PhD Thesis Defenses: 2003
- June 2003
- June 26, 2003
Thomas Crawford: Mapping the Southern Polar Cap with a Balloon-borne Millimeter-wave Telescope
TopHat is a balloon-borne millimeter-wave telescope designed to make a map of a 48�-diameter region centered on the South Celestial Pole. The instrument consists of telescope optics, radiometer, rotational drive system, sun/earth shield, attitude and thermal sensors, and support electronics mounted on top of a 28-million cubic foot balloon, with a support gondola hanging below. The five-channel, single- pixel radiometer sits at the focus of an on-axis Cassegrain telescope with a 1-meter primary aperture. The detectors are monolithic, ion-implanted silicon bolometers, cooled to 265 mK by a sorption-pumped helium- 3 fridge. The five frequency bands have effective centers of 175, 245, 400, 460, and 630 GHz. The two lowest- frequency bands are designed to be sensitive to the 2.7 K Cosmic Microwave Background (CMB), while the three highest bands are designed to monitor thermal emission from interstellar dust grains. Together with a modified Winston cone at the Cassegrain focus, the telescope optics define a beam designed to be steeper than gaussian with a full-width at half-maximum of 20', rendering TopHat in principle sensitive to fluctuations in the CMB from scales of less than a degree up to the diameter of the map (6 ≤ ℓ ≤ 600). TopHat was launched on 4 January 2001 from McMurdo Station, Antarctica as part of the NASA National Scientific Balloon Facility (NSBF) Polar Long-Duration Balloon program and observed for four sidereal days until cryogens were exhausted. An unexpected �5� tilt in the mounting platform at the top of the balloon resulted in large scan-synchronous instrumental signals which were not removable at the level necessary to make an internally consistent measurement of the CMB power spectrum. Minimum-variance maps of the data in all five channels have been made and used to measure the integrated flux from three regions in the Magellanic Clouds, using a flux analysis technique that minimizes the aforementioned instrumental contamination. When combined with data from the COBE/DIRBE instrument, these measurements provide a first look at the integrated emission from extragalactic environments with nearly uniform frequency coverage over the range of 245 to 3000 GHz.
- July 2003
- July 8, 2003
John Everett: Two-phase models of disk-driven outflows in active galactic nuclei with combined hydromagnetic and radiative driving
Scientific Advisor: Arieh Konigl
We present a semianalytic model of steady-state magnetically and radiatively driven disk outflows in Active Galactic Nuclei consisting of a continuous wind with embedded clouds. The continuous outflow is launched from narrow sector on the disk surface as a centrifugally driven wind. Clouds are either uplifted from the disk by the ram pressure of the continuous outflow or are transient, created and destroyed throughout the wind. The inner regions of the outflow shield the outer portions from the strong ionizing central continuum, enabling gas in the outer regions to be radiatively accelerated. This thesis first describes the model in detail, outlines the tests used to verify its accuracy, and then compares it to other outflow models already in use. We present representative solutions of the model to explore the dependence of outflow properties on the relevant physical parameters, and also explore the impact of “ephemeral” (transient) condensations present throughout the wind vs. the disk-launched clouds introduced with the original model. We find agreement with previous models where such comparisons are possible, although we also find that our more detailed radiative acceleration calculations do differ from some previous 2D hydrodynamical simulations. As in previous work, we find that radiative acceleration can have a significant impact on wind kinematics near the surface of the disk. We determine that continuum driving dominates line driving in the wind, whereas line driving accounts for most of the cloud acceleration. Also, when the winds contain dust, radiative acceleration can modify their terminal velocities by 80% over pure centrifugally- driven outflows. Finally, we find that only “ephemeral” clouds can substantially change the structure of the wind for M˙cloud ≲ M˙wind: condensations launched from the accretion disk rapidly accelerate out, of the thin wind and do not significantly affect the geometry or kinematics of the wind.
|Defense Date||Thesis Title||Graduate Student|
|Mapping the Southern Polar Cap with a Balloon-borne Millimeter-wave Telescope||Thomas Crawford|
|Two-phase models of disk-driven outflows in active galactic nuclei with combined hydromagnetic and radiative driving||John Everett|