Hrivnak, B. ; Bohlender, D. ; Kerber, F. ; Lu, W. ; Seifahrt, A. ; Van de Steene, G. ; Van Winckel, H.

published in Asymmetrical Planetary Nebulae VI Conference, pp. 39 (2014)

Abstract: Binaries are often invoked as a shaping mechanism for the asymmetrical shapes of planetary nebulae and proto-planetary nebulae (PPNe) - particularly those that are elliptical, bipolar, or point symmetric. To test this hypothesis, we have been carrying out radial velocity monitoring of a sample of PPNe. The results of an initial study of seven bright PPNe have been published, based primarily on our observations from 1991-1995 and 2007-2010 at the Dominion Astrophysical Observatory (Victoria, Canada). Six of the seven showed no long-term variations between the two time intervals while one, IRAS 22272+5435, gave evidence of a variation consistent with a P > 22 yr (Hrivnak et al. 2011, ApJ, 734, 25). All seven of these objects do show shorter-term pulsational variations, on the order of 35-130 day over a range of about 14 km/s (peak-to-peak). We have expanded this search in two ways. Firstly, we have increased the temporal baseline by continuing to monitor the bright seven objects in radial velocity and increased the sampling with the addition of observations from the Hermes spectrograph on the Mercator telescope (Canary Islands). This has resulted in a second object with possible long-term variability that may indicate a binary companion. Secondly, we have started to monitor three edge-on PPNe with near-infrared spectroscopy; the stars are hidden in visible light but seen in the near infrared. These should show the full orbital velocity if it exists. Observations were begun in 2010, primarily from the ESO-VLT. While the spectra are more complicated than expected, we have found tantalizing evidence for systematic velocity variations in one of these three. Preliminary results for both of these expanded studies were presented. The research is supported in part by a grant from the NSF to BJH (AST-1009974).

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