Background
Single star evolutionary channels are still thought to be at the root of the
evolution of most Planetary Nebulae (PNe).
Despite the fact that most PNe are not circular, binary channels have been thought to be of secondary importance,
mostly due to the fact that only a handful of binarie central stars of PN have ever been found. Recent
theoretical work has however convinced a sizable amount of PN astronomers that binarity might play a much more
important role in the formation and shaping of PNe than previously acknowledged.
I lead a working group, aptly names PlaN-B,
for Planetary Nebula Binaries, which aims at determining new detection techniques to test observationally the PN binary hypothesis.
My role
Radial Velocity surveys of central stars of PN. With Howard Bond (STScI), Di Harmer (NOAO) as well as two
students we are collecting radial velocity (RV)
data of a sample of central stars of PN with the aim of determining if they are binaries.
Our initial work showed that 10 of the 11 stars for which a sufficient amount of data has
been obtained are RV variables down to the limit of our technique. This suggested that
a large fraction of central stars might be in binaries.
As the worked continued to look for periods, it became clear that the nature of the
variability cannot readily be attributed
to binarity, though no other cause can trivially explain it either. We are therefore continuing
observations to characterize the variability and detemrine whether it can be linked to a companion.
We also started a new search in collaboration with Ralf Napiwotzki (University of Hertfordshire), Albert Zijlstra (Jodrell Bank),
and Thomas Rauch (University of Tuebingen)
using UVES at the VLT, using the experience and technique of the SPY poject
(Search for Type Ia SN double degenerate progenitors).
With Todd Hillwig (Valparaiso University) and several students, we have also started a new photometric variability (similar to the search originally carried out by Bond and collaborators). This survey should be able to detect binaries with periods smaller than a week.
In collaboration with Howard Bond (STScI), George Jacoby (WIYN Telescope), and Patrick Harrington (University of Meryland), we have a new HST program to image PNe in globular clusters. We suspect that these objests have derived from stellar mergers or common envelope interactions where the binary has survived.
Publicatons
Binary central stars of PN discovered through photometric variability. I. What we know and what we would like to find out
De Marco, O., Hillwig, T., Smith, A.J., 2008, AJ in press
The Bizarre Spectral Variability of Central Stars of Planetary Nebulae
De Marco, O., Wortel, S., Bond, H.E., Harmer, D., 2008, Asymmetric PN IV, in press
Indications of a Large Fraction of Spectroscopic Binaries among Nuclei of Planetary Nebulae
De Marco, O., Bond, H.E., Harmer, D., & Fleming, A.F., 2004, ApJ Letters 602, 93
Do Most Planetary Nebulae Derive from Binaries? I. Population Synthesis Model of the Galactic Planetary Nebula Population Produced by Single Stars and Binaries
Moe, M., & De Marco, O., 2006, ApJ 650, 916
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