THE PULSE-TIMING AND EMISSION-LINE ORBITS OF THE WHITE-DWARF IN THE CATACLYSMIC VARIABLE AE-AQUARII

The nova-like variable AE Aqr is a binary star with an orbital period of 9.88 hr, consisting of a K5 V star and a white dwarf. The white dwarf is magnetized, and it is accreting mass transferred from the K5 V star onto its two magnetic poles. The white dwarf rotates with a period of 33.08 s causing flashes of unequal strength every 16.5 s. The orbital motion of the white dwarf has been estimated from the radial velocity curve of the emission lines produced in the accreting gas around the white dwarf and from the times of arrival of the 33.08 s pulses. We have remeasured both the emission-line and the pulse-timing orbits of AE Aqr. From the emission-line orbit we derive an improved value for the orbital period, 0.4116580(+/- 2) days, and an improved value for the amplitude of the radial velocity variations, K(em) = 141 +/- 8 km s-1. Based on our new photometry, the revised ephemeris for the 16.5 s component of the 33 s modulation is T(max) = BJED 2,445,171.999844(+/- 1) + 0.000191416425(+/- 1)E, and the semiamplitude of the pulse-timing orbit is 2.30 +/- 0.07 s, which is equivalent to K(pulse) = 122 +/- 4 km s-1. We show that the pulse-timing orbit is distorted, probably by reprocessing of the pulses in the accreting gas, and cannot be used to estimate the orbit of the white dwarf reliably. The emission-line orbit appears to be unusually free of complications and is a better estimator of the orbit of the white dwarf. Adopting the spectroscopic orbital elements for AE Aqr, we find M(K) sin3 i = 0.54 +/- 0.05 M., M(wd) sin3 i = 0.62 +/- 0.05 M., and q = M(wd)/M(K) = 1.13 +/- 0.06. The orbital inclination lies between 63-degrees and 70-degrees.