Energy release in solar flares

Team 2 of the Ottawa FLARES 22 Workshop dealt with observational and theoretical aspects of the characteristics and processes of energy release in flares. Main results summarized in this article stress the global character of the flaring phenomenon in active regions, the importance of discontinuities in magnetic connectivity, the role of field-aligned currents in free energy storage, and the fragmentation of energy release in time and space.Report of Team 2, Flares 22 Workshop, Ottawa, May 25–28, 1993.     

A cross-correlation analysis of tidal current,water temperature and salinity records

Fifteen day records of current velocity, water temperature and salinity were obtained at a coastal station in the Seto Inland Sea. It was observed that water movement was characterized by an exchange of two distinctive water masses east and west of the station. Cross-correlation analysis shows that, at the semi-diurnal period, the motion of these characteristic waters causes temperature and salinity variations. At frequencies higher than 2 cycles per day where power spectra of current velocity have a slope of ?5/3, coherence between current velocity and both water temperature and salinity decreases rapidly.     

The circumstellar gas of sigma orionis E

In order to explain the variable H emission and the eclipse-like light variation of Ori E, we investigated the circumstellar gas trapped by the stellar magnetic field and corotating with the star. By considering the potential along the magnetic field line, we found that the gas concentrates to a potential minimum. The circumstellar gas forms either two condensations or a disk, depending on the inclination of the magnetic dipole to the stellar rotation axis. The geometrical thickness of the circumstellar disk, of about 0.2 stellar radii, and the distance from the center of the star to the inner edge of the disk, of about 3 stellar radii, were obtained. The H emission line profile at its maximum phase and the amplitude of light variation were calculated by assuming the isothermal gas in LTE with the maximum gas density which the magnetic field can hold. The model gives good agreement with observation in the low obliquity case, and also explains the phase correlation among the H emission maximum, the light minimum, and the magnetic extreme. The model, however, failed to explain the large IR excess in theM band.     

The luminosity function for the globular cluster M15

We obtained the luminosity function from the Main-Sequence turnoff region to the subgiants for M15 (V=17.0–19.6), using plates taken by the Kitt Peak 4 m reflector. The measured region isr=2.5–8.0 zone. We extrapolated the star counts to the cluster center and to the tidal limit, using King's (1966) photometry, Kinget al.'s (1968) counts, Peterson and King's (1975) result, and Simoda and Iben's (1970) theoretical results.The comparison of the observed function with the theoretical ones by Simoda and Iben (1970) indicates that the observation is consistent with the theory forX0.9±0.1, thus marginally inconsistent with the Big Bang cosmology value (X=0.76). The comparison with Bertelliet al. (1970) theoretical ones gives contradictory results. Possible causes of this problem are the improper extrapolation of star counts to the cluster center and/or the inaccuracies of the theoretical luminosity functions so far published, and/or the impropriety of the canonical structure and evolution theory of Population II stars. In the last two cases, the ages and the helium abundances of globular clusters may vary.We also obtained the luminosity function for blue horizontal branch stars fromV=17.0 to 19.6.Kitt Peak National Observatory, U.S.A., which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

The Hard X-ray Telescope (HXT) for the SOLAR-A mission

The Hard X-ray Telescope (HXT) is a Fourier-synthesis imager; a set of spatially-modulated photon count data are taken from 64 independent subcollimators and are Fourier-transformed into an image by using procedures such as the maximum entropy method (MEM) or CLEAN. The HXT takes images of solar flares simultaneously in four energy bands, nominally 15 (or 19)–24, 24–35, 35–57, and 57–100 keV, with an ultimate angular resolution as fine as 5 arc sec and a time resolution 0.5 s. Each subcollimator has a field of view wider than the solar disk. The total effective area of the collimator/detector system reaches 70 cm², about one order of magnitude larger than that of the HINOTORI hard X-ray imager. Thanks to these improvements, HXT will for the first time enable us to take images of flares at photon energies above 30 keV. These higher-energy images will be compared with lower-energy ones, giving clues to the understanding of nonthermal processes in solar flares, i.e., the acceleration and confinement of energetic electrons. It is of particular importance to specify the acceleration site with regard to the magnetic field figuration in a flaring region, which will be achieved by collaborative observations between HXT and the Soft X-ray Telescope on board the same mission.After the launch the name of SOLAR-A has been changed to YOHKOH.     

Japanese Astrometry Satellite Mission for Infrared Exploration

JASMINE is the name of a Japanese infrared (K-band) scanning astrometric satellite. JASMINE (I and/or II-project) is planned to be launched between 2013 and 2017 and will measure parallaxes and proper motions with the precision of 10μas at K≃ 12 - 15 mag. JASMINE will observe a few hundred million stars belonging to the disk and the bulge components of our Galaxy, which are hidden by the interstellar dust extinction in optical bands. Furthermore, JASMINE will also obtain photometry of stars in K, J and H-bands. The main objective of JASMINE is to study the most fundamental structure and evolution of the disk and the bulge components of the Milky Way Galaxy. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the origin of subsecond pulses at 17 GHz

We have analyzed three flare events with subsecond structures in hard X-rays (CGRO/ BATSE) and 17 GHz data (Nobeyama radioheliograph). It was shown that microwave subsecond brightenings (SSB) were generated by directly precipitating electrons with energy of 100–200 keV from tiny regions close to footpoints. In two events, when high correlation between microwaves and X-rays was observed, the SSB can be interpreted in terms of gyrosynchrotron emission. Plasma emission seems to be a more credible explanation of the spontaneous pulses in the event when poor correlation with X-rays was observed.     

Examining the aerosol indirect effect over China using an SO2 emission inventory

The relationship between SO₂ emissions and the effective particle radius of low-level water clouds (r_e) over China was investigated to determine anthropogenic effects on clouds. Sulfur dioxide emission values were obtained from a statistical inventory, and r_e origins were retrieved by satellite remote sensing on a 0.5° grid. Comparisons between annual mean SO₂ emissions and r_e showed generally decreasing r_e values, explained by the Twomey effect. The existence of the Twomey effect is supported by comparisons with simulated aerosol optical depths. Results further suggest that clouds over land show sensitivity to the Twomey effect as well as clouds over the ocean.