The Radio-X-ray Relation in Cool Stars: Are we headed toward a divorce?

This splinter session was devoted to reviewing our current k nowledge of correlated X-ray and radio emission from cool stars in order to prepare for new large radio observatories such as the EVLA. A key interest was to discuss why the X-ray and radio luminosities of some cool stars are in clear breach of a correlation that holds for other active stars, the so-called Gudel-Benz relation . This article summarizes the contributions whereas the actual presentations can be acce ssed on the splinter website 1 . 1. Radio emission and X-rays as diagnostics of coronal energy release X-rays and radio emission are excellent diagnostic probes t o study energy release in magnetized stellar coronae. Solar observations have been key to deciphering the plethora of phenomena seen in these wavelength ranges. In brief, X-rays trace the presence of dense, hot (million-degree) plasma trapped in closed coronal magnetic fields, heated by processes that are still not fully understood. Radio obse rvations, in contrast, probe both thermal atmospheric components from the chromosphere to the corona, and popu- lations of non-thermal, accelerated electrons, typically residing in low-density, open or closed coronal magnetic fields. A solar-stellar analogy is, however, complicated by phenomenology in magnet- ically active stars that is, at first sight, not present in the Sun. X-ray emission be- comes much stronger toward more active stars, most likely as a result of increased sur- face coverage with active regions; however, the average, "characteristic" temperature of the corona increases along with the coronal luminosity (e.g., Schrijver et al. 1984; Gudel et al. 1997), a trend that requires additional physic al explanation. At radio wave- lengths, magnetically active stars also show a different face. Solar radio emission in the