Discovery of a complex spiral-shell structure around the oxygen-rich AGB star GX Monocerotis^⋆

¹ ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
e-mail: srandall@eso.org
² Academia Sinica Institute of Astronomy & Astrophysics (ASIAA), 11F of Astronomy-Mathematics Building, AS/NTU No.1, Section 4, Roosevelt Road, Taipei 10617, Taiwan
³ Joint ALMA Observatory, Alonso de Cordova 3107, Vitacura, Santiago 763 0355, Chile
⁴ Korea Astronomy and Space Science Institute 776, Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Republic of Korea
⁵ National Science Foundation, 2415 Eisenhower Ave., Alexandria, VA 22314, USA
⁶ Uppsala University, Department of Physics and Astronomy, Box 516, 75120 Uppsala, Sweden

Received: 26 April 2019
Accepted: 17 March 2020

Abstract

The circumstellar envelopes of asymptotic giant branch (AGB) stars exhibit a wide range of morphologies and chemical compositions that can be exploited to unravel their mass-loss history as well as binary status. Here, we present ALMA Band 6 observations centred upon the oxygen-rich, high mass-loss rate AGB star GX Mon. The resulting CO (2–1) map reveals an intricate, complex circumstellar spiral-arc structure consistent with hydrodynamical models for an AGB experiencing mass loss in a highly eccentric, close binary system with an orbital period of around 140 years. Several other transitions (including SiO, SiS, SO₂, and CS) are detected in the data, however only the SO (5–4) map shows a similar – although much weaker – distribution as imaged for the CO.