Theoretical astrophysics and plasma physics at RPC

Abstract:

As part of our study of the formation of the lines of He I and He II, observations of these lines and of other transition region and coronal lines have been made with the CDS on SOHO using hi-rate telemetry These give repeated 25-s exposures of the quiet Sun allowing time-dependent studies which complement our previous studies of the spatial variation of the He I, He II and other transition region lines. Network brightenings are observed which are similar to those previously reported by others. The variations of He I and He II lines with time have a smaller amplitude than those of the other transition region lines. This could be due in part to the higher opacity of the helium lines. Lines shifts and linewidths have also been investigated; some of our results confirm those found earlier, but many of the large downflows in the supergranulation cell boundaries are adjacent to, rather than co-spatial with, the highest intensities. An order of magnitude brightening, followed by a strong upflow and large turbulent velocities is also observed, and may be a small 'network flare'.