Extreme Ultraviolet and Optical Observations of The AM Herculis Type Cataclysmic Variable V884 Herculis (RX J1802.1+1804)

Abstract

ABSTRACTWe observed V884 Herculis (RX J1802.1+1804), during a high accretion state, from 1997 September 17–22 UT using the Extreme Ultraviolet Explorer (EUVE) satellite. Simultaneously, multiple ground‐based optical telescopes obtained photometric observations. Although the EUV flux was too low for spectral study, the light curve from the Deep Survey instrument provides useful information on the system geometry. The phased, folded EUV light curve shows a brief total eclipse similar to previous ROSAT PSPC data followed by a broad dip. The optical light curve shows a lower amplitude of variability and a smoother structure. The similarity of the optical light curves on all six nights, along with previous magnetic measurements, and the coincidence of the periods determined from the optical and EUVE data, confirm the synchronism of this system and its classification as an AM Her type magnetic cataclysmic variable. Doppler tomography of 1995 high state spectra reveals a short, ballistic accretion stream with little emission from an irradiated secondary star. An optical light curve obtained in 1998 June shows the system during a lowered accretion state, with a mean magnitude that is ∼1.5 mag fainter than the high state. The low state light curve displays a smaller amplitude of orbital variation but only slight changes in accretion geometry. A spectrum obtained 15 days later shows that the optical continuum had returned to a high state, although the line strengths appear different from past high states.