Dust Particles and Molecules in the Extended Atmospheres of Carbon Stars

Abstract

It is shown that the absorption due to a circumstellar shell containing solid silicon carbide particles can very nicely explain the observed strong violet opacity in stars in which the carbon to oxygen ratio is > 1. It has been shown by Friedemann and Gilman that solid SiC particles can form in the cooler outer layers of such stars. Thermal re-emission from SiC particles is predicted to be in the 10–13 μ region and recent infrared observations by Hackwell show an emission band in this region, thereby strongly supporting the SiC suggestion. It is also shown that the opacity due to C3 pseudo-continuum is not adequate to explain the observed violet opacity.It is suggested that the vibrational bands of C3 and SiC2 molecules should be among the major opacity sources in the infrared spectra of the late N-type carbon stars and some of the observed bands may be, at least in part, due to these molecules. The frequencies of their isotopic species have been calculated and attempts should be made to observe these bands.Thus the atmosphere of a late N-star should be pictured as containing, probably on its outskirts, solid carbon particles. There is some kind of smoke veil around the star causing a reddening by absorption of the ultraviolet.A veiling effect by smoke has been occasionally envisaged to interpret various astronomical phenomena, even in the case of novae. A late N-star would be a striking example. The smoke veil would vary in variable N-stars.B. Rosen and P. Swings (1953)