Abstract
IN an interesting note by C. T. Elvey (NATURE, 121, p. 12, Jan. 7, 1928) a calculation has been given of the “density necessary to produce the nebulium spectrum,” the example considered being the nebulosity originating in the new star Nova Aquilæ, 1918. The outburst of this star was observed early in June 1918; by October a bright nebulous envelope had appeared around the star; it continued to spread as long as the star was under spectroscopic observation (August 1926). The outward flying gases had an average velocity of some 2000 km./sec. The N1 and N2 lines (5007 A. and 4959 A.) were recognised in the spectrum about 19 days after the outburst. At that time the density of the envelope would be of about 10-17 grams/c.c. In the first years of the existence of the envelope the light of the gas consisted mainly of the nebulium lines N1 and N2; in 1926, however, these were extremely faint, and most of the light came from the Balmer lines of hydrogen and 4686 A. He+ (E. Hubble and J. C. Duncan, Astrophys. J., 66, p. 60; 1927 ; and Plate IV.). Nine other novæ give similar density, 10-19 to 10-20 grams/c.c, that is, about 50 molecules/c.c.
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MCLENNAN, J., RUEDY, R. The Nebulium Spectrum. Nature 121, 319 (1928). https://doi.org/10.1038/121319a0
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DOI: https://doi.org/10.1038/121319a0
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