| Issue |
A&A
Volume 558, October 2013
|
|
|---|---|---|
| Article Number | A107 | |
| Number of page(s) | 7 | |
| Section | Interstellar and circumstellar matter | |
| DOI | https://doi.org/10.1051/0004-6361/201322080 | |
| Published online | 14 October 2013 | |
Magnetohydrodynamics of Mira’s cometary tail
Department of Chemistry and Physics, Western Carolina University, Cullowhee, North Carolina 28723, USA
e-mail: egomez@email.wcu.edu
Received: 14 June 2013
Accepted: 26 July 2013
Aims. The asymptotic giant-branch, long-period variable star Mira exhibits a 4 parsec long cometary tail in the far-ultraviolet. We address the issue of the origin of this structure and its emission process by simulating the transition of this star from the interstellar medium to the Local Bubble, which is a tenuous, high-pressure medium.
Methods. We use the hydrodynamic and the magnetohydrodynamic modules of the PLUTO astrophysical code to carry out our simulations. We study the system without a cooling function, with a simplified exponential cooling function, and with a simplified nonequilibrium cooling function.
Results. We find evidence that magnetohydrodynamics constrain the shape of the cometary tail and explain features of its far-ultraviolet emission. We suggest an emission process that involves C0 excitation through inelastic electron collisions and a two-photon continuum to explain the luminosity of Mira’s tail.
Key words: radiation mechanisms: thermal / stars: AGB and post-AGB / ISM: magnetic fields / methods: numerical / shock waves / ISM: jets and outflows
© ESO, 2013
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