Temperature inversion on the surface of externally heated optically thick multigrain dust clouds

Abstract

It was recently discovered that the temperature in the surface layer of externally heated optically thick gray dust clouds increases with the optical depth for some distance from the surface, as opposed to the normal decrease in temperature with distance in the rest of the cloud. This temperature inversion is a result of efficient absorption of diffuse flux from the cloud interior by the surface dust exposed to the external radiation. A micron or bigger size grains experience this effect when the external flux is of stellar spectrum. We explore what happens to the effect when dust is a mixture of grain sizes (multigrain). Two possible boundary conditions are considered: i) a constant external flux without constrains on the dust temperature, and ii) the maximum dust temperature set to the sublimation temperature. We find that the first condition allows small grains to completely suppress the temperature inversion of big grains if the overall opacity is dominated by small grains. The second condition enables big grains to maintain the inversion even when they are a minor contributor to the opacity. In reality, the choice of boundary condition depends on the dust dynamics. When applied to the physics of protoplanetary disks, the temperature inversion leads to a previously unrecognized disk structure where optically thin dust can exist inside the dust destruction radius of an optically thick disk. We conclude that the transition between the dusty disk and the gaseous inner clearing is not a sharp edge, but rather a large optically thin region.

8 pages, 10 figures, Accepted for publication in the Astrophysical Journal

References in corpus (8)

• Passive irradiated circumstellar disks with an inner hole
• Flaring vs. self-shadowed disks: the SEDs of Herbig Ae/Be stars
• The Shape of the Inner Rim in Proto-Planetary Disks
• On the Interferometric Sizes of Young Stellar Objects
• The 2-D structure of dusty disks around Herbig Ae/Be stars, I. Models with grey opacities
• Near infrared and the inner regions of protoplanetary disks
• Efficient radiative transfer in dust grain mixtures
• Effects of Grain Size on the Spectral Energy Distribution of Dusty Circumstellar Envelopes

Cited by in corpus (13)

• The inner regions of protoplanetary disks
• Relation between the luminosity of young stellar objects and their circumstellar environment
• Radiation pressure mixing of large dust grains in protoplanetary disks
• The Diversity of Planetary Systems Architectures: Contrasting Theory with Observations
• Planet Formation: Statistics of spin rates and obliquities of extrasolar planets
• The role of the initial surface density profiles of the disc on giant planet formation: comparing with observations
• Aperture Synthesis Imaging of V892 Tau and PV Cep: Disk Evolution
• Inner dusty regions of protoplanetary discs -- II. Dust dynamics driven by radiation pressure and disc winds
• Mid-infrared interferometric variability of DG Tau: implications for the inner-disk structure
• Constraints on the height of the inner disk rim in pre-main-sequence stars
• Inner dusty regions of protoplanetary discs - I. High resolution temperature structure
• Inner dusty regions of protoplanetary discs -- III. The role of non-radial radiation pressure in dust dynamics
• Mid- and Far-Infrared Variability of PV Cep