Astrophysical interpretation of the lam lam 1200-7300 angstrom emission line spectrum of a filament in the CYG Loop Supernova remnant.

Abstract

An IUE spectrum of a filament in the Cygnus Loop supernova remnant obtained with the low resolution, long wavelength camera, has been combined with earlier far UV and optical data to obtain a complete spectral coverage between 1200 and 7350 Å. The observed continuum is fully understood as a combination of free-free emission, recombination and hydrogen two photon emission, reinforced by collisional excitation to the 2S½ level.

The emission lime spectrum is, in general, well interpreted in the framework of a shockwave model of moderate velocity (v_s=90 km/s) and depleted abundances.

The unexpected weakness of the C II λ1335 Å line may be due to scattering in the filament seen as an edge on sheet, or, less likely, owing to absorption in the intervening interstellar medium, indicates a column density of interstellar C II of ≃2.5 × 10¹⁴ cm^-2 toward the remnant.