Three-Dimensional Fabry-Perot Imaging Spectroscopy of the Crab Nebula, Cassiopeia A, and Nova GK Persei

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Abstract

Three-dimensional spatial models of the line-emitting gas in the Crab Nebula, Cassiopeia A, and the nova remnant of GK Persei have been developed from imaging spectroscopy taken with the Goddard Fabry- Perot Imager mounted on the McGraw-Hill 1.3 m and Hiltner 2.4 m telescopes of the Michigan-Dartmouth-MIT Observatory. The spatial model of the Crab Nebula in [O III] λ5007 emission reveals the thin, annular morphology of the "high-helium torus," the association of this torus and other bright filament loops with north-south bipolar asymmetry of the remnant shell, the structure of the filamentary shell at the boundary with the inner synchrotron cavity, and holes in the distribution of the brightest filaments at the ends of the major optical axis. Images of the fast-moving knots in Cas A in [S II] λλ6716, 6731 emission extend deeper than previously published broadband images, providing a more complete view of the limb-brightened, spherical edge of the remnant. The bright northern arch is imaged as two continuous rings of material distinct in velocity space. The larger ring includes the most highly redshifted material detected in Cas A, and incorporates many of the newly formed [O III] knots. The most blueshifted material occurs in the patchy nebulosity in the southeastern region of the remnant, and a large velocity asymmetry is seen in the radial and spatial velocities of the most highly blueshifted and redshifted optical knots. The data cube for the quasi-stationary flocculi in Cas A in Hα+ [N II] λλ6548, 6583 emission reveals more diffuse nebulosity than previously detected and shows a distribution contained within an elliptical region on the sky which extends well beyond the spherical distribution of FMKs. Isophotes of GK Per in Hα+[N II] λλ6548, 6583 emission demonstrate the "boxiness" of the remnant as projected on the sky, show a lack of emission in the northern "front" and eastern "central" portions of the nebula, suggest the presence of a bulge-like structure in the south-southeast, and may indicate recent strengthening of emission in the northeastern limb.

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