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Circumstellar and circumplanetary disks


Chiang, Eugene (2000) Circumstellar and circumplanetary disks. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/8B2W-8V06.


This thesis studies disks in three astrophysical contexts: (1) protoplanetary disks; (2) the Edgeworth-Kuiper Belt; and (3) planetary rings.

We derive hydrostatic, radiative equilibrium models of passive protoplanetary disks surrounding T Tauri and Herbig Ae/Be stars. Each disk is encased by an optically thin layer of superheated dust grains. This layer is responsible for up to ~70% of the disk luminosity at wavelengths between ~5 and 60 μm. The heated disk flares and absorbs more stellar radiation at a given stellocentric distance than a flat disk would. Spectral energy distributions are computed and found to compare favorably with the observed flattish infrared excesses of several young stellar objects. Spectral features from dust grains in the superheated layer appear in emission if the disk is viewed nearly face-on.

We present the results of a pencil-beam survey of the Kuiper Belt using the Keck 10-m telescope. Two new objects are discovered. Data from all surveys are pooled to construct the luminosity function from mR = 20 to 27. The cumulative number of objects per square degree, ∑(< mR, is such that log10∑(< mR = 0.52(mR - 23.5). The luminosity function is consistent with a power-law size distribution for which the smallest objects possess most of the surface area but the largest bodies contain most of the mass. To order-of-magnitude, 0.2Mⴲ and 1 x 1010 comet progenitors lie between 30 and 50 AU. The classical Kuiper Belt appears truncated at a distance of 50 AU.

We propose that rigid precession of narrow eccentric planetary rings surrounding Uranus and Saturn is maintained by a balance of forces due to ring self-gravity, planetary oblateness, and interparticle collisions. Collisional impulses play an especially dramatic role near ring edges. Pressure-induced accelerations are maximal near edges because there (1) velocity dispersions are enhanced by resonant satellite perturbations, and (2) the surface density declines steeply. Remarkably, collisional forces felt by material in the last ~100 m of a ~10 km wide ring can increase equilibrium masses up to a factor of ~100. New ring surface densities are derived which accord with Voyager radio measurements.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Circumstellar ; circumplanetary ; disks
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astronomy
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Goldreich, Peter Martin
Group:Astronomy Department
Thesis Committee:
  • Goldreich, Peter Martin (chair)
  • Phinney, E. Sterl (co-chair)
  • Sargent, Anneila Isabel
  • Blake, Geoffrey A.
  • Brown, Michael E.
Defense Date:11 May 2000
Record Number:CaltechETD:etd-09172008-151500
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3600
Deposited By: Imported from ETD-db
Deposited On:05 Nov 2008
Last Modified:21 Dec 2019 04:43

Thesis Files

PDF (Chiang_e_2000.pdf) - Final Version
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