Morphology and kinematics of the gas envelope of Mira Ceti

• Published in: Monthly notices of the Royal Astronomical Society Vol. 460; no. 1; pp. 673 - 688
• Main Authors: Nhung, P. T., Hoai, D. T., Diep, P. N., Phuong, N. T., Thao, N. T., Tuan-Anh, P., Darriulat, P.
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 21.07.2016
• Subjects: Asymmetry; Doppler; Doppler effect; Envelopes; Hemispheres; Kinematics; Morphology; Outflow; Star & galaxy formation; Stars; Velocity; stars: AGB and post-AGB; stars: individual: Mira AB; radio lines: stars; circumstellar matter
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw996

Observations of 12CO(3–2) emission of the circumbinary envelope of Mira Ceti, made by Atacama Large Millimetre/sub-millimetre Array, are analysed. The observed Doppler velocity distribution is made of three components: a blueshifted south-eastern arc, which can be described as a ring in slow radial expansion, ∼1.7 km s−1, making an angle of ∼50° with the plane of the sky and born some 2000 years ago; a few arcs, probably born at the same epoch as the blueshifted arc, all sharing Doppler velocities redshifted by approximately 3±2 km s−1 with respect to the main star; thirdly, a 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 arcsec, 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−1 and is slightly redshifted; the north-eastern outflow consists of two arms, both blueshifted, bracketing a broad dark region where emission is suppressed. At distances between ∼1.5 and ∼2.5 arcsec 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−1, which we interpret as gas flowing from Mira A towards Mira B.