Kinematics of 1200 km/s Jets in He 3-1475

Abstract

Spectroscopic observations of a proto-planetary nebula He 3-1475 with the Space Telescope Imaging Spectrograph (STIS) reveal the kinematics of its high (1200 km/s) velocity jets. The jets are formed at a large (0.15 pc) distance from its central star by collimation of an asymmetric stellar wind in a pair of conical shocks seen in Wide Field Planetary Camera (WFPC2) images. The jets consist of several pairs of knots symmetrically distributed with respect to the central star, with most knots exhibiting a head-tail morphology. Large (up to 650 km/s) radial velocity gradients are seen within the knots on subarcsec scales, with velocities decreasing from the knot heads toward their trailing tails. These large velocity gradients are a sign of efficient deceleration of jets by a much slower bipolar outflow. The inclination angle of the bipolar outflow is equal to 40 degrees, based on Doppler shifts of the scattered stellar Halpha line. Its velocity is equal to 140 km/s at a distance of 0.23 pc from the star, and increases monotonically with the radial distance from the star. A comparison of new WFPC2 [N II] 6584 images with older WFPC2 images reveals expansion of the jets. The measured jet proper motions in combination with their radial velocities imply that He 3-1475 is a Galactic Bulge star at a distance of 8 kpc, located 800 pc above the Galactic plane. Its very high luminosity (25,000 solar luminosities) implies that He 3-1475 must be significantly more massive than a typical AGB star within the Galactic Bulge, perhaps because of a past mass transfer and/or a merger event in an interacting binary system.