THE PHOTOMETRIC PERIOD OF THE RECURRENT NOVA T-PYXIDIS

T Pyx is one of four known recurrent novae suspected to be powered by thermonuclear runaways. If the orbital period can be measured with high accuracy before the next eruption, then it may be possible to detect its period change caused by the eruption, which can then be directly related to the mass ejected from the system. This dynamical measurement of an important model parameter is independent of the various uncertainties that plague spectroscopic determinations of the mass loss. This paper presents 1713 photometric measurements from 1966 until 1990. The light curve of T Pyx shows roughly sinusoidal variations with a typical amplitude of 0.09 mag and time scale of 2 hr. Discrete Fourier transforms of data from individual nights and runs reveal a highly significant periodic modulation. We prove this modulation to be coherent only on time scales shorter than from 6 days to under 1 day. The variable period of T Pyx is disappointing since the modulation cannot be accurately tied to the orbital period, so that no pre-eruption orbital period will be available. We measure the modulation period with sufficient accuracy that the daily alias problem is probably solved. Our period for the modulations is 0.07616+/-0.00017 days. We note that other stars have variable photometric periods (possibly related to the superhump phenomenon) which are slightly different from the orbital period. so that we suggest an orbital period of near 0.073 days for T Pyx.