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

Abstract

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 arcsec but less than 0.14 arcsec. The system has been imaged in three filters centred at 2950, 3350 and 5785 Angstroms. The white dwarf primary star responsible for ionizing the nebula is half as bright as its companion in the 2950-Angstroms filter, causing the source to be visibly elongated. The 3350-Angstroms setting, on the other hand, shows no elongation as a result of the more extreme flux ratio. The F300W data allow the determinination of the projected separation of the binary. At the minimum distance of 160 pc 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.