ABSTRACT. We study the molecular outflow of the nearby evolved S star π¹ Gru. We imaged the outflow in CO J = 2-1 and dust continuum with the Submillimeter Array. The CO emission was detected over a very broad velocity width of ~90 km s^-1. Our high-resolution images show that the outflow at low velocities (≤15 km s^-1) is elongated east-west and at high velocities (≥25 km s^-1) is displaced north (at redshifted velocities) and south (blueshifted velocities) of center as defined by the dust continuum source. We model the spatial-kinematic structure of the low-velocity outflow as a flared disk with a central cavity of radius 200 AU and an expansion velocity of 11 km s^-1, inclined by 55° to our line of sight. We attribute the high-velocity component to a bipolar outflow that emerges perpendicular to this disk with a velocity of up to ~45 km s^-1. This high-velocity outflow may play an important role in shaping the gas envelope previously ejected by the AGB star and thus produce a bipolar morphology when the object evolves into a proto-planetary nebula.

Subject headings: circumstellar matter; stars: AGB and post-AGB; stars: individual (π Gruis)

Print publication: Issue 1 (2006 July 1)
Received 2005 October 18, accepted for publication 2006 March 15