High-Speed Optical Spectroscopy of a Cataclysmic Variable Wind: BZ Camelopardalis

BZ Camelopardalis is the first cataclysmic variable star with an accretion disk wind evident in its optical spectrum. The wind was found by Thorstensen, who discovered intermittent P Cygni profiles occurring simultaneously in He i lambda5876 and Hα. We have since obtained spectra with 0.4 Å pixel^-1 dispersion and 60 s time resolution. We find a much faster and more rapidly variable wind than the radiatively accelerated ones of OB stars, Wolf-Rayet stars, or luminous blue variables. Instead of showing blob ejection, the whole wind of BZ Cam appears to turn on and off. We use this to measure the acceleration law of a CV wind for the first time. The velocity increases linearly with time, attaining blue edge velocities near -3000 km s^-1, and absorption velocities near -1700 km s^-1, in 6 to 8 minutes after starting near rest. We also find a subsequent linear deceleration to nearly rest in 30-40 minutes, perhaps an effect of dilution as the wind expands. No periodicity from rotational outflow is obvious. This wind is erratic and incessantly variable, and perhaps bipolar and face-on, but not highly collimated. The P Cygni absorption events trace out sawtooth waves, occurring within 30 to 40 white dwarf radii from the disk. This is the approximate size of the disk, as well as the disk/wind transition region recently postulated by Knigge & Drew. We estimate a distance of 830 +/- 160 pc and an orbital inclination i such that 12 deg <~ i < 40 deg.