PI: Howard E. Bond, Space Telescope Science Institute, email@example.com
Address: 3700 San Martin Drive, Baltimore, MD 21218, USA
CoI: Orsola De Marco, American Museum of Natural History
CoI: Dianne Harmer, NOAO
Title: Searching for Spectroscopic Binaries Among Central Stars of Planetary Nebulae
Abstract: \everypar=\looseness=-1 In 2002-4, we used the WIYN Hydra spectrograph to search for radial-velocity (RV) variations among planetary-nebula nuclei (PNNi). Our aim was to find spectroscopic binaries with periods of several days to weeks. This program was very successful: 10 out of 11 PNNi were found to have variable RVs. Combined with the fact that ~10% of PNNi were already known to be very short-period binaries (as shown by photometric variations), it seemed possible that most or even all planetary nebulae (PNe) are ejected from binary systems. However, we were not able to determine definitive orbital periods for any of our WIYN RV variables, because the RV amplitudes are low, and the WIYN scheduling was optimized to find long periods, whereas it appears that the periods of our candidates are actually fairly short. It thus remains conceivable that we are actually observing some other phenomenon, such as variability in stellar-wind profiles, that mimics RV variations. We now propose to continue an alternative approach begun in May 2005, in which we intensively monitor our candidates for 5 consecutive nights, using the high spectral resolution of the KPNO 4m telescope's echelle spectrograph. The aim is to yield high-accuracy RVs and orbital periods, or possibly reveal changes in line profiles characteristic of wind variability. In spite of instrumental and weather problems in May 2005, we found very promising results, which we will build on in 2006. Our program bears on the questions of the origin of compact binaries, the shaping of PNe, and whether single stars produce visible PNe at all.
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