniature loops (each 2500 km in diameter and 12 000 km long). During the half-day lifetime of the bright point individual loops evolved on a time scale 6 min. A small ctive region seemed to evolve in this way, but the occasional blurring together of several loops made it difficult to follow individual changes.