The Nebulium Spectrum in New Stars

Abstract

IN a recent communication (NATURE, Jan. 7, p. 12) C. T. Elvey has applied the ‘expanding shell’ theory of novæ to calculate the maximum density at which oxygen can be made to give the nebulium spectrum. In Nova Aquilæ, No. 3 (discovered June 8, 1918), the line λ5007 was first seen on June 27, when its breadth was 55 A.; and the gases are therefore assumed to have been travelling outwards for 19 days with a velocity of 1700 km./sec. before reaching a low enough density to emit this line. If, then, the phenomena are due to the reversing layer of the star being blown off bodily as a shell of gas, we can find the density in the shell at any moment after the outburst, given the initial density and radius. Elvey finds in this way that at the first appearance of the nebulium lines the gas must have a density of the order 10^-17 gm./c.c.