We present high spectral resolution maps of near-infrared molecular hydrogen emission from the bipolar pre-planetary nebulae RAFGL 2688 and RAFGL 618, obtained with the NOAO Phoenix spectrometer. The measured velocity gradients along the polar axes of both nebulae indicate that the highest velocity gas lies closest to the central stars. These results support the suggestion that the polar H2 emission regions of both nebulae contain shocked gas formed as fast (~50−150 km s^−1), collimated, post-asymptotic giant branch (AGB) winds collide with slower-moving (~10−20 km s^−1) material previously ejected while the central stars were still on the AGB. The kinematics of H2 emission perpendicular to the polar axis of RAFGL 2688 are consistent with a model combining expansion along the equator at 5−10 km s^−1 with rotation about the polar axis at 5−10 km s^−1. The rapid onset of the common envelope phase of a close binary system may explain both the bipolar structure of RAFGL 2688 and the presence and complex kinematics of its shocked H2 emission (Refer to PDF file for exact formulas).

Publication Date



© 2001 The American Astronomical Society

Support for this research was provided in part by a JPL/ISO grant to R. I. T. We acknowledge enlightening discussions with Adam Frank and Robert Lucas and the helpful comments of the referee.ISSN:1538-4365 Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.

Document Type


Department, Program, or Center

School of Physics and Astronomy (COS)


RIT – Main Campus