Computer Science – Sound
Scientific paper
Aug 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.........6m&link_type=abstract
Thesis (PhD). THE JOHNS HOPKINS UNIVERSITY, Source DAI-B 60/02, p. 683, Aug 1999, 172 pages.
Computer Science
Sound
Scientific paper
Observations of carbon monoxide in comets and the circumstellar disk of the star β Pictoris were performed using the Hubble Space Telescope (HST) and a sounding rocket. The Wide Field and Planetary Camera 2 (WFPC2), the Faint Object Spectrograph (FOS) and the Goddard High Resolution Spectrograph (GHRS) were used for imaging and low resolution spectroscopic observations of several solar system comets. The GHRS was used for medium and high resolution spectroscopic studies of the β Pictoris circumstellar disk system. The sounding rocket was use to perform long-slit ultraviolet (UV) spectroscopy of comet Hale-Bopp near perihelion. The first part of this thesis discusses the HST observations. The results of UV spectroscopy with the FOS of comet Hyakutake acquired in June of 1996 will be presented. Emission from both the CO Fourth Positive system (A1Π-X1Σ +) and the CO Cameron system (a3Π-X 1Σ+) are observed in the spectra of this comet. Formation mechanisms for CO in the a3Π state are discussed including electron impact excitation of CO and photodissociation Of CO2. Because these mechanisms produce Cameron emission characterized by different rotational temperatures they are used to derive both CO and CO 2 production rates. WFPC2 imaging and FOS and GHRS spectroscopy were performed on the periodic comet Schwassmann-Wachmann I (SW1) in March of 1996 while this comet was in outburst. From the images a dust outflow velocity of 0.16 km s-1 was derived and the implications of this for the dust size distribution in this comet are discussed. The lack of a detection of CO in the GHRS spectra of SW1 is reconciled with the fact that CO has previously been detected in the coma of this comet in the millimeter wavelength region. Finally, GHRS spectroscopy of the circumstellar disk of β Pictoris is presented. Particular attention is given to the presence of the CO Fourth Positive system and the C I λ1561 absorption features. We determine that the derived CO column density is consistent with evaporation from cometary bodies around the star and that the C column is consistent with its source being photodissociation of the observed CO by the interstellar radiation field. The second part of this thesis discusses the design and calibration of, and the results obtained from NASA-JHU sounding rocket 36.156 UG. The rocket was used to perform long-slit UV spectroscopy of comet Hale-Bopp on 6 April 1997 when the comet was near perihelion. The long slit allows spatial mapping of the emissions in the coma. Particular attention is given to the profiles of the CO Fourth Positive system emissions and C I λλ 1561 and 1657 emissions. It is found that photodissociation of the observed CO can account for the profiles of the observed C. The results and methods of the absolute UV calibration of the sounding rocket payload, including the flat fielding technique used for the spectrograph and detector, are presented. Also discussed is the design and some of the image characteristics of the detector used for this rocket, a double-microchannel-plate with CsI photocathode and a double-delay-line anode.
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