A slowly expanding disk and fast bipolar outflow from the S star π1 Gruis

We study the molecular outflow of the nearby evolved S star pi(1) 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 similar to 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 degrees 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 similar 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.