The Crab Nebula.
Abstract
Photographs of the Crab nebula, taken in selected regions of wave length, show that the nebulosity consists of two distinct parts, namely, an outer system of filaments and an inner mass of amorphous structure. Exposures in the Ha region lead to the conclusion that the line spectrum is localized in the envelope of filaments, the continuum in the inner amorphous mass. More than 80 per cent of the light of the nebula is contributed by the continuum. This high intensity can be understood only if the con- tinuum is interpreted as an emission spectrum. The star that excites the nebula cannot be conclusively identified at present. The north following component of the central double star is definitely ruled out. Proof that the south preceding component is the exciting star can be expected only after the proper motion of the nebula has been better de- termined. The present angular rate of expansion of the nebula is discussed. The value resulting from Duncan's measures appears to be too large, and the inferred acceleration of the expansion is probably spurious
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1942
- DOI:
- 10.1086/144446
- Bibcode:
- 1942ApJ....96..188B