Magnetohydrodynamics of Mira’s cometary tail

Abstract

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 farultraviolet emission. We suggest an emission process that involves C 0 excitation through inelastic electron collisions and a two-photon continuum to explain the luminosity of Mira's tail.

The Fate of AGB Wind in Massive Galaxies and the ICM

“…Wareing (2012) further assumes that Mira entered the Local Bubble at an angle to explain the observed kink of the tail. Since Mira itself is not the focus of this work, we instead use a simpler setup assuming Mira has always been in the Local Bubble, similar to Gómez (2013), which allows us to focus on the effects of mixing and cooling. Even without fine-tuning Mira's environment or trajectory, our simulated tail of Mira already bears remarkable resemblance to the observed tail.…”

Planetary nebulae with UVIT

“…Gómez (2013) causally suggests neutral C excitation through inelastic collisions of 3 P-1 D transitions might provide FUV emission -but we are not sure that this would work here (might contribute to a minor extent? ).…”