Fig. 4.
Spectra (in velocity units) around Ca II λλ3934,3968. The spectrum in black centers on Ca II λ3934, whereas the spectrum in blue is centered on Ca II λ3968 and has been shifted +0.2 in relative flux units for clarity. The narrow, albeit unresolved, absorption close to zero velocity is interstellar absorption. No Ca II absorption originating in the Crab Nebula can be identified. Emission lines from the nebula (all from the nebula’s far side) have been marked.
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