Kinematics of 1200 Kilometer per Second Jets in He 3‐1475

Abstract

Spectroscopic observations of a proto-planetary nebula He 3-1475 with the Space Telescope Imaging Spectrograph reveal the kinematics of its high-velocity (1200 km s-1) 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 2 (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-1) radial velocity gradients are seen within the knots on subarcsecond 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°, based on Doppler shifts of the scattered stellar Hα line. Its velocity is equal to 140 km s-1 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] λ6584 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 L☉) implies that He 3-1475 must be significantly more massive than a typical asymptotic giant branch star within the Galactic bulge, perhaps because of a past mass transfer and/or a merger event in an interacting binary system.