High-angular-resolution astrometry and array phasing with large ground-based telescopes.

Persistent Link:
http://hdl.handle.net/10150/186905
Title:
High-angular-resolution astrometry and array phasing with large ground-based telescopes.
Author:
Dekany, Richard George
Issue Date:
1994
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Extrasolar planets orbiting nearby stars induced small perturbations to the apparent position of the star against a reference. The same perturbations, however, can be induced by the propagation of light through the Earth's turbulent atmosphere. The differential centroid motion between a target star and a reference star of small angular separation, a double star system, has been investigated. We have verified the theory of differential centroid motion in the 2-20 arcsec separation regime as a function of aperture diameter and integration time. We have conducted a comparison of the traditional centroid differencing technique of planet detection and an alternate technique using the cross-correlation of the two short-exposure speckle-grams to form a separation estimate. The speckle cross-correlation technique can exceed the differential centroid technique in precision, but is a strong function of the effective thickness of the turbulent atmosphere. Even so, we have determined that the atmosphere will allow an 8 meter diameter telescope to achieve standard errors sufficient to detect the presence of Jupiter-sized planets in orbit about Sun-sized stars at 10 pc at a 5 sigma confidence with regular observations of 20 minutes in length when r₀ = 20 cm at λ = 0.9 μm. Achieving this precision in practice will require unprecedented control of systematic errors. Also with the motivation of unprecedented angular resolution astrometry, we have developed a new theory and experimentally verified a piston-phasing technique for array telescopes that resulted in a diffraction-limited image from a 6.87 meter baseline imaging array at a wavelength of 2.2 microns, the highest resolution image ever obtained to date of a star from the ground. Finally, we have demonstrated the feasibility and utility of predicting centroid motion over a 6.87 meter baseline imaging array. We have shown how spatial information improves the prediction compared to temporal information alone, particularly in poor seeing conditions. We have verified that for moderate conditions at the MMT site, simple delta rule training of a linear predictor yields excellent results and that the complexity of a two-layer perceptron neural network based predictor is not necessary.
Type:
text; Dissertation-Reproduction (electronic)
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Optical Sciences; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Angel, J. Roger P.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleHigh-angular-resolution astrometry and array phasing with large ground-based telescopes.en_US
dc.creatorDekany, Richard Georgeen_US
dc.contributor.authorDekany, Richard Georgeen_US
dc.date.issued1994en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractExtrasolar planets orbiting nearby stars induced small perturbations to the apparent position of the star against a reference. The same perturbations, however, can be induced by the propagation of light through the Earth's turbulent atmosphere. The differential centroid motion between a target star and a reference star of small angular separation, a double star system, has been investigated. We have verified the theory of differential centroid motion in the 2-20 arcsec separation regime as a function of aperture diameter and integration time. We have conducted a comparison of the traditional centroid differencing technique of planet detection and an alternate technique using the cross-correlation of the two short-exposure speckle-grams to form a separation estimate. The speckle cross-correlation technique can exceed the differential centroid technique in precision, but is a strong function of the effective thickness of the turbulent atmosphere. Even so, we have determined that the atmosphere will allow an 8 meter diameter telescope to achieve standard errors sufficient to detect the presence of Jupiter-sized planets in orbit about Sun-sized stars at 10 pc at a 5 sigma confidence with regular observations of 20 minutes in length when r₀ = 20 cm at λ = 0.9 μm. Achieving this precision in practice will require unprecedented control of systematic errors. Also with the motivation of unprecedented angular resolution astrometry, we have developed a new theory and experimentally verified a piston-phasing technique for array telescopes that resulted in a diffraction-limited image from a 6.87 meter baseline imaging array at a wavelength of 2.2 microns, the highest resolution image ever obtained to date of a star from the ground. Finally, we have demonstrated the feasibility and utility of predicting centroid motion over a 6.87 meter baseline imaging array. We have shown how spatial information improves the prediction compared to temporal information alone, particularly in poor seeing conditions. We have verified that for moderate conditions at the MMT site, simple delta rule training of a linear predictor yields excellent results and that the complexity of a two-layer perceptron neural network based predictor is not necessary.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineOptical Sciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairAngel, J. Roger P.en_US
dc.contributor.committeememberHege, Keithen_US
dc.contributor.committeememberFrieden, B. Royen_US
dc.identifier.proquest9517522en_US
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