2007/07/23 by Zhaohuan Zhu, Lee Hartmann, Nuria Calvet +5 · 10 citations
Chemistry · Physics and Astronomy · #Accretion (finance) #Astro and Planetary Science #Astrophysics #Astrophysics and Star Formation Studies #Debris disk #Extinction (optical mineralogy) #Galaxy #Instability #Magnetohydrodynamics #Magnetorotational instability #Mechanics #Physics #Planet #Planetary system #Plasma #RADIUS #Radiative transfer #Spectroscopy and Laser Applications #Spitzer Space Telescope #Stars #Thick disk #Thin disk #astro-ph
paper · pdf · doi:10.1086/521345
32 pages, 10 figures, to appear in the Astrophysical Journal
arxiv created 2007/07/23 · openalex publication_date 2007/11/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We have constructed a detailed radiative transfer disk model which reproduces the main features of the spectrum of the outbursting young stellar object FU Orionis from ~4000 Å to ~8 μm. Using an estimated visual extinction A V ~ 1.5, a steady disk model with a central star mass ~0.3 M ☉ , and a mass accretion rate ~2 × 10 -4 M ☉ yr -1 , we can reproduce the SED of FU Ori quite well. Higher values of extinction used in previous analysis ( A V ~ 2.1) result in SEDs which are less well fitted by a steady disk model, but might be explained by extra energy dissipation of the boundary layer in the inner disk. With the mid-infrared spectrum obtained by the IRS on board the Spitzer Space Telescope , we estimate that the outer radius of the hot, rapidly accreting inner disk is ~1 AU, using disk models truncated at this outer radius. Inclusion of radiation from a cooler irradiated outer disk might reduce the outer limit of the hot inner disk to ~0.5 AU. In either case, the radius is inconsistent with a pure thermal instability model for the outburst. Our radiative transfer model implies that the central disk temperature T c ≥ 1000 K out to ~0.5-1 AU, suggesting that the magnetorotational instability can be supported out to that distance. Assuming that the ~100 yr decay timescale in brightness of FU Ori represents the viscous timescale of the hot inner disk, we estimate the viscosity parameter to be α ~ 0.2-0.02 in the outburst state, consistent with numerical simulations of the magnetorotational instability in disks. The radial extent of the high- region is inconsistent with the model of Bell & Lin, but may be consistent with theories incorporating both gravitational and magnetorotational instabilities.