ULTRACAM photometry of the ultra-compact binary V407 Vul

Abstract

V407 Vul is a 20<SUP>th</SUP> magnitude star that varies on a period of 570 seconds at both X-ray and optical wavelengths. Its properties lead Cropper et al (1998) to suggest that this is the orbital period of two white dwarfs. We present photometry of V407 Vul taken simultaneously in u', g' and i'. We find that the pulsations are progressively delayed when one moves to shorter wavelengths. We find no modulation in the position of V407 Vul on the sky, indicating that the G/K star in its spectrum is less than 0.03 arcseconds on the sky away from the variable.