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

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Session 62 -- Supernova Remnants and Pulsars
Oral presentation, Tuesday, 10, 1995, 10:00am - 11:30am

[62.01D] Fabry-Perot Imaging Spectroscopy of the Crab Nebula, Cassiopeia A, and Nova GK Persei

S. S. Lawrence, G. M. MacAlpine (U. Michigan), A. Uomoto (Johns Hopkins), B. E. Woodgate (NASA/GSFC)

Three-dimensional spatial models of the line-emitting gas in the Crab Nebula, Cassiopeia~A, and Nova GK~Persei have been developed from imaging spectroscopy taken with the Goddard Fabry-Perot Imager (GFPI) at Michigan-Dartmouth-MIT Observatory (MDM). The spatial model of the Crab Nebula in \hbox{[O\hskip 2trueptIII]}~$\lambda$5007 reveals the relationship between the ``high-helium torus'' and the north-south bipolar asymmetry of the remnant shell, the size of the inner synchrotron cavity, and holes near the ends of the major optical axis. Images of the fast-moving knots of Cas~A in \hbox{[S\hskip 2trueptII]}~$\lambda\lambda$6716,~6731 provide a more complete view of the three-dimensional morphology of the remnant. The bright northern arch is actually two kinematically distinct rings; the larger contains the most highly redshifted material in the nebula and many of the newly-formed \hbox{[O\hskip 2trueptIII]} knots. The most blueshifted material occurs in patchy nebulosity to the southeast. The data for the quasi-stationary flocculi of Cas~A in H$_{\alpha}$ $+$ \hbox{[N\hskip 2trueptII]}~$\lambda\lambda$6548,~6583 reveal new nebular features and show an elliptical distribution on the sky. Isophotes of the remnant of nova GK~Persei in H$_{\alpha}$ $+$ \hbox{[Ni\hskip 2trueptII]} show a lack of emission in the forward, northeastern zone, suggest the presence of a bulge-like structure in the south-southeast, and indicate recent strengthing in the northeastern limb.

Extraordinary, compact, line-emitting knots are apparent in images of the Crab Nebula obtained with the GFPI at MDM. The knots appear most prominently in \hbox{[O\hskip 2trueptIII]}~$\lambda$5007 through a 5.3~\AA ~(FWHM) bandpass at 5015.3~\AA, with fluxes of order 10$^{-14}$~erg~cm$^{-2}$~s$^{-1}$. They are aligned in arcs, seven to the north and four to the south, from the pulsar. Measurements over a two-year baseline yield proper motions $\la$0\farcs 1~yr$^{-1}$ ($\la$900~km~s$^{-1}$ at 1800~pc). Spectroscopy from MDM and the Multiple Mirror Telescope shows that the knots are characterized by remarkably strong \hbox{[Ar\hskip 2trueptIII]}~$\lambda$7136 emission, possibly indicating high argon abundances or unusual excitation mechanisms; high gas temperatures are excluded.

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