The Long Aftermath of Superoutbursts: STIS Results on AL Comae 5.5 Years Past Outburst

Abstract

The Space Telescope Imaging Spectrograph (STIS) was used to obtain the ultraviolet spectrum of AL Comae 5.5 yr past its 1995 April superoutburst. The spectrum can be fitted by a model of a logg=8+/-0.5 white dwarf with a temperature of 16,300+/-1000 K. Surprisingly, the flux distribution is exactly the same as the Faint Object Spectrograph data obtained 4.5 yr earlier, but the UV fluxes are a factor of 2 lower than the previous measurement, while the optical fluxes remained the same. The implication could be that the temperature of the UV component has remained very similar, but the size of the emitting area has decreased by ~30%. Alternatively, there could be multiple components contributing in the UV, with corresponding changes in temperature and size that produce a similar flux distribution at the two epochs.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Scence Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555, and with the Apache Point Observatory (APO) 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium.