On the Luminosities and Temperatures of Extended X-Ray Emission from Planetary Nebulae

Noam Soker, Oranim, Tivon
Joel H. Kastner, Rochester Institute of Technology

© 2003 The American Astronomical Society

J.H.K. acknowledges support for this research provided by NASA/CXO grant GO0–1067X to RIT. N.S. acknowledges support from the US-Israel Binational Science Foundation.

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We examine mechanisms that may explain the luminosities and relatively low temperatures of extended X-ray emission in planetary nebulae. By building a simple flow structure for the wind from the central star during the proto, and early, planetary nebulae phase, we estimate the temperature of the X-ray emitting gas and its total X-ray luminosity. We conclude that in order to account for the X-ray temperature and luminosity, both the evolution of the wind from the central star and the adiabatic cooling of the post-shocked wind’s material must be considered. The X-ray emitting gas results mainly from shocked wind segments that were expelled during the early planetary nebulae phase, when the wind speed was moderate, ~500 km s^−1. Alternatively, the X-ray emitting gas may result from a collimated fast wind blown by a companion to the central star. Heat conduction and mixing between hot and cool regions are likely to occur in some cases and may determine the detailed X-ray morphology of a nebula, but are not required to explain the basic properties of the X-ray emitting gas (Refer to PDF file for exact formulas).