A study of the eclipsing cataclysmic variable Lanning 90

Abstract

Photometric and spectroscopic observations of Lanning 90 (V1776 Cyg) show that it is an eclipsing cataclysmic variable with an orbital period of 3h57m. The shape of the eclipse is variable, and the brightness out of eclipse can change by over a magnitude in less than a day. The broad-band light curves do not show a hump before eclipse, but time-resolved spectroscopy of one orbit suggests that the H-alpha emission-line strength peaks near phase 0.75. Observations of a number of orbits, however, are needed to confirm that the line strength depends on phase. The velocity amplitude of the primary is 144 + or - 20 km/s as measured from the wings of the H-alpha line. The masses of the components, the orbital inclination, and semimajor axis are estimated from the observations, but the derived system parameters are suspect since the spectroscopic phase lags the photometric phase by 70 deg. A similar shift has been observed in DW UMa and is attributed to a disturbance on the disk which contaminates the Balmer line wings. 20 refs.