Multi-Slit MMT Spectroscopy of Peculiar Knots in the Crab Nebula
Session 56 -- Supernova Remnants Observation
Display presentation, Thursday, 2, 1994, 9:20-6:30

[56.05] Multi-Slit MMT Spectroscopy of Peculiar Knots in the Crab Nebula

Stephen S. Lawrence, Gordon M. MacAlpine (Univ. of Michigan)

Spectroscopy of ten semi-stellar, line-emitting knots in the Crab Nebula has been obtained using multi-slit aperture plates at the Multiple Mirror Telescope. Wavelength coverage is 3500--8200~\AA, with a velocity resolution of approximately 250~km~s$^{-1}$. These knots are strikingly aligned in arcs extending to the north and south from the pulsar. Their spectra are highly atypical for Crab Nebula filamentary gas, showing anomalously strong lines from collisionally excited, heavy elements. In particular, these knots tend to have significantly stronger [S II]~$\lambda \lambda$~6717, 6731 and [Ar III]~$\lambda\lambda$~7136, 7751 emissions relative to H$_{\beta}$, as compared to surrounding filaments. We discuss the roles of temperature, ionization, and chemical abundances for producing the anomalous spectra, and also the implications for the nature of these knots and their relationship to the pulsar.