Alastair G. Gunn

Multiwavelength Observations of Flares on AD Leonis

We report results from a multiwavelength observing campaign conducted during 2000 March on the flare star AD Leo. Simultaneous data were obtained from several ground- and space-based observatories, including observations of eight sizable flares. We discuss the correlation of line and continuum emission in the optical and ultraviolet wavelength regimes, as well as the flare energy budget, and we find that the emission properties are remarkably similar even for flares of very different evolutionary morphology. This suggests a common heating mechanism and atmospheric structure that are independent of the detailed evolution of individual flares. We also discuss the Neupert effect, chromospheric line broadening, and velocity fields observed in several transition region emission lines. The latter show significant downflows during and shortly after the flare impulsive phase. Our observations are broadly consistent with the solar model of chromospheric evaporation and condensation following impulsive heating by a flux of nonthermal electrons. These data place strong constraints on the next generation of radiative hydrodynamic models of stellar flares.

A spectroscopic study of the eclipsing binaries SV Camelopardalis and XY Ursae Majoris

High-resolution spectroscopic observations of the eclipsing RS CVn-type active close binaries SV Camelopardalis and XY Ursae Majoris reveal excess emission components in the H α and H β lines. We have used the spectral subtraction technique to separate the excess emission from the photospheric background and find that in both stars the excess emission is associated with the secondary, cooler component. Analysis of the

The VSOP 5 GHz AGN survey I. Compilation and observations

EW_{\rm{H\alpha}}

Radio and extreme-ultraviolet observations of CF Tucanae

/

ECLIPSING BEHAVIOUR OF THE RADIO EMISSION IN THE ALGOL SYSTEM V505 SAGITTARII

EW_{\rm{H\beta}}

An optical flare on YZ Canis Minoris

ratio indicates that in both cases the emission is probably associated with surface plage regions or prominences viewed against the stellar disks. We find no evidence of excess absorption features associated with extended prominence-like material in these systems.