ALMA observations of the nearby AGB star L2 Puppis II. Gas disk properties derived from 12CO and 13CO J = 3–2 emission

Abstract

The circumstellar environment of the AGB star L-2 Puppis was observed with ALMA in cycle 3, with a resolution of 15 x 18 mas. The molecular emission shows a differentially rotating disk, inclined to a nearly edge-on position. In the first paper in this series ( Paper I) the molecular emission was analysed to accurately deduce the motion of the gas in the equatorial regions of the disk. In this work we model the optically thick (CO)-C-12 J = 3-2 and the optically thin (CO)-C-13 J = 3-2 rotational transition to constrain the physical conditions in the disk. To realise this effort we make use of the 3D NLTE radiative transfer code LIME. The temperature structure and velocity structure show a high degree of complexity, both radially and vertically. The radial H-2 density profile in the disk plane is characterised by a power law with a slope of -3:1. We find a (CO)-C-12 over (CO)-C-13 abundance ratio of 10 inside the disk. Finally, estimations of the angular momentum in the disk surpass the expected available angular momentum of the star, strongly supporting the indirect detection of a compact binary companion reported in Paper I. We estimate the mass of the companion to be around 1 Jupiter mass.