Mathematics – Logic
Scientific paper
Dec 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aas...189.9704b&link_type=abstract
American Astronomical Society, 189th AAS Meeting, #97.04; Bulletin of the American Astronomical Society, Vol. 28, p.1401
Mathematics
Logic
6
Scientific paper
We report photometric observations of the central stars of three planetary nebulae (PNe) which appear to be thin circular rings. All three central stars have proven to be close binaries, from CCD observations made at the CTIO and KPNO 0.9-m telescopes. The southern-hemisphere PN Sp 1 is a nearly perfect circular ring. Its central star has a light curve which is a low-amplitude sinusoid with a period of 2.9 days, suggesting a reflection effect in a binary system seen nearly pole-on. We therefore suggested (Bond & Livio, ApJ 355, 568, 1990) that the nebula must be a true toroidal annulus, likewise seen nearly pole-on. SuWt 2 is another southern PN, which appears as a thin ellipse. If it were an Sp 1-like PN, seen almost edge-on, and also ejected from a close binary, we might hope to detect actual stellar eclipses. This has proven to be the case: the central star is an eclipsing binary with a period of 4.8 days. WeBo 1 is a northern PN recently discovered by Webbink and Bond. Morphologically the nebula is extremely similar to SuWt 2, in being an almost mathematically perfect ellipse. Recent observations at KPNO reveal that its central star is also a close binary, with a sinusoidal light curve and a period of approximately 5 days. It is thus becoming clear that some close binaries can undergo a common-envelope interaction that results in a much shorter orbital period accompanied by ejection of a thin nebular ring. Parallels with other objects, including SN 1987A, should be explored.
Bond Howard E.
Ciardullo Robin
Webbink Ron
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