An analysis of the emission line spectra of AG Pegasi between phases 7.34 and 9.44

Marcella Contini

Published 2002-10-10Version 1

The UV and optical spectra from the HST FOS and from the FAST spectrograph at the Whipple Observatory at different phases are analysed, leading to new results about the configuration of AG Peg. Consistent modelling by the code SUMA, which accounts for the coupled effect of photoionisation from the hot star and the shock, shows the important role of at least three nebulae: 1) the nebula between the stars, downstream of the shock created by collision of the winds, which propagates in reverse towards the WD, 2) the nebula downstream of the shock expanding in the outskirts of the giant atmosphere, and 3) the shock propagating outwards the binary system, that is not reached by the hot source radiation. The relative contribution of the three nebulae to the final spectra at different phases are calculated for all the lines. It is found that the contribution to the different lines changes with the viewing angle of the system. The relatively low preshock density and magnetic field adopted in the modelling of the expanding shocks reveal that they are merging with the ISM, thus explaining the slow decline of AG Peg.