A second post-AGB nebula that contains gas in rotation and in expansion: ALMA maps of IW Carinae

摘要

Aims. We aim to study the presence of both rotation and expansion in post-AGB nebulae, in particular around IW Car, a binary post-AGB star that was suspected to be surrounded by a Keplerian disk. Methods. We obtained high-quality ALMA observations of 12CO and 13CO J = 3?2 lines in IW Car. The maps were analyzed by means of a simplified model of CO emission, based on those used for similar objects. Results. Our observations clearly show the presence of gas components in rotation, in an equatorial disk, and expansion, which shows an hourglass-like structure with a symmetry axis perpendicular to the rotation plane and is probably formed of material extracted from the disk. Our modeling can reproduce the observations and shows moderate uncertainties. The rotation velocity corresponds to a central stellar mass of approximately 1 M⊙. We also derive the total mass of the molecule-rich nebula, found to be of ~4 × 10-3M⊙; the outflow is approximately eight times less massive than the disk. From the kinematical age of the outflow and the mass values derived for both components, we infer a (future) lifetime of the disk of approximately 5000–10?000 yr.