Arnold Benz

New observational signatures of the heating process(es) have been revealed by space missions including SoHO, TRACE, Yohkoh, and RHESSI. Evidences for heating in the quiet corona, active region loops, and the solar wind are different and must be distinguished. Prime indications come from line broadening and waves, the distribution of temperature and radiation loss in relation to height, the correlation of magnetic flux and brightness, nanoflares and other fluctuations. This review concentrates on microevents observed at coronal temperatures. The reported nanoflares in quiet regions are about 2 orders of magnitude smaller than microflares reported in active regions and exhibit less radio emission. To estimate the impact of these microevents on the corona, the effects from a localized energy release must be considered, regardless of the energy source (reconnection or waves). In particular, the coupling with the chromosphere, i.e. the back-reaction of the chromosphere on coronal energy ...

ABSTRACT Do elementary time scales exist in solar flares that could provide us a clue on the spatial fragmentation of the primary energy release process? Or is there a continuous distribution, composed of a hierarchy of unresolved time structures? We present results of two recent studies on these fundamental questions. We applied a multi-resolution analysis (using triangle-shaped wavelet transforms) to 647 solar flares observed with the COMPTON Gamma Ray Observatory (CGRO) at hard X-ray energies of >= 25 keV with a time resolution of 64 ms. From the wavelet scalegrams we infer a distribution of time scales N(T) for each flare and find a cutoff for the shortest detected time scales Tmin that is independent of the Poisson noise for strong flares. These shortest time scales Tmin are found to correlate with the flare loop radius r (Fig.1), i.e. Tmin = 0.5 (r/10^9 cm)s (measured with Yohkoh) and the collisional deflection time, Tmin > ~tDefl(n_e), (determined from the electron density n_e of trapped electrons by measuring energy-dependent time delays detected with CGRO). From these observations we infer spatial sizes of racc = 75-750 km for elementary acceleration cells. In a second study we determined the frequency distributions of elementary time structures in over 600 flares, based on some 10^4 hard X-ray pulses at 25 and 50 keV, 4000 radio type III bursts, 4000 decimetric quasi-periodic broadband pulsation events, and 10^4 decimetric millisecond spike events. All elementary time structures have a quasi-Gaussian shape and can be modeled with the logistic equation, which describes the exponential growth phase and nonlinear saturation (caused by the limited amount of available free energy) of a general instability. We derive a theoretical description of frequency distributions in terms of this logistic avalanche model and find that the power-law slope of observed frequency distributions provides a powerful diagnostic on coherent versus incoherent instabilities.

Division II consists of Commissions 10 (Solar Activity), 12 (Solar Radiation and Structure), and 49 (Interplanetary Plasma and Heliosphere). More detailed information on IAU activities in each of these three areas can be found in the individual reports of the respective Commissions.The Division II OC briefly considered changes to the structure of our Division in response to opportunities offered by the Executive Committee during this triennium. However, we believe that the present structure works well and change is not warranted at this time.

We conclude that the ground state transitions of H2O trace the outer parts of the envelopes, so that the effects of star formation are mostly noticeable in the outflow wings. These lines are heavily affected by absorption, so that line ratios of H2O involving the ground states must be treated with caution. The average H2O abundance in high-mass protostellar envelopes does not change much with time. The 987 GHz line appears to be a good tracer of the mean weighted dust temperature of the source, which may explain why it is readily seen in distant galaxies.

We report observations of the T Tauri system at 8.4 GHz with a VLBI array comprising the VLBA VLA and Effelsberg 100m telescopes. We detected a compact source offset approximately 40mas from the best optical position of the T Tau Sb component. The other system components (T Tau Sa T Tau N) were not detected in the VLBI data. The

The emission of decimetric flare radiation, in particular narrowband spikes and pulsations, is generally considered to originate from accelerated, non-thermal particles. On the other hand, non-thermal hard X-rays (HXR) are well accepted results of such acceleration. Are radio emissions and HXR signatures of the same acceleration process? Good correlation of the light curves in the radio and HXR range may evidence it. The correlation of decimetric radio emission and HXR in solar flares was analysed using data from the RHESSI spacecraft and the Phoenix-2 spectrometer in Bleien (Switzerland). For the first time we have the possibility of a systematic search on the radio-HXR relation in the range from 100 MHz to 4 GHz. The measured delays have a distribution with a FWHM of 4.9 s and 4.7 s for pulsations and spikes, respectively, evaluated from a Gauss fitting method. The mean delay for pulsations was found to be -1.4± 0.9 seconds (minus indicates that hard X-rays emission comes first), and for narrowband spikes to -2.5±2.5 seconds. The delays do not depend on centre frequency, cross-correlation coefficient, duration of the correlating sequence and position on the disc. However, we find an increase in delay for the spikes with GOES magnitude (peak soft X-ray emission) of the flare and with peak hard X-ray flux.

... the pressure of the source magnetic field B = 2irvmc/es ~ 6.4 G (using the minimum energy hypothesis The detection of the dwarf nova EM Cyg with ... In the case ofa (Benz et al., 1983) and one of Turner's (1985) sources (TY Psc) source twice as large as the binary dimension the ...