Yang Lan-tian

Wave Propagation in Accretion Disks with Self-Gravity

We extend the research by Lubow and Pringle of axisymmetric waves in accretion disks to the case where self-gravity of disks should be considered. We derive and analyse the dispersion relations with the effect of self-gravity. Results show that self-gravity extends the forbidden region of the wave propagation: for high frequency p-modes, self-gravity makes the wavelength shorter and the group velocity larger; for low frequency g-modes, the effect is opposite.

Radial self-gravity of accretion disc around supermassive black holes

This paper studies the properties of self-gravity of accretion discs around supermassive black holes. With integration on the thin disc configuration, this paper has calculated the radial and vertical components of self-gravity of accretion discs. The discussion mainly concentrates on the radial component, and the results are briefly as follows: ‘for accretion discs around supermassive black holes (M∼108–1010 M⊙). At the distance where (R/Rg)∼105–104, the radial component of self-gravity dominates over the central one where the dynamical structure of the accretion discs completely differs from that of Keplerian disc. A turbulence driven by radial self-gravity instability as a kind of energy source is proposed. This paper has two criteria for the comparison of magnitude between the self-gravity of accretion discs and the gravity of the central black hole, from which an analytic estimation for the outer radius of the accretion discs has been derived. The results of this paper may be used to explain the accretion discs of quasars and AGNs.

On the pulsational-radial oscillations instability of isothermal magnetized accretion disk with self-gravity

This is the first paper to consider the effects of both magnetic field and self-gravity on the pulsational instability. Our main new results are that the self-gravity enhances the instability of the magneto-acoustic mode in the outer disk strongly, and also affects the instability in the inner disk, but stabilized the viscous mode. The effect of self-gravity is much greater than that of magnetic field in the outer disk, while the effect of magnetic field on the instability is weaker than that in the previous works (Wuet al., 1995; Yanget al., 1995), in which the self-gravity has not been considered. Finally, we discuss our results.

A determination of the K-correction for quasars

Abstract The K -correction is made up of an emission line component and a continuum component. These two components are iteratively determined in this paper from line widths and intensities, redshifts, U , B , V colours and radio spectral indices for 355 quasars. The colors B - V and U - B , corrected for the emission line portion of the K -correction, are plotted against Z , giving 2 mean relations. Eliminating Z between these gives a mean optical continuum, which is then used to calculate the continuum portion of the K -correction.

Axisymmetric Waves in Isothermal Accretion Discs with Vertical Self-Gravity*

We extend the research of axisymmetric waves in accretion discs with three-dimensional structure to the case that vertical self-gravity of the discs is included. We derive and analyze the dispersion relation and solve the eigenfunctions numerically. The following results have been reached: vertical self-gravity expands the forbidden region of the wave propagation. As the influence of the vertical self-gravity increases, the group velocities of the waves get smaller and the vertical nodes of the wave shrink to the middle plane of the disc.

Stability of an Isothermal Disk with Three-Dimensional Magnetic Fields and Radial Viscous Force*

The stability of an isothermal thin disk with three-dimensional magnetic fields and radial viscous force is examined in this paper. We find that the radial viscous force has no influence on the stability of viscous modes. But there is more influence on the stability of magneto-acoustic modes, which is related to the perturbation wavelength and different parts of disk. Finally, we use our model to explain the long-term variability of Quasar 3C345.

The Radial-Azimuthal Instability of a Radiation-Pressure-Dominated Accretion Disk with Advection*

A radial-azimuthal instability analysis of a radiation-pressure-dominated accretion disk with advection is presented. We find that the including of a very little advection has significant effect on two acoustic modes, which are no longer complex conjugates of each other. With the increase of azimuthal perturbations, the thermal mode becomes more unstable and the viscous mode more stable, but there has no effect on acoustic mode. For geometrically slim and advection-dominated disks, the azimuthal perturbation and increasing of advection do not affect the stability of all the modes.

The Radial-Azimuthal Instability of Gas-Pressure-Dominated Accretion Disk with Advection

The radial-azimuthal instability of gas-pressure-dominated accretion disk with advection is examined in this paper. We find that the including of very little advection has significant effects on two acoustic modes, which are no longer complex conjugates of each other. They increase the instability of the O-mode and damp that of the I-mode. We also find that when the azimuthal perturbations are considered, the stability properties of disk are different from that in pure radial perturbation case. The increase of azimuthal wave number will stabilize the acoustic modes but make the viscous mode more unstable and does not change the thermal mode very much for optically thin disk. The I-mode is more stable. The O-mode, viscous mode and thermal mode tend to become more unstable with the increase of azimuthal perturbation wavenumber for optically thick disk. For a geometrically slim, advection-dominated disk, the increasing of azimuthal perturbations make thermal mode more unstable and acoustic mode more stable.

The Pulsational Instability of Non-Isothermal Magnetized Accretion Disk with Self-Gravity in the Transition Zone*

By analyzing the fifth-order dispersion relation, the influence of coupled magnetic field and self-gravity on the pulsational instability of gas pressure dominated accretion disk is investigated. Our main results are that the viscous modes become more stable with the increase of self-gravity, magnetized field and viscosity, while they enhance the instabilities of acoustic modes. The effect of self-gravity to the instability is much greater than that of magnetic field in transition zone of the accretion disk. Especially, the self-gravity affects the thermal-modes and acoustic modes strongly. Finally, we discuss our results.

The radial-azimuthal instability of an isothermal magnetized accretion disk

The radial-azimuthal instability of an isothermal magnetized accretion disk is examined in this paper. We find that the azimuthal perturbation enhances the instability of the magneto-acoustic and non-axisymmetric modes. The magnetic field induces and enhances the instability of magneto-acoustic modes, but stabilizes the non-axisymmetric modes in the outer disk. The viscous modes are always stable. The instability of magneto-acoustic modes are dominant in this disk.