The planetary nebula abandoned by its central star
Citations Over TimeTop 13% of 1994 papers
Abstract
Narrowband images have been obtained of the nebula Sh 2-174, to follow up the recent claim that the white dwarf situated on one edge, GD 561, is its displaced central star. The H alpha and (N II) emission originates from the cleft-hoof morphology apparent on the POSS, but the (O III) is centred on the white dwarf. This confirms that the star and the nebula are physically related. With the severely distorted morphology apparent in H alpha and (N II) combined with the location of the former central star, Sh 2-174 represents the most advanced case so far of the Planetary Nebula-Interstella Medium (PN-ISM) interaction. Spectra taken of GD 561 suggest a surface gravity log g approximately equals 6.8 and effective temperature Teff approximately equals 65 000 K. Assuming a standard single star evolution, this would lead to an exceptionally low mass and a post-AGB age of approx. ten million years, which is incompatible with the several hundred thousand years which is generally supposed to be a typical PN lifetime. We suggest instead that GD 561 is part of a close binary system, having lost its outer envelope after the termination of core H burning, and is now a small approx. 0.3 solar mass degenerate He dwarf. However, this scenario requires the existence of a faint companion.
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