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Dissertation/Thesis Abstract

I. The detectability of occultation events for outer solar system objects. II. Measuring temporal symmetry in quasar variation
by Nihei, Taryn Candace, Ph.D., University of Pennsylvania, 2009, 128; 3381767
Abstract (Summary)

This is a two-part dissertation in which I discuss two topics. Each utilizes time-series analysis to quantitatively parameterize observed and simulated astronomical light curves.

In Chapter 2 I present a study of the indirect detection of objects in the outer solar system, from the Kuiper Belt to the Oort Cloud. By parameterization of the width and depth of simulated occultation light curves which account for diffraction effects, background source size, stellar spectra, finite passbands, and finite sampling, I quantify the detectability of occultation events. I then consider the specifications of three telescope systems to determine the sensitivity of these systems to outer solar system occultation events. From this study, I conclude that a modest ground survey sampling at a rate of 5 Hz with signal-to-noise ratio of ∼ 8 is sufficient for the detection of Kuiper Belt objects with radii r [special characters omitted] 1.5 km. In addition, such a survey would be able to detect occultation events by objects in the Oort Cloud. Detection of occultation events by inner Oort Cloud objects with radii r [special characters omitted] 10 km are possible. Larger objects with r [special characters omitted] 100 km will be detectable in the outer Oort Cloud regions. In addition, I show that surveys with higher signal-to-noise ratios and higher sampling rates will be able to probe the lower range of the Kuiper Belt size distribution down to objects with radii r ∼ 0.3 km.

Chapter 3 is an inquiry into the nature of quasar optical variations that explores the feasibility of a microlensing source for quasar variation. The microlensing hypothesis posits that microlensing by compact objects is a significant contributor to quasar optical variation. Microlensing does not exhibit any arrow of time—there is no consistent temporal asymmetry across microlensing events which exhibit either a rapid-rise and slow-decay or a slow-rise and rapid-decay. Therefore, a predicted consequence of a significant microlensing contribution to quasar light curve fluctuations, is the temporal symmetry or lack of an arrow of time in quasar brightness records. In this chapter I will first introduce a quantitative method of measuring the presence or lack of an arrow of time in the brightness records of quasar curves. This method is then applied to a set of 59 quasar light curves from the MACHO database. Evidence for an arrow of time is searched for in each individual curve, and in the ensemble. The results show asymmetry in all of the individual MACHO quasar light curves. However, there is no consistently favored direction for an arrow of time when looking at the entire quasar sample. Therefore, the ensemble exhibits evidence for an underlying symmetric variation in time. The baseline and sampling rate of observations mean that the MACHO database light curves are sensitive to variation timescales that correspond to less than several years. Given the results of this study, we cannot rule out a microlensing contribution from objects with 2 × 10−4 [special characters omitted] M/[special characters omitted] 5 × 10−2.

Indexing (document details)
Advisor: Alcock, Charles
School: University of Pennsylvania
School Location: United States -- Pennsylvania
Source: DAI-B 70/10, Dissertation Abstracts International
Subjects: Astronomy
Keywords: Occultation events, Quasars, Solar system
Publication Number: 3381767
ISBN: 978-1-109-43197-1
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