Evolved stars including asymptotic giant branch stars, proto-planetary nebulae and planetary nebulae are well known to be sources of molecules for the interstellar medium. Circumstellar envelopes of asymptotic giant branch stars are known to be sites of active molecular synthesis. These molecular species are then distributed to the interstellar medium as the envelope is gradually ejected in the proto-planetary nebula and planetary nebula phases. As carbon that is dredged-up from the stellar core by convectional instabilities facilitates rapid formation and reprocessing of molecules, the chemical abundances differ significantly between objects at different stages of stellar evolution. Changes in the physical conditions in the envelope also allow different chemical processes to take place throughout the evolutionary sequence. Conducting spectral line surveys on a large sample of objects at different stages of stellar evolution will allow one to track those chemical and physical changes along the evolutionary track. Presented in this thesis are the results from a series of unbiased systematic line surveys targeting the circumstellar envelopes of evolved stars. As part of an on-going effort, these surveys aim to expand the coverage both in terms of objects at different evolutionary stages and wavelength ranges in order to paint a more complete picture in our understanding of the chemical evolution in objects at the final stages of stellar evolution. All surveys included in the present study are conducted using the 45m radio telescope at the Nobeyama Radio Observatory, and the same instrumental settings were used when observing a given frequency region to minimize the systematic uncertainties. The four objects surveyed in this study, the asymptotic giant branch star CIT6, the proto-planetary nebulae CRL 2688 and CRL 618, and the planetary nebula NGC7027, represent a healthy sample from all key phases of late-stage stellar evolution. Since the surveys are conducted in millimeter-wavelengths, they are mostly targeting rotational transitions from molecules. In particular, rotational transitions associated with the cyanopolyyne chain HC7N reported in the survey of CIT6 and CRL 2688 are novel detections. Spectra from the series of surveys are analyzed using previously obtained spectra of the prototypical asymptotic giant branch star IRC+10216 as a benchmark. Results from fractional abundance computations suggested that CIT6 is a more evolved specimen relative to IRC+10216 and supported chemical models pertaining to the synthesis of cyanopolyyne chains. Intensity ratios in CRL 2688 showed that the cyanopolyyne enrichment towards conclusion of the asymptotic giant branch phase is no longer present in proto-planetary nebulae. Rotational analysis provided evidence to support the hypothesis that the ammonia absorption in CRL 618 originates from two distinct components. Flux ratios in NGC7027 also showed that the recombination lines in the planetary nebula behave according to theoretical predictions. Altogether, these findings will complement previous results and enable one to trace and understand the interplay between chemistry and physical conditions within the circumstellar envelope as objects proceeds on the evolutionary track. / published_or_final_version / Physics / Master / Master of Philosophy

No description available.

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Thesis (Ph. D.)--University of Massachusetts Amherst, 2009. / Open access. Includes bibliographical references (p. 179-184). Print copy also available.

Thesis (Ph. D.)--University of Cambridge, 1998. / Includes bibliographical references (p. 197-201).

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics, Jun. 2003. / Includes bibliographical references (p. 168-171). Also available on the Internet.

The performance of existing and planned millimeter and submillimeter astronomical arrays is limited by fluctuations in the amount of atmosperic water vapor along the atenna's line of sight. Correcting the resulting phase distortion of the received signals is seen as a significant technological challenge. Measurements of the variation in the line-of-sight water vapor abundance at the level of 1 micron precipitable water vapor on a time scale of 1 second and at arbitrary antenna positions are required. This thesis describes the design of, and preliminary results obtained with, a water vapor monior operating at abundance at the level 1 micron precipitable water vapor on a time scale of 1 second and at arbitrary antenna positions are required. This thesis describes the design of, and preliminary results obtained with, a water vapor monitor operating at infrared wavelengths which shows considerable promise for this application. Improvements in, and future plans for, the second generation water vapor monitor currently under development are also discussed. / xiii, 167 leaves : ill. ; 28 cm.

abstract: TolTEC is a three-color millimeter wavelength camera currently being developed for the Large Millimeter Telescope (LMT) in Mexico. Synthesizing data from previous astronomy cameras as well as knowledge of atmospheric physics, I have developed a simulation of the data collection of TolTEC on the LMT. The simulation was built off smaller sub-projects that informed the development with an understanding of the detector array, the time streams for astronomical mapping, and the science behind Lumped Element Kinetic Inductance Detectors (LEKIDs). Additionally, key aspects of software development processes were integrated into the scientific development process to streamline collaboration across multiple universities and plan for integration on the servers at LMT. The work I have done benefits the data reduction pipeline team by enabling them to efficiently develop their software and test it on simulated data. / Dissertation/Thesis / Masters Thesis Software Engineering 2019

The IRMA III infrared radiometer is a passive atmospheric water vapor detector designed for use with interferometric submillimeter arrays as a method of phase correction. The IRMA III instrument employs a distributed, multi-tasking software control system permitting precise fine-grained control at remote locations over a low-bandwidth network connection. IRMA's software is divided among three processors tasked with performing three primary functions: command interpretation, data collection and motor control of IRMA's Alt-Az mount. IRMA's hardware control and communication functionality is based on compact, low cost, energy efficient Rabbit 2000 microcontroller modules, selected to meet IRMA's limited space and power requirements. IRMA accepts scripts defined in a custom, high level control language as its method of control, which the operator can write or dynamically generated by a separate GUI front-end program. / xi, 193 leaves : ill. ; 28 cm.

Our group has developed a 20 μm passive atmospheric water vapour monitor. The Infrared Radiometer for Millimetre Astronomy (IRMA) has been commissioned and deployed for site testing for the Thirty Meter Telescope (TMT) and the Giant Magellan Telescope (GMT). Measuring precipitable water vapour (PWV) requires both a sophisticated atmospheric model (BTRAM) and an instrument (IRMA). Atmospheric models depend on atmospheric profiles. Most profiles are generic in nature, representing only a latitude in some cases. Site-specific atmospheric profiles are required to accurately simulate the atmosphere above any location on Earth. These profiles can be created from publicly available archives of radiosonde data, that offer nearly global coverage. Having created a site-specific profile and model, it is necessary to determine the PWV sensitivity to the input parameter uncertainties used in the model. The instrument must also be properly calibrated. In this thesis, I describe the radiometric calibration of the IRMA instrument, and the creation and analysis of site-specific atmospheric models for use with the IRMA instrument in its capacity as an atmospheric water vapour monitor for site testing. / xii, 135 leaves : ill. ; 28 cm. --