Morpho-kinematics of the wind of asymptotic giant branch star L2 Pup

Single-dish observations of asymptotic giant branch star L-2 Pup have revealed exceptionally low mass-loss rate and expansion velocity, challenging interpretations in terms of standard wind models. Recent VLT and ALMA observations have drawn a detailed picture of the circumstellar envelope within similar to 20 au from the centre of the star: a nearly edge-on rotating disc of gas and dust, probably hosting a planetary companion near the star. However, these observations provide no direct information on the wind escaping the gravity of the star. This article uses ALMA observations of the (CO)-C-12, 13(3-2), (SiO)-Si-29(8-7), (CO)-C-12(2-1), and (SiO)-Si-28(5-4) line emissions to shed new light on this issue. It shows the apparent normality of L-2 Pup in terms of the formation of the nascent wind, with important line broadening within 4 au from the centre of the star, but no evidence for a wind flowing along the disc axis. At larger distances, up to some 200 au from the centre of the star, the wind morpho-kinematics is dominated by a disc, or equatorial enhancement, expanding isotropically and radially with a velocity not exceeding some 5 km s(-1), inclined in the north-west/south-east direction with respect to the plane of the sky. In addition, outflows of lower density are observed on both sides of the disc, covering large solid angles about the disc axis, contributing about half the flux of the disc. Such morphology is at strong variance with the expectation of a pair of back-to-back outflows collimated by the central gas-and-dust disc.

Automated summary

This article presents ALMA observations of L-2 Pup, showing the formation and morphology of the wind and its movement at different distances and angles. The results challenge standard wind models and have important implications.