The separation of the stars in the binary nucleus of the planetary nebula Abell 35

Using the Planetary Camera on board the Hubble Space Telescope we have measured the projected separation of the binary components in the nucleus of the planetary nebula Abell 35 to be larger than 0.08′′ but less than 0.14′′. The system was imaged in three filters centered at 2950°A, 3350°A and 5785°A. The white dwarf primary star responsible for ionizing the nebula is half as bright as its companion in the 2950°A filter causing the source to be visibly elongated. The 3350°A setting, on the other hand, shows no elongation as a result of the more extreme flux ratio. The F300W data allows the determinination of the binary’s projected separation. At the minimum distance of 160 parsec to the system, our result corresponds to 18±5 AU. This outcome is consistent with the wind accretion induced rapid rotation hypothesis, but cannot be reconciled with the binary having emerged from a common-envelope phase.