Eyes in the sky: Interactions between AGB winds and the interstellar magnetic field

Abstract

We aim to examine the role of the interstellar magnetic field in shaping the extended morphologies of slow dusty winds of Asymptotic Giant-branch (AGB) stars in an effort to pin-point the origin of so-called eye shaped CSE of three carbon-rich AGB stars. In addition, we seek to understand if this pre-planetary nebula (PN) shaping can be responsible for asymmetries observed in PNe. Hydrodynamical simulations are used to study the effect of typical interstellar magnetic fields on the free-expanding spherical stellar winds as they sweep up the local interstellar medium (ISM). The simulations show that typical Galactic interstellar magnetic fields of 5 to 10 muG, are sufficient to alter the spherical expanding shells of AGB stars to appear as the characteristic eye shape revealed by far-infrared observations. The typical sizes of the simulated eyes are in accordance with the observed physical sizes. However, the eye shapes are of transient nature. Depending on the stellar and interstellar conditions they develop after 20,000 to 200,000yrs and last for about 50,000 to 500,000 yrs, assuming that the star is at rest relative to the local interstellar medium. Once formed the eye shape will develop lateral outflows parallel to the magnetic field. The "explosion" of a PN in the center of the eye-shaped dust shell gives rise to an asymmetrical nebula with prominent inward pointing Rayleigh-Taylor instabilities. Interstellar magnetic fields can clearly affect the shaping of wind-ISM interaction shells. The occurrence of the eyes is most strongly influenced by stellar space motion and ISM density. Observability of this transient phase is favoured for lines-of-sight perpendicular to the interstellar magnetic field direction. The simulations indicate that shaping of the pre-PN envelope can strongly affect the shape and size of PNe.

Accepted for publication in A&A. Final version will contain animated results

References in corpus (8)

• Evolution of interstellar dust and stardust in the solar neighbourhood
• The interaction of planetary nebulae and their AGB progenitors with the interstellar medium
• The spatial energy spectrum of magnetic fields in our Galaxy
• The enigmatic nature of the circumstellar envelope and bow shock surrounding Betelgeuse as revealed by Herschel. I. Evidence of clumps, multiple arcs, and a linear bar-like structure
• Computing the dust distribution in the bowshock of a fast moving, evolved star
• Large-scale environments of binary AGB stars probed by Herschel - I. Morphology statistics and case studies of R Aquarii and W Aquilae
• Enhanced Cosmic Ray Flux and Ionization for Star Formation in Molecular Clouds Interacting with Supernova Remnants
• Probing the Magnetized Interstellar Medium Surrounding the Planetary Nebula Sh 2-216

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• Models of the Mass-Ejection Histories of pre Planetary Nebulae, III. The Shaping of Lobes by post-AGB Winds
• Infrared dust arcs around the stars: I. effect of the radiation pressure
• A detailed view on the circumstellar environment of the M-type AGB star EP Aquarii I. High-resolution ALMA and SPHERE observations
• Mapping circumstellar magnetic fields of late-type evolved stars with the Goldreich-Kylafis effect: CARMA observations at $\lambda 1.3$ mm of R Crt and R Leo
• Modelling O-star astrospheres with different relative speeds between the ISM and the star: 2D and 3D MHD model comparison
• History of the mass ejection in K 4-37: from the AGB to the evolved planetary nebula phase
• The dusty envelopes of asymptotic giant branch stars with ultraviolet excesses