A long-standing enigma in planetary science has been the presence ofdaughter products of radioactive isotopes with short (τ ~ 106 yr) lifetimes. Some models are based on the injection of freshlysynthesized nuclides from stellar sources (e.g. a supernova remnant)into the molecular cloud from which the solar system formed. Othermodels produce these radionuclides within the disk via spallation byhigh fluences of MeV baryons. We report here the first quantitativemeasure of magnetic reconnection flaring in Myr-old analogs of theearly Sun from Chandra X-ray Observatory observations of the OrionNebula Cluster. We show that virtually all analogs of the ≤1Myr Sun exhibit X-ray flares that are ~30 times more powerful and~300 times more frequent than the most powerful flares seen onthe contemporary Sun. We infer that the proton fluence of the earlySun was 105 times that seen today, and argue that these protons mayplausibly have bombarded solids in the protoplanetary disk. Othershave demonstrated that such particle fluences are sufficient to produceseveral of the most troublesome excesses of short-lived CAI isotopesvia spallation of normal nebular material. Our results thus strengthenthe astronomical foundation for local irradiation models of meteoriticshort-lived isotopic anomalies. This work is described in detail byFeigelson et al.  (2002b).

The Sun's magnetic activity has changed considerably during its evolution from a protostar to a low-activity main-sequence star. The youngSun produced orders of magnitude more hot plasma, X-ray emission, and high-energyparticles. The present paper summarizes a few recent investigations onthe nature of the magnetic activity and associated high-energy processesin the Sun at different stages of its evolution,with emphasis on the physical mechanisms that may be responsible for coronal heating,the large-scale structure of the magnetic fields, and the possible mass-loss history ofthe Sun.

We summarize results of magnetic measurements of the bright early B-type stars β Cep, ζ Cas, and V2052 Oph, which we found to be oblique rotators with a weak magnetic dipole field with polar strength of a few hundred Gauss. From stellar wind studies we derived their rotational periods very accurately, and matched the magnetic and stellar wind phases. From model atmosphere fits we derived the angles of the rotation and magnetic axis. All three stars show some chemical abundance anomaly, likely associated with the magnetic properties. The stars are also pulsating variables. This is of high asteroseismological interest, since these are the only early-type stars known with observationally determined rotation, pulsation and magnetic properties.

We observed the ρ Ophiuchi dark cloud around core F, an active star-forming region, with the XMM-Newton observatory for 30 ks. We detected 107 X-ray sources within the 30' diameter field-of-view of the XMM-Newton observatory. We compared the positions of the XMM-Newton X-ray sources with the Chandra X-ray sources and found43 X-ray sources detected with both satellites.We had a high rate of X-ray detection of Class I protostars of ~70%.We extracted light curves and spectra from bright 4 Class I sources, YLW16A, EL29, YLW15, and IRS51.They did not show X-ray flare during the observation time of 30 ks.Their X-ray spectra showed high temperature and heavy absorption, which is typical for Class I protostars.

We analyse observations of the helium lines obtained with CDS onboard SOHO. The He i 584.3 Å/O iii intensity ratio shows a lower limit and an upper limit that decrease with increasing O iii intensity. At low O iii intensities this ratio increases significantly. An upper limit arises naturally if the enhancement mechanism involves turbulent motions transporting the helium atoms and ions through the steep transition region temperature gradient. The He i 537.0-Å/He i 584.3-Å and He ii 303.8-Å/He i 584.3-Å intensity ratios both decrease as the He i 584.3-Å line intensity increases. The values of the line ratios support the enhancement of the helium lines by turbulent motions, but appear to rule out the enhancement due to excitation by non-thermal coronal electrons.

The 3D analysis (x, y, t) of the granulation intensity field (11-hour time sequence from Swedish Vacuum Solar Telescope onLa Palma, Canary Islands), demonstrated that the granules in the phostosphere are organized in ``Trees of Fragmenting Granules" (TFGs). A TFG consists of a family of repeatedly splitting granules, issued from one granule at its beginning. A striking result is that TFGs can live much longer (up to 8h10) than individual granules (10 mn). When averaged in time, such long-lived TFGs can be identified to the mesogranules. We also found a correlation between the network and the spatial distribution of TFGs.