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<p> The heliosphere is a &ldquo;comet-like&rdquo; bubble of plasma reaching from &sim;10² to over 10³ astronomical units in size. It is created by the outflow of solar wind (SW) plasma and its interaction with the partially-ionized local interstellar medium (LISM). Due to its large size, it is unfeasible to take <i>in situ</i> measurements at the edges of this interaction. Therefore it is necessary to develop sensing techniques to remotely probe the heliosphere and its boundaries. </p><p> The NASA-funded <i>Interstellar Boundary EXplorer</i> (<i>IBEX</i>) mission is aimed at improving our understanding of the heliospheric interface. Launched in 2008 October, <i>IBEX</i> measures fluxes of energetic neutral atoms (ENAs) that are created through the SW&ndash;LISM interaction, as well as interstellar neutral atoms that permeate the heliospheric boundary. Out of the neutral atom species that <i> IBEX</i> can detect, hydrogen (H) atoms are the most abundant in interstellar space and the heliosphere. Hydrogen ENAs, in particular, are created when relatively energetic protons from the heliospheric plasma charge-exchange with interstellar H atoms. Due to their high energies, and thus large mean free paths, H ENAs can propagate large distances before ionizing (i.e., on the order of the size of the heliosphere), and can be detected by <i> IBEX.</i> </p><p> The purpose of this study is to simulate H ENA flux measurements at 1 AU and relate these to the <i>IBEX</i> mission. Three goals of this study that are of particular interest to <i>IBEX</i> are: (1) to simulate H ENA fluxes measured in the solar (inertial) and <i>IBEX</i> spacecraft frames of reference in order to better understand <i>IBEX </i> measurements made in different frames of reference; (2) to study the effects of pickup ions, i.e., non-thermalized ions, on H ENA fluxes, and determine how <i>IBEX</i> observations can reveal the properties of PUIs in the distant heliosphere; (3) to analyze the effects of a time-dependent solar cycle on <i>IBEX</i> H ENA measurements, particularly the &ldquo;ribbon&rdquo; of enhanced flux encircling the sky. The simulations are performed by post-processing a pre-simulated, &ldquo;background&rdquo; heliosphere containing plasma and neutral H properties (e.g., density, temperature, velocity) produced from a three-dimensional magnetohydrodynamic/kinetic simulation of the SW&ndash;LISM interaction.</p>

<p>If a distant star happens to host an orbiting exoplanet, then that planet will exert a gravitational influence on the star that may be detectable from the earth by the apparent ``stellar wobble''---regular, periodic variations in the observed radial velocities. Two complicating factors, however are ``stellar jitter'' and measurement errors, both of which generate radial velocity ``noise''. As a result, it is not always obvious whether variations in radial velocities are due to an orbiting planet or to mere noise. The problem of model selection---is that a planet or not?---may be addressed by using any number of summary statistics, and the choice may be made using frequentist hypothesis testing, Bayesian model selection, or likelihood analysis.</p><p>Here we compare the planet-detecting ability of three different statistics: the ``Maximal Periodogram Spike'', or the height of the tallest spike in the Lomb-Scargle periodogram; the Maximum Likelihood Ratio; and the Bayes Factor. We measure the usefulness of each statistic by how many observations would be required before the statistic would able to distinguish accurately the no-planet model from the one-planet model when presented with data from a star hosting a planet of one of six different types---we vary the magnitude of the radial velocity function's semi-amplitude and the eccentricity of the orbit. The data are simulated, using observations made at random times.</p><p>We find that the current practice of examining the tallest spike in the periodogram cannot easily be improved upon using either the Maximum Likelihood Ratio (which performs comparably) or the Bayes Factor (which is exceedingly difficult to estimate for eccentric orbits unless it is already plain that a planet is present). We also conclude that a planet having a semiamplitude of 3 m/s (which could potentially correspond to the smallest planet yet discovered outside of a multi-planet system) could in fact be detected using current methods, if there was an initial commitment to make at least 150 or 200 radial velocity observations on the same candidate star, even in the absence of growing evidence for planetary presence.</p> / Dissertation

Nulling stellar interferometry may enable the discovery of earth-like planets around other stars. In nulling mode, the zero order fringe is destructive and on axis, thus canceling light from a bright source and detecting dimer off-axis features. To create deep on-axis nulls, the phase must be shifted half a wave achromatically over a broad band. The phase shift is created by adding optical path thickness with dielectric plates. Plates of different materials can balance dispersion. The nulling solutions found for TPF (infrared) and for SIM (visible) are promising. This dissertation describes the implementation of a nulling beam combiner test bed and presents data characterizing its performance. Although the implementation was limited so that a broad band null of 10E-4 was not attained, the test bed revealed the extreme challenges of this technique and provided very valuable lessons that will enable future implementations to be successful and more precise. The nulling beam combiner testbed was implemented in the laboratory as a Michelson interferometer with the goal of achieving a stabilized, l0E-4 null over a spectral region from 600 nm to 800 nm. The beam combiner system has three tiers of control. Tier 1 controls phase achromaticity by tilting optical plates and is a static control loop. Tier 2 sweeps through the white light fringe and then searches for the null as the air path drifts over minutes. Tier 3 stabilizes the null with a 300 hertz servo loop. A scheme for active control of the optical thicknesses was developed. The phase as a function of wavelength was measured by performing PSI on a spectrally dispersed fringe. The phase was fit to a model to solve for the optical thicknesses. The optical thicknesses were then adjusted to match the ideal thicknesses of an optimized solution. This process of measuring and adjusting the optical thicknesses is performed iteratively to achromatize the phase. The stabilizing servo loop sensed on a grey fringe at a short wavelength. At the shorter wavelength, the fringe was 90 degrees out of phase with the main pass band resulting in a grey fringe. The grey fringe intensity is more sensitive to OPD changes.

An achromatic shearing phase sensor is proposed as a phasing technique for the alignment of segmented telescopes. The sensor is based upon a shearing interferometer using two-wavelength interferometry methods. The two beams are created with a diffraction grating. The diffracted orders are re-imaged such that the pupil plane is focused onto a CCD array with a shear displacing the two orders. The amount of shear is equal to the size of the re-imaged segments. The sensor was measured to have a capture range of at least 5 μm, and an accuracy of 0.3 μm or better. The repeatability was 0.1 vm. The sensor is very sensitive to field dependent aberrations in its optical design but the resulting errors can be calibrated. The sensor is an improvement over similar technologies because it can measure and compensate for segment aberrations with tilt and piston adjustments. The sensor is compatible with many mature interferometry techniques and can be used with extended and broadband sources.

This dissertation describes the development, calibration, and testing of the adaptive optics system for the 6.5 m Multiple Mirror Telescope. By employing a deformable secondary mirror, the MMT adaptive optics system uniquely solves several problems typical of astronomical adaptive optics systems. Extra components are eliminated, improving throughput and reducing emissivity. Since the adaptive secondary is integral to the telescope, a corrected beam is presented to any instrument mounted at Cassegrain focus. The testing of an adaptive mirror, which is large and convex, poses a new and difficult problem. I present a test apparatus that allows complete calibration and operation, in closed-loop, of the entire adaptive optics system in the laboratory. The test apparatus replicates the optical path of the telescope with a wavefront error of less than 500 nm RMS. To simulate atmospheric turbulence, machined acrylic plates are included. A phase-shifting interferometer allows calibration of the Shack-Hartmann wavefront sensor and reconstruction algorithms; comparisons agree to one-third of the root-mean-square wavefront. First, techniques were developed to align the apparatus and measure residual aberration. Then, the wavefront sensor was calibrated by measuring its response to introduced tilt. Lastly, a Fourier wave-optics approach was used to produce a modal wavefront reconstructor. The adaptive secondary mirror uses electro-magnetic force actuators. Capacitive position sensors are placed at each actuator to permit control of the mirror shape without measuring the reflected wavefront. These sensors have nanometer resolution, but require calibration. To calibrate the sensors, I developed a small optical instrument which measures the thickness of transparent films to an absolute accuracy of 5 nm with a precision of 2 nm. The device has applications far beyond the scope of this research. Twenty-four of these optical gap sensors have been built to calibrate the 336 capacitive sensors on the adaptive secondary mirror. Mirror displacements measured using gap sensors and a phase-shifting interferometer agree to 2 percent of the displacement. The gap sensors allow for quick and accurate calibration of the capacitive sensors without the difficulty of installing an interferometer on the telescope.

Fundamental observations of molecular hydrogen (H₂) in dark clouds, star forming regions, and radiation-dominated environments are presented, modeled, and interpreted. Through a weak infrared absorption line spectrum, the abundance of cold H₂ in dark molecular clouds and star forming regions is measured directly and compared with the abundance of its most commonly cited surrogate, CO. The derived abundance of CO is between 1.5 and 2.5 x 10⁻⁴ for the sample. The CO molecule thus represents about ⅓ of the total carbon budget in dense clouds. Also detected via infrared line absorption is the pivotal molecular ion H⁺₃ , yielding a direct measure of the cosmic ray ionization rate of H₂ in dark molecular clouds (between 1 and 5 x 10⁻¹⁷ s⁻¹), a process that instigates the complex ion-neutral chemical pathways that form many of the 120+ known molecular species deep inside interstellar clouds. These timely tests of theory are applied to the detailed submillimeter-wave study of the ρ Ophiuchi star forming cloud and photodissociation front, allowing partial disentanglement of the complicated physical and chemical structure of a star forming cloud. Yet H₂ and H⁺₃ continue to surprise and delight us with more mysteries. The formation, excitation and survival of molecules in unusual & hostile environments is highlighted by the discoveries of H⁺₃ in circumstellar disks of early-type stars, and of fluorescing H₂ in two harshly-irradiated filaments of the Crab Nebula. The role of H⁺₃ as a possible tracer of planet formation, and the evolution of H₂ in the interstellar medium is discussed. The study of H₂ in hostile environments is extended to the ensemble properties of extragalactic star forming regions, and applied to the Arp 299 merger system as a unique probe of the feedback of newly-formed hot stars, their fossil remains, and the molecular material which formed them.