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Nature volume 101, page 114 (11 April 1918) | Download Citation

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Abstract

SPECTRUM AND RADIAL VELOCITY OF N.G.C. 1068.—Further photographic observations of the spectrum of the spiral nebula N.G.C. 1068 (M77) have been made at Flagstaff by Dr. V. M. Slipher (Lowell Observatory Bulletin, No. 80). Among the photographs obtained was one taken with a two-prism spectrograph, which received a total exposure of thirty-five hours during five nights. Besides confirming the composite character of the spectrum and the high velocity previously recorded, this photograph shows that the bright hydrogen lines extend farther into the fainter parts of the nebula than do the two green nebular lines, and that both bright and dark lines are strongly inclined. The inclination is about 5°, and indicates a rotation about an axis through the shorter diameter of tfre nebula, the velocity of rotation being approximately 300 km. per sec. at i′ from the nucleus. This is the highest rotational speed which has yet been recorded, and there is evidence that the inner part is turning into the arms of the spiral, like a winding spring, as in the case of other spirals in which rotation has been observed. A peculiar feature of the emission lines is that instead of appearing as simple images of the slit, they appear as small discs; pressure increasing towards the nucleus is a possible explanation. The recent photographs consistently indicate the enormous receding velocity of 1120 km. per sec. for this nebula.

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https://doi.org/10.1038/101114a0

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