Spiral-shells and nascent bipolar outflow in CIT 6: Hints for an eccentric-orbit binary?

Hyosun Kim

ASIAA, Taiwan

Protoplanetary nebulae (pPNe) often consist of outer rings (or arcs) and inner bipolar (or multipolar) structures. The coexistence of such geometrically distinct structures is commonly interpreted as due to the shape transition from spherically-symmetric envelopes of asymptotic giant branch (AGB) stars to highly-asymmetric PNe. The bipolar outflows are hypothesized as the outcome of "close" binary interaction, while the typical dynamical timescales of the observed ring patterns are consistent with the orbital periods of "wide" binaries. This puzzle may be resolved with highly eccentric orbit binaries whose close periastrons allow the binary interactions and consequent accretion processes onto a companion star. The carbon star, CIT 6, at the tip of the AGB reveals evidences for the eccentric binary orbit in a high-resolution CO emission map from our Submillimeter Array observations. In this poster, we present the wonderful complexity of CIT 6, consisting of the spiral-shell pattern, bipolar (possibly multipolar) outflow, one-sided interarm gaps, and double spiral feature. All these features point to a plausible scenario with an eccentric orbit binary.

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