Infrared Space Observatory Polarimetric Imaging of the Egg Nebula (RAFGL 2688)

Joel H. Kastner, Rochester Institute of Technology
Jingqiang Li, Rochester Institute of Technology
Ralf Siebenmorgen, European Southern Observatory
David A. Weintraub, Vanderbilt University

© 2002 The American Astronomical Society.

The authors thank Mark Morris and Raghvendra Sahai for the use of their 8.8 µm Keck image of RAFGL 2688. CIA is a joint development by the ESA Astrophysics Division and the ISOCAM Consortium. The ISOCAM Consortium is led by the ISOCAM PI, C. Cesarsky. ISO research by JHK and JL was supported by JPL grants 1230950 and 1211136 to RIT.ISSN:1538-3881

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We present polarimetric imaging of the protoplanetary nebula RAFGL 2688 obtained at 4.5 µm with the Infrared Space Observatory (ISO). We have deconvolved the images to remove the signature of the point spread function of the ISO telescope, to the extent possible. The deconvolved 4.5 µm image and polarimetric map reveal a bright point source with faint, surrounding reflection nebulosity. The reflection nebula is brightest to the north-northeast, in agreement with previous ground- and space-based infrared imaging. Comparison with previous near-infrared polarimetric imaging suggests that the polarization of starlight induced by the dust grains in RAFGL 2688 is more or less independent of wavelength between 2 µm and 4.5 µm. This, in turn, indicates that scattering dominates over thermal emission at wavelengths as long as ~5 µm, and that the dust grains have characteristic radii < 1 µm.