Abstract
IN a recent letter to NATURE (Jan. 7, p. 12) C. T. Elvey attempts to calculate the density, ρ, of the expanding gaseous shell of a nova at the moment when the nebular lines first appear. It is easily shown that ρ = ρ0r02/v2t2 where ρ0 is the original density of the shell when coincident with the stellar atmosphere, r0 its original radius, v its velocity of expansion, and t the time elapsing between the outburst and the appearance of the nebular lines. The above equation involves the additional and somewhat questionable assumption that the thickness of the expanding shell does not change. Elvey takes v from velocity displacements on nova spectrograms. For Nova Aquilæ 3 this is about 1700 km./sec. and t=19 days. Hence he finds,
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Russell, Dugan, and Stewart, œAstrophysics and Stellar Astronomy,p. 835.
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MENZEL, D. The Density necessary to Produce the Nebular Spectrum. Nature 121, 618 (1928). https://doi.org/10.1038/121618a0
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DOI: https://doi.org/10.1038/121618a0
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