Abstract
It is widely believed that the dramatic transformation of the spherical outflows of AGB stars into the extreme aspherical geometries seen during the planetary nebula (PN) phase is linked to binarity and driven by the associated production of fast jets and central disks/torii. The key to understanding the engines that produce these jets and the jet-shaping mechanisms lies in the study of objects in transition between the AGB and PN phases. I discuss the results of our recent studies with high-angular-resolution (with ALMA and HST) and at high-energies (with GALEX, XMM-Newton and Chandra) of several such objects, which reveal new details of close binary interactions and high-speed outflows. These include two PPNe (the Boomerang Nebula and IRAS 16342-3814), and the late carbon star, V Hya. The Boomerang Nebula is notable for a massive, high-speed outflow that has cooled below the microwave background temperature, making it the coldest object in the Universe. IRAS 16342-3814 is the prime example of the class of water-fountain pre-planetary nebulae or PPNe (very young PPNe with high-velocity H2O masers) and shows the signature of a precessing jet. V Hya ejects high-speed bullets every 8.5 years associated with the periastron passage of a companion in an eccentric orbit. I discuss our work on AGB stars with strongly-variable high-energy (FUV, X-ray) emission, suggesting that these objects are in the early stages of binary interactions that result in the formation of accretion disks and jets.
Highlights
The fundamental question that has motivated the Planetary Nebulae conference series is: How do the slowly expanding (5–15 km s−1 ), largely spherical, circumstellar envelopes (CSEs) of AGB stars transform themselves into highly aspherical Planetary Nebulae (PNe), with collimated lobes and fast −1 outflows (>∼ f ew × 100 km s ) along one or more axes? The importance of collimated jets in forming ansae in PNe was recognized in [1]
Emission, suggesting that these objects are in the early stages of binary interactions that result in the formation of accretion disks and jets
Based on the wide variety of multipolar and point-symmetric morphologies seen in unbiased surveys of young PNe with HST, reference [2] proposed that collimated fast winds or jets, operating during the pre-planetary nebula (PPN) or very late-AGB
Summary
The fundamental question that has motivated the Planetary Nebulae conference series is: How do the slowly expanding (5–15 km s−1 ), largely spherical, circumstellar envelopes (CSEs) of AGB stars transform themselves into highly aspherical Planetary Nebulae (PNe), with collimated lobes and fast. I describe our observational techniques for searching for binarity (and signatures of associated active accretion) in AGB stars, as well as observational results from our recent studies of three key transition objects that have likely undergone recent (or are currently undergoing) close binary interactions. These objects show large and sudden mass-ejections prior to the formation of a planetary nebula, as well as disks, torii and (episodic) high-speed, collimated jets. The paper is based on an invited talk that I gave at the Asymmetrical Planetary Nebulae (APN) VII meeting (Hong Kong, December 2017)
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