Accretion Disks with a Cloudy Sky-photon Floater
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Materials rotating above/below an accretion disk around a central object suffer from the influence of the strong radiation fields of the disk as well as the gravity of the central object. We find that there exists a critical floating height where the vertical gravity of the central object is balanced by the radiation force from the disk, and the materials are photon-floating there. The critical floating height is detemined by the disk effective luminosity Gamma_eff, which is defined by Gamma_eff = (sigma/sigma_T)(m_p/m)(L_d/L_E), where sigma and m are the material cross-section and mass, respectively, sigma_T and m_p the Thomson cross-section and the proton mass, respectively, and L_d and L_E the disk luminosity and the Eddington luminosity, respectively. For small Gamma_eff or large r (» z) the critical floating height Z_F is expressed as Z_F ～ 3 r_in_Gamma_eff, where r_in is the inner radius of the disk. The astrophysically important point is that this critical floating height is dynamically stable; hence, materials, such as gas clouds or dust or artificials, suffering from the radiation field of the disk drift toward this floating height. Such floating clouds - photon floaters - above/below the disk partially occults the disk. If the disk sky is cloudy, the observed luminosity becomes irregular. Futhermore, if a cloudy sky is present, the emitted spectrum would be remarkably modified due to reprocessing. A cloudy sky would also produce absorption/emission features. In addition, since the radiation from the disk is scattered by floating clouds at a critical floating height, the disk appears as if its thickness had become Z_F. The weather environment, such as a cloudy or dusty sky, changes the disk appearance significantly.
- Publications of the Astronomical Society of Japan
Publications of the Astronomical Society of Japan 48(1), 89-91, 1996-02-25
Astronomical Society of Japan