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[7.02] HST Fine Guidance Sensor Parallaxes for WZ Sge, YZ Cnc, and RU Peg: Calibration of the Outburst M_V - P_Orb Relationship for CVs

J. J. Johnson, T. E. Harrison (NMSU), S. B. Howell (UCR), P. Szkody (U. Wash.), B. E. McArthur, G. F. Benedict (UT-Austin)

We have used the Fine Guidance Sensors on the HST to generate high precision parallaxes for the cataclysmic variables WZ Sge, YZ Cnc, and RU Peg. These three objects span an orbital period range from 1.36 hr (WZ Sge) up to 8.99 hr (RU Peg). These new values, combined with existing HST parallaxes, allow us to calibrate the outburst absolute magnitude versus orbital period M_V - P_Orb relationship. We find a remarkably tight relationship after accounting for the orbital inclinations of the sample systems. In addition, we find that four other CV systems that exhibit rare outbursts of unknown type and for which we have HST FGS parallaxes (EX Hya, V1223 Sgr, TV Col, and RW Tri) are consistent with this relationship. This finding suggests that the rare outbursts of these four systems are due to normal dwarf nova disk instability events. We will also use optical and infrared photometry to examine the nature of the secondary stars in these systems.

Funding for this research has been provided by NASA through the HST Guest Observer program under grant GO-09089.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.