The Rapidly Evolving Asymptotic Giant Branch Star, v Hya: ALMA Finds a Multiring Circus with High-velocity Outflows

We have observed the mass-losing carbon star V Hya that is apparently transitioning from an asymptotic giant branch star to a bipolar planetary nebula, at an unprecedented angular resolution of ∼1/40.″4-0.″6 with the Atacama Large Millimeter/submillimeter Array. Our 13CO and 12CO (J = 3-2 and J = 2-1) images have led to the discovery of a remarkable set of six expanding rings within a flared, warped disk structure undergoing dynamical expansion (DUDE) that lies in the system's equatorial plane. We also find, for the first time, several bipolar, high-velocity outflows, some of which have parabolic morphologies, implying wide-opening angles, while one (found previously) is clumpy and highly collimated. The latter is likely associated with the high-velocity bullet-like ejections of ionized gas from V Hya; a possible molecular counterpart to the oldest of the four bullets can be seen in the 12CO images. We find a bright, unresolved central source of continuum emission (FWHM size ∼310-5 M ∼. We have used a radiative transfer model to fit the salient characteristics of the DUDE's 13CO and 12CO emission out to a radius of 8″ (3200 au) with a flared disk of mass 1.7 × 10-3 M ∼, whose expansion velocity increases very rapidly with the radius inside a central region of size ∼1/4200 au, and then more slowly outside it, from 9.5 to 11.5 km s-1. The DUDE's underlying density decreases radially, interspersed with local increases that represent the observationally well-characterized innermost three rings. © 2022. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu