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H. E. Bond (STScI), K. Exter, D. L. Pollacco (Queen's U. Belfast)
The southern planetary nebula (PN) SuWt~2 appears as an elliptical ring, with much fainter bipolar lobes. The ring is presumed to be a circular structure, seen nearly edge-on. Thus the PN shows an extreme degree of density contrast between material ejected into the orbital plane and perpendicularly to it.
The central star has been found to be an eclipsing binary with a period of 4.9~days, confirming that we do view the star/nebula system nearly edge-on, and suggesting that the PN was ejected as the consequence of a common-envelope binary interaction. Remarkably, the binary consists of two A-type stars of nearly equal brightness. We discuss whether a ``born-again'' scenario can account for one of the A~stars, which was recently the source of ionizing radiation but has now become cooler. However, our spectroscopic radial-velocity observations of the double-lined binary show that both stars have masses of order 2\,M\odot, making the born-again interpretation unlikely. We will discuss other possible explanations for this extraordinary system.
The author(s) of this abstract have provided an email address for comments about the abstract: bond@stsci.edu