The spectral energy distribution of self-gravitating protostellar disks

Abstract

Abstract. The long wavelength emission of protostellar objects is commonly attributed to a disk of gas and dust around the central protostar. In the first stages of disk accretion or in the case of high mass protostars, the disk mass is likely to be sufficiently large, so that the disk self-gravity may have an impact on the dynamics and the emission properties of the disk. In this paper we describe the spectral energy distribution (SED) produced by a simple, non-flaring, self-gravitating accretion disk model. Self-gravity is included in the calculation of the rotation curve of the disk and in the energy balance equation, as a term of effective heating related to Jeans instability. In order to quantify in detail the requirements on the mass of the disk and on the accretion rate posed on the models by realistic situations, we compare the SEDs produced by these models with the observed SEDs of a small sample of well-studied protostellar objects. We find that relatively modest disks -even lighter than the central star -can lead to an interesting fit to the infrared SED of the FU Orionis objects considered, while in the case of T Tauri stars the required parameters fall outside the range suggested as acceptable by the general theoretical and observational scenario. On the basis of the present results, we may conclude that the contribution of a selfgravitating disk is plausible in several cases (in particular, for FU Orionis objects) and that, in the standard irradiation, dominated disk scenario, it would help soften the requirements encountered by Keplerian accretion models.

Are quasars accreting at super-Eddington rates?

“…Another possibility is that in the remote regions of the disc (which are self-gravitating, see Collin & Huré 2001 for the Kaspi et al sample), selfgravitation induces changes in the rotation curve, which could become non-Keplerian. Such a mechanism has been proposed in the context of protostellar discs to explain their infrared spectrum (Lodato & Bertin 2001). Since these models are presently not sufficiently elaborated in the framework of AGN, we leave this question opened.…”

The vertical structure of T Tauri accretion discs

“…The excess in the far IR is a well-know feature likely due to some phenomenon occurring in the outer parts of the discs. For instance, Lodato & Bertin (2001) explain this excess with self-gravitation.…”

The vertical structure of T Tauri accretion discs

“…The disc is then more likely to depart from a symmetrical geometry and presents an additional dissipation of energy, hence an enhanced IR excess. Lodato & Bertin (2001) proposed this phenomenon to explain the far-IR excess among FUors. Phenomenon 1 is critical when determining the SED of a backwarmed disc.…”

“…In this case, self-gravity should mostly affect the coolest regions and therefore the SED at λ > ∼ 50 µm. Phenomena 2, 3 mostly affect viscous dissipation and can account for the far-IR SED for α ∼ 0.01 (Lodato & Bertin 2001). It is not impossible that the nature of the IR excess should be imputed to contributions of both backwarming and self-gravity.…”

“…e-mail: lachaume@mpifr-bonn.mpg.de Simon & Joyce 1988) as well as weak silicate feature at 10 µm sometimes present in emission (Hanner et al 1998); these properties seem more typical of an irradiated disc. Alternative models have tackled this problem: Lodato & Bertin (2001) showed that the self-gravity of the disc can trigger an instability that produces additional warming and were able to reproduce the SED. However, this model cannot account for the silicate feature, which requires a temperature inversion at the surface of the disc.…”