Dissertation > Excellent graduate degree dissertation topics show

Research on Episodic Accretion in Magnetically Layered Protoplanetary Discs

Author: FangNa
Tutor: JinLiPing
School: Jilin University
Course: Theoretical Physics
Keywords: Accretion disk Protoplanetary disk Magnetization stratified protoplanetary disks Gravitational instability Magnetic rotary instability
CLC: P14
Type: Master's thesis
Year: 2011
Downloads: 5
Quote: 0
Read: Download Dissertation

Abstract

The solar nebula Theory is currently the most widely accepted theory of origin of the solar system. The interstellar gas cloud caused because the gravitational collapse of a nearby supernova explosion pressure brought molecular cloud cores collapse to form a protostar contraction from the inside out, and more, in order to ensure the conservation of angular momentum, external rotating nebula around the protostar movement the faster settlement of the substance to the mid-plane, the the nebula structure becomes increasingly flat, and ultimately the formation of the structure of the protostellar disk. The center of the protostar continues to evolve into accreting matter from the disk of the sun now; the intraday gas - dust caking settlement accumulate slowly evolved to form the size of celestial bodies around the Sun. This disc structure is pregnant with the growth of the planet, the solar nebula, also known as the protoplanetary disk. Protoplanetary disk is an accretion disk around stellar movement. Study the origin of the solar system, starting from the theoretical basis of the accretion disk, build a more realistic model of a protoplanetary disk, the process and the results of the numerical simulation of its evolution, in order to explain the solar system available observations, can also predict future phenomena. Numerical calculation of the evolution of the protoplanetary disk, the main parameters of the surface density of the accretion rate, viscosity coefficient, temperature, Q parameters. The numerical calculation magnetization concluded that in order to explain the astronomical phenomenon layered protoplanetary disk accretion rate changes. The uniform viscous full viscous disk, the numerical simulation of the solar nebula evolution, seems to have missed a lot of information and missing some important results. In 1996, Professor Jin Liping first magnetization layered protoplanetary disk structure to explain the existence of the \thick and can not be cosmic rays penetrate the gas is very low degree of ionization, the magnetic rotary instability (MRI) is insufficient to maintain the lower this area viscous α; InR the surface region and the outer region of the plate, since the gas sparse can be universe ray penetration, the degree of ionization is sufficient to maintain MRI; the dish interior region (IR) temperature greater than 800K, due to thermal ionization, MRI can be maintained. Armitage, in 2001, the use of magnetization layered disc model to describe the protoplanetary disk, consider 1AU radius near the quiet layer of local GI trigger to transfer angular momentum to simulate viscosity coefficient alpha, found that the accretion rate there will be the occasional high suction the outbreak of the accretion rate. This leads to a strong mass outflow of young stellar objects appear repetitive. This accretion mode should appear early in the evolution of protoplanetary disks around less than 1 million years, then layered intraday low average accretion rate of many young main-sequence star early, it follows: when the plate the scale scale far exceeding the minimum mass solar nebula (about a few hundred million years of evolutionary time), quality of tiered tray plate quality than the viscous disk plate about 10 times larger, and most of the extra quality will accumulate in the radius the 1AU near quiet layer. The layered disk quiet layer viscous smaller low mass planet migration rate in the outer edge of the layered disc is reduced, which also increases the giant planets is a possibility of the formation in the area of ??a radius of 1-3AU. Magnetization layered Armitage (2001), based on the study of the inner boundary of the protoplanetary disk accretion rate. The main innovations: 1) layered disk model, consider the global GI to transfer angular momentum. Article that the surface density of the plates at any radius larger than the critical value, GI appears; then the whole plate is in a highly viscous state, and having a large α value. Local processing mechanism with large radius compared to the global processing methods increase the probability of occurrence of GI. 2) different processing method of the non-uniform viscous. GI appears, this paper set the viscous parameter of 0.02; related to the size of the viscous parameters and local gravitational surface density and local processing. GI subsided paper complex alpha value, there is a difference between setting parameters used and Armitage. Therefore, the low value accretion rate steady change, rather than a stable value. This paper argues that the plates outside a stable quality into the ring (?) _Infall added to the plate, the dish from the quality zero evolution to a steady state or steady state limited circulation state. In the initial conditions, the use of the global the GI trigger the mechanism and the non-uniform viscous to seek the numerical solution of substances the accreting protostar accretion rate (the inner boundary of the accretion rate). Quality into the set value in a certain range of time, numerical results also appear high accretion rate occasional outbreak phenomenon: the GI appears corresponds to the peak of about 3 ^{-6 M _⊙ yr ^{( -10, GI subsided corresponding low value of about 10 ^{-10 M _⊙ yr ^{-1 , both alternating this explosive phenomenon explains the young stars frequently appear periodically outwards quality jet, calculated as the observed pulse. \the ^{3 yr, this time more than the result of local 10 ^{4 yr smaller jet with FU Orionis stars quality observations compare, more in line with the results of this paper. In fact, the quality of the size of the inflow affect the outbreak continued as well as the recurrence of time. Usually, the mass flows to set smaller the value, the shorter the duration of outbreak peak sharper images, and the re-emergence of the longer. addition, of layered protoplanetary disk in magnetized the quiet layer region, mobility reduce massive planets have a certain amount of time and plate interactions have a greater eccentricity.}}}}}}

Research on Episodic Accretion in Magnetically Layered Protoplanetary Discs

Abstract

Related Dissertations