Year: 1945
Type: article
Abstract: The deep minimum in the light-curve, which appeared in the transition stage of Nova Herculis 1934 and Nova Cygni 1942, was accompanied in both cases by the weakening of the continuous spectrum, the suppression of the absorption spectrum and of the bright bands of C II, N II, O II emitted by a shell of late origin. The violet maxima of the bright bands of H , Fe II, Ca II from the earlier or outer shell strengthened and moved out to cover the positions previously occupied by the corresponding absorption lines; the red maxima weakened or vanished. An explanation is offered in terms of an opaque cloud forming inside the outer shell passing across the central star, obscuring it and the inner shells. This implies that the later shells do not move out with the velocities of the spectroscopically observable atoms that traverse them. Similar conclusions were reached by Tai in the case of Nova Herculis from a study of the contours of lines showing double absorptions. A study of Nova Persei 1901 also supports the view that the speed of outward spread of visible shells is less than the velocity of atoms passing through them. Comparison is made with changes of spectrum found at the minima in the stage of fluctuating luminosity of fast novæ. The source of the surviving continuous spectrum is uncertain. The view that it is due to reflected light from portions of the outer shell still illuminated by the central star gains support from the spectrum of Hubble's variable nebula. No final explanation is offered on the nature of the obscuring cloud, but some connection with the outflowing atoms of carbon, nitrogen and hydrogen is suggested.
Author: F. J. M. Stratton
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2003186229