Can envelope backwarming of discs explain mm-bright, extended protostellar structures?

Abstract

ABSTRACT We construct simple models to explore in principle whether the backwarming by radiation from infalling envelopes can significantly heat and change the structure of protoplanetary discs. The motivation for this investigation is the recent study of a small subset of Orion protostars by Karnath et al., who argued that the bright, extended, and irregular sub-mm and mm emission did not arise from protostellar discs because the images were not elongated as expected. We therefore constructed simple disc models to see whether heating from the envelope surrounding a disc could in principle significantly increase disc scale heights and thus produce less-elongated images. We assume steady accretion and solve the radiative transfer self-consistently. For central luminosities and envelopes roughly comparable to the Karnath et al. protostars, we find that while envelope irradiation can significantly heat the discs, the magnitude of the effect only increases scale heights by modest factors, and so our models cannot easily account for the observed morphologies. We speculate that dynamical perturbations by companion protostars might be responsible for the observed complex structure.