Radiative Transfer on Perturbations in Protoplanetary Disks

We present a method for calculating the radiative tranfer on a protoplanetarydisk perturbed by a protoplanet. We apply this method to determine the effecton the temperature structure within the photosphere of a passive circumstellardisk in the vicinity of a small protoplanet of up to 20 Earth masses. Thegravitational potential of a protoplanet induces a compression of the diskmaterial near it, resulting in a decrement in the density at the disk'ssurface. Thus, an isodensity contour at the height of the photosphere takes onthe shape of a well. When such a well is illuminated by stellar irradiation atgrazing incidence, it results in cooling in a shadowed region and heating in anexposed region. For typical stellar and disk parameters relevant to the epochof planet formation, we find that the temperature variation due to aprotoplanet at 1 AU separation from its parent star is about 4% (5 K) for aplanet of 1 Earth mass, about 14% (19 K) for planet of 10 Earth masses, andabout 18% (25 K) for planet of 20 Earth masses, We conclude that even suchrelatively small protoplanets can induce temperature variations in a passivedisk. Therefore, many of the processes involved in planet formation should notbe modeled with a locally isothermal equation of state.Comment: 23 pages, 8 figures (including 3 color figs). Submitted to Ap