Accretion disk models for FU Orionis and V1057 Cygni - Detailed comparisons between observations and theory

We present further tests of the accretion disk hypothesis for FU Orionis objects. Steady disk models that fit the broad-band energy distributions of V1057 Cyg and FU Ori require accretion rates of M ∼ 10 <SUP>-4</SUP> M<SUB>sun</SUB> yr<SUP>-1</SUP>, which implies that ∼ 10<SUP>-3</SUP> to 10<SUP>-2</SUP> M<SUB>sun</SUB> is added to the central object during an FU Orionis eruption. These models make reasonably quantitative predictions regarding the shape of absorption-line profiles and variation of rotation with wavelength using a small number of free parameters. Our analysis of intermediate and high- resolution observations shows good agreement with theoretical disk spectra. We estimate that the central stars have masses and radii (M<SUB>*</SUB> ∼ 0.3-1 M<SUB>sun</SUB>;R<SUB>*</SUB> ∼ 4 R<SUB>sun</SUB>) appropriate for normal pre-main-sequence stars if the inclination of the disk's rotation axis to the line of sight is i &lt; 30° for V1057 Cyg and 25° &lt; i &lt; 70&amp;deg for FU Ori. The monotonic fading of brightness of V1057 Cyg in the optical and near-infrared provides strong support for the accretion model. The lack of decline at 4.8 µm cannot be accounted for by steady disks, but may be a consequence of time-dependent phenomena in the evolving disk. Material in the outer disk appears to reprocess radiation emitted by the inner disk, and is responsible for the substantial far-infrared decay at 10-20 µm.

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