The Necklace Nebula as a probe of close binary evolution
Abstract
Mass loss from evolved stars is a fundamental but poorly understood process. In particular, the production of collimated outflows is observed in a large variery of sources, and evolution in interacting binaries has been traditionally invoked to explain it. The Necklace Nebula was only discovered in 2011 but is proving to be a key target to investigate this issue: it is one of the few planetary nebulae for which the association between close-binary evolution and the formation of jets was established, and the only one for which the jet ejection process can be directly associated with accretion on the secondary star. In particular, accretion would have occurred right before the onset of a fast evolutionary phase in which the two stars share a common envelope {CE} and then eject it. Pre-CE accretion is supported by the gas kinematical ages, and most important by our finding that the secondary star is carbon-rich, a fact that can naturally be explained by accretion from the wind of the primary when the latter was a carbon-rich AGB star. The decisive test to confirm this hypothesis, tying all loose ends about the evolution of the system, is to prove that the nebular gas is also carbon-rich. For this reason, we aim to determine the C/O abundance ratio of the nebula using COS. The HST is needed because the dominant C and O ions can only be detected at FUV wavelengths. Confirmation of our hypothesis will provide for the first time a fully consistent description of the mass loss, mass transfer and mass accretion processes occurring during CE, a phase that is crucial to understand classes of objects such as cataclysmic variables, novae, low-mass X-ray binaries, and SNIa.
- Publication:
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HST Proposal
- Pub Date:
- October 2013
- Bibcode:
- 2013hst..prop13424C