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Session 79 - CVs and Novae.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center

[79.08] The Orbital Periods and Variability of the Nova-Like BK Lyncis (PG 0917+342) and the Dwarf Nova WW Ceti

F. A. Ringwald (PSI), J. R. Thorstensen (Dartmouth), R. K. Honeycutt, J. W. Robertson (Indiana), R. C. Smith (Sussex)

Long-term light curves of the cataclysmic variable BK Lyn (PG 0917+342) from the Indiana Automated CCD photometric telescope (``RoboScope'') and the Harvard College Observatory plate archive reveal no dwarf nova outbursts. Two radial velocity studies show its orbital period to be 107.97 \pm 0.07 minutes, confirming that it does have an orbital period shorter than the 2 -- 3-hour orbital period gap for cataclysmic variables. Whether this is a nova-like below the period gap or a dwarf nova with rare outbursts resembling WZ Sge is still unclear, but anomalously high angular momentum loss below the period gap may imply that magnetic stellar-wind braking still works below the period gap---but mass-losing secondary stars there are thought to be fully convective, and therefore should not have magnetic braking. If BK Lyn is a genuine nova-like beneath the period gap, it may provide evidence of magnetic activity occurring in the faintest M dwarfs, here in an interacting binary.

A radial velocity study resolves a long-standing aliasing problem and shows that the orbital period of the dwarf nova WW Cet is 0.17578 \pm 0.00013 d (4.22 hours). Its long-term light curves from RoboScope, AAVSO, Harvard archive, and VSS, RASNZ observations are examined. WW Cet does not have the characteristic standstills of the Z Cam stars, but does wander in quiescence by well over one magnitude. This and the orbital period become of interest in the context of recent speculation (Livio M., Pringle J. E., 1994, ApJ, 427, 956) that the low states of the VY Scl stars may be produced by star spots moving over L_1, choking off the mass flow, and that dwarf novae with orbital periods between 3 and 4 hours may be rare because of this.

Program listing for Wednesday