Common envelope evolution in born-again planetary nebulae -- Shaping the H-deficient ejecta of A30

TL;DR

This paper presents the first detailed morpho-kinematic model of the H-deficient ejecta in the born-again planetary nebula A30, revealing a disrupted disk and bipolar ejections, and proposes a common envelope phase as the shaping mechanism.

Contribution

It introduces the first morpho-kinematic model of A30's H-deficient material, linking its structure to a common envelope phase after a very late thermal pulse.

Findings

Disrupted disk tilted 37° with respect to the line of sight.

Faster expansion of the inner disrupted disk compared to bipolar features.

Proposed common envelope phase explains the structure and abundance discrepancies.

Abstract

Born-again planetary nebulae (PNe) are extremely rare cases in the evolution of solar-like stars. It is commonly accepted that their central stars (CSPN) experienced a very late thermal pulse (VLTP), ejecting H-deficient material inside the evolved H-rich PN. Given the short duration of this event and the fast subsequent evolution of the CSPN, details of the mass ejection are unknown. We present the first morpho-kinematic model of the H-deficient material surrounding a born-again PN, namely A30. New San Pedro M\'{a}rtir observations with the Manchester Echelle Spectrograph were recently obtained to map the inner region of A30 which are interpreted by means of the software SHAPE in conjunction with HST WFC3 images. The SHAPE morpho-kinematic model that best reproduces the observations is composed by a disrupted disk tilted $37^\circ$ with respect to the line of sight and a pair of orthogonal opposite bipolar ejections. We confirm previous suggestions that the structures closer to the CSPN present the highest expansion velocities, that is, the disrupted disk expands faster than the farther bipolar features. We propose that the current physical structure and abundance discrepancy of the H-deficient clumps around the CSPN of A30 can be explained by a common envelope phase following the VLTP event. Our proposed scenario is also compared with other known born-again PNe (A58, A78, HuBi1 and the Sakurai's Object).