Simultaneous Multiwavelength Observations of Dwarf Novae Systems at Quiescence and in Outburst

Abstract

The results of photometric and spectroscopic observations of dwarf novae are presented. The data were obtained during an international program of multiwavelength observations, held in 1986 February at several observatories, of dwarf novae during the first and subsequent days of outburst. During the campaign numerous dwarf novae were monitored in order to catch them in outburst. Preliminary results and analysis of some objects are reported elsewhere. A total of 30 dwarf novae were observed in the northern and southern hemispheres. Among them 37% were caught in outburst, including 10% on the rise to outburst and 17% in decline. Photometric observations were carried out in the UBVRI system and colour indexes were calculated. Colour-colour diagrams and light curves of the particular stars were constructed. U - B, B - V and V - R, B - V diagrams are presented in Figs. 1 and 2 respectively. The data shown in Figs. 1 and 2 confirm many results obtained previously, and shows clustering of the objects, depending on their orbital periods, above the main sequence at minimum (Echevarria 1984; Echevarria, Costero & Michel 1993). This region is a very large one, reflecting differences in types of dwarf novae. SU UMa type stars and other short period systems are considerably bluer in both U - B and B - V colours. During an outburst cycle, the systems trace a loop on the colour-colour diagram, with the general pattern shown in the U - B, B - V diagram.