Effects of back warming in cocoon stars

Abstract

THERE now exists general agreement among astronomers that dust shells surrounding young stars are a relatively frequent occurrence, and attempts have been made to calculate some of the properties of such shells (see refs 1 and 2). One obvious possibility is that the dust absorbs the outgoing radiation from the star and re-emits it in the infrared, and this is perhaps the most acceptable explanation for a number of the infrared sources that have been detected in the Orion nebula and in other regions where star formation is suspected to be occurring. If the dust shell absorbs any radiation, then both its inner and outer surfaces will re-emit a certain proportion, though now at a different wavelength, so that some radiation will return to the central star—it is ‘warming its own back’ so to speak. It is interesting to ask how such a star will evolve when compared with the evolution of a normal pre-main-sequence star. A model for a contracting star which is receiving radiation from an external source has already been developed by the authors³ in connection with the evolution of Jupiter within the radiation field of the Sun, and here we apply this model to the situation just described.