Morphology and kinematics of the gas envelope of Mira Ceti

TL;DR

This study uses ALMA observations of CO emission to analyze the complex morphology and kinematics of Mira Ceti's gas envelope, revealing multiple arcs, outflows, and gas flows between binary components.

Contribution

It provides a detailed kinematic and morphological analysis of Mira Ceti's circumbinary envelope, highlighting new arc structures and gas flow dynamics.

Findings

Identified a slow-expanding ring-like arc ~2000 years old.

Detected asymmetric outflows with distinct morphologies near the star.

Observed gas flow from Mira A to Mira B within the envelope.

Abstract

Observations of 12CO(3-2) emission of the circumbinary envelope of Mira Ceti, made by ALMA are analysed. The observed Doppler velocity distribution is made of three components: a blue-shifted south-eastern arc, which can be described as a ring in slow radial expansion, ~1.7 km/s, making an angle of ~50 deg with the plane of the sky and born some 2000 years ago; a few arcs, probably born at the same epoch as the blue-shifted arc, all sharing Doppler velocities red-shifted by approximately 3 +/- 2 km/s with respect to the main star; the third, central region dominated by the circumbinary envelope, displaying two outflows in the south-western and north-eastern hemispheres. At short distances from the star, up to ~1.5", these hemispheres display very different morphologies: the south-western outflow covers a broad solid angle, expands radially at a rate between 5 and 10 km/s and is slightly red shifted; the north-eastern outflow consists of two arms, both blue-shifted, bracketing a broad dark region where emission is suppressed. At distances between ~1.5" and ~2.5" the asymmetry between the two hemispheres is significantly smaller and detached arcs, particularly spectacular in the north-eastern hemisphere are present. Close to the stars, we observe a mass of gas surrounding Mira B, with a size of a few tens of AU, and having Doppler velocities with respect to Mira B reaching +/-1.5 km/s, which we interpret as gas flowing from Mira A toward Mira B.