Physical Sciences and Mathematics Commons^™

Brown Dwarf Atmospheres At High Cadence And Spectral Resolution: A Speed Limit On Brown Dwarf Rotation And A Spectroscopic Atlas Of A 1050 K Atmosphere, Megan E. Tannock

Electronic Thesis and Dissertation Repository

Brown dwarfs are sub-stellar objects that form like stars but are not sufficiently massive to sustain hydrogen fusion in their cores. Characterized by cool, molecule-rich atmospheres, brown dwarfs demonstrate great diversity in spectroscopic appearance and share many properties with giant exoplanets. In this thesis I present two investigations: the first is a detailed photometric and spectroscopic study of the three most rapidly rotating brown dwarfs. The second examines a spectrum of a cool brown dwarf at unprecedented spectral resolution and signal-to-noise ratio to study the accuracy of theoretical model photospheres.

Photometric monitoring of brown dwarfs has revealed that periodic variability …

The Hashtag Project: The First Submillimeter Images Of The Andromeda Galaxy From The Ground, Matthew W.L. Smith, Stephen A. Eales, Thomas G. Williams, Bumhyun Lee, Zongnan Li, Pauline Barmby, Martin Bureau, Scott Chapman, Brian S. Cho, Aeree Chung, Eun Jung Chung, Hui Hsuan Chung, Christopher J.R. Clark, David L. Clements, Timothy A. Davis, Ilse De Looze, David J. Eden, Gayathri Athikkat-Eknath, George P. Ford, Yu Gao, Walter Gear, Haley L. Gomez, Richard De Grijs, Jinhua He, Luis C. Ho, Thomas M. Hughes, Sihan Jiao, Zhiyuan Li, Francisca Kemper

Physics and Astronomy Publications

Observing nearby galaxies with submillimeter telescopes on the ground has two major challenges. First, the brightness is significantly reduced at long submillimeter wavelengths compared to the brightness at the peak of the dust emission. Second, it is necessary to use a high-pass spatial filter to remove atmospheric noise on large angular scales, which has the unwelcome side effect of also removing the galaxy's large-scale structure. We have developed a technique for producing high-resolution submillimeter images of galaxies of large angular size by using the telescope on the ground to determine the small-scale structure (the large Fourier components) and a space …

The X-Rays Wind Connection In Pg 2112+059, C. Saez, W. N. Brandt, F. E. Bauer, G. Chartas, T. Misawa, F. Hamann, Sarah C. Gallagher

Physics and Astronomy Publications

We study the connection between the X-ray and ultraviolet (UV) properties of the broad absorption line (BAL) wind in the highly X-ray variable quasar PG 2112+059 by comparing Chandra-ACIS data with contemporaneous UV HST/STIS spectra in three different epochs. We observe a correlation whereby an increase in the equivalent widths (EWs) of the BALs is accompanied by a redder UV spectrum. The growth in the BAL EWs is also accompanied by a significant dimming in soft X-ray emission (≳2, keV), consistent with increased absorption. Variations in the hard X-ray emission (≳2, keV) are only accompanied by minor spectral variations of …

Revisiting Polycyclic Aromatic Hydrocarbon Emission In Photodissociation Regions, Ameek K. Sidhu

Electronic Thesis and Dissertation Repository

The mid-infrared (IR) spectrum of almost all objects in the Universe is dominated by a set of strong emission features characteristic of a class of large organic molecules made of carbon and hydrogen known as polycyclic aromatic hydrocarbons (PAHs). These molecules account for ~15% of the cosmic carbon and ~20% of the total IR power of the Milky Way and star-forming galaxies. They are strong absorbers of ultraviolet (UV) photons and release the absorbed energy through vibrational transitions that result in strong IR emission features. PAHs play a critical role in the evolution of the interstellar medium (ISM) as they …

Developing A Bytownite Calibration Curve As A Lunar Analogue, Trevor W. Matterson

Undergraduate Student Research Internships Conference

Planetary analogue materials are useful to help interpret and predict planetary processes on other planetary bodies that we cannot observe directly. Lunar analogue materials include terrestrial rocks and minerals with compositions and textures like those on the moon. This project investigates the lunar analogue mineral bytownite to quantify shock effects on the moon using strain related mosaicity determined through micro x-ray diffraction (µXRD). Calibrating strain information as a function of shock pressure for these minerals will enable us to extract peak shock pressures (in GPa) from naturally shocked materials, such as lunar meteorites and Apollo samples, using µXRD

Space Resource Discussions Within The United Nations Committee On The Peaceful Uses Of Outer Space Legal Subcommittee: The Past, Present And Future, Anne Campbell

Institute for Earth and Space Exploration White Papers

The sixtieth session of the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) Legal Subcommittee occurred virtually between May 31^st, 2021 and June 11^th, 2021. The sixtieth session of the Legal Subcommittee included the highly anticipated scheduled informal consultations on “potential legal models for activities in exploration, exploitation and utilization of space resources” (United Nations Office of Outer Space Affairs, 2021f, p.2), which concluded with the establishment of a COPUOS Legal Subcommittee Working Group under a five-year workplan (United Nations Office of Outer Space Affairs, 2021f, p.33). The establishment of a Legal Subcommittee …

Investigation Of Shocked Basalts From Vargeão Dome And Vista Alegre: Implications For The Search For Life On Mars, Nikol Posnov

Electronic Thesis and Dissertation Repository

Impact craters represent excellent astrobiological targets for planetary exploration missions to Mars. The impact of an asteroid or comet into a crystalline, H₂O-bearing target may result in development of a hydrothermal system and increase the habitability of the substrate for the colonization of endolithic microorganisms. Given that Mars’ surface is covered by cratered basaltic rock, this study investigated target rocks and impact breccias from Vargeão Dome and Vista Alegre impact structures that formed in basalt in the Paraná Basin of Brazil.

Utilizing petrography and micro-X-ray diffraction (μXRD), the degree of shock metamorphism in plagioclase was quantitively determined. Measuring …

Mathematical Modelling & Simulation Of Large And Small Scale Structures In Star Formation, Gianfranco Bino

Electronic Thesis and Dissertation Repository

This thesis aims to study the magnetic and evolutionary properties of stellar objects from the prestellar phase up to and including the late protostellar phase. Many of the properties governing star formation are linked to the core’s physical properties and the magnetic field highly dictates much of the core’s stability.

The thesis begins with the implementation of a fully analytic magnetic field model used to study the magnetic properties governing the prestellar core FeSt 1-457. The model is a direct result of Maxwell’s equations and yields a central-to-surface magnetic field ratio in the equatorial plane in cylindrical coordinates. The model …

Fitting An Analytic Magnetic Field To A Prestellar Core, Gianfranco Bino, Shantanu Basu

Physics and Astronomy Publications

We deploy and demonstrate the capabilities of the magnetic field model developed by Ewertowski & Basu by fitting observed polarimetry data of the prestellar core FeSt 1-457. The analytic hourglass magnetic field function derived directly from Maxwell's equations yields a central-to-surface magnetic field strength ratio in the equatorial plane, as well as magnetic field directions with relative magnitudes throughout the core. This fit emerges from a comparison of a single plane of the model with the polarization map that results from the integrated properties of the magnetic field and dust throughout the core. Importantly, our fit is independent of any …

Formation Of Supermassive Black Holes In The Early Universe, Arpan Das

Electronic Thesis and Dissertation Repository

The aim of the work presented in this thesis is to understand the formation and growth of the seeds of the supermassive black holes in early universe. Supermassive black holes (SMBH) with masses larger than 10⁸M_Sun have been observed when the Universe was only 800 Myr old. The formation and accretion history of the seeds of these supermassive black holes are a matter of debate. We consider the scenario of massive seed black hole formation which allows gas to directly collapse into a black hole (DCBH) of similar mass. Considering this scenario, we show that the mass …

Distances To Galactic X-Ray Binaries With Gaia Dr2, R. M. Arnason, H. Papei, P. Barmby, A. Bahramian, M. D. Gorski

Physics and Astronomy Publications

Precise and accurate measurements of distances to Galactic X-ray binaries (XRBs) reduce uncertainties in the determination of XRB physical parameters. We have cross-matched the XRB catalogues of Liu, van Paradijs & van den Heuvel to the results of Gaia Data Release 2. We identify 86 XRBs with a Gaia candidate counterpart, of which 32 are low-mass X-ray binaries (LMXBs) and 54 are high-mass X-ray binaries (HMXBs). Distances to Gaia candidate counterparts are, on average, consistent with those measured by Hipparcos and radio parallaxes. When compared to distances measured by Gaia candidate counterparts, distances measured using Type I X-ray bursts are …

On The Observational Difference Between The Accretion Disk-Corona Connections Among Super- And Sub-Eddington Accreting Active Galactic Nuclei, Hezhen Liu, B. Luo, W. N. Brandt, Michael S. Brotherton, Sarah C. Gallagher, Q. Ni, Ohad Shemmer, J. D. Timlin

Physics and Astronomy Publications

We present a systematic X-ray and multiwavelength study of a sample of 47 active galactic nuclei (AGNs) with reverberation mapping measurements. This sample includes 21 super-Eddington accreting AGNs and 26 sub-Eddington accreting AGNs. Using high-state observations with simultaneous X-ray and UV/optical measurements, we investigate whether super-Eddington accreting AGNs exhibit different accretion disk-corona connections compared to sub-Eddington accreting AGNs. We find tight correlations between the X-ray-to-UV/optical spectral slope parameter (α OX) and the monochromatic luminosity at 2500 Å (L 2500Å) for both the super- and sub-Eddington subsamples. The best-fit α OX-L 2500Å relations are consistent overall, indicating that super-Eddington accreting AGNs …

Gibbs Point Process Model For Young Star Clusters In M33, Dayi Li, Pauline Barmby

Physics and Astronomy Publications

We demonstrate the power of Gibbs point process models from the spatial statistics literature when applied to studies of resolved galaxies. We conduct a rigorous analysis of the spatial distributions of objects in the star formation complexes of M33, including giant molecular clouds (GMCs) and young stellar cluster candidates (YSCCs). We choose a hierarchical model structure from GMCs to YSCCs based on the natural formation hierarchy between them. This approach circumvents the limitations of the empirical two-point correlation function analysis by naturally accounting for the inhomogeneity present in the distribution of YSCCs. We also investigate the effects of GMCs' properties …

Spectral Properties Of Lunar Impact Melt Deposits From Moon Mineralogy Mapper (M3) Data, Catherine Neish, Kevin Cannon, Livio Tornabene, Roberta Flemming, Michael Zanetti, Eric Pilles

Earth Sciences Publications

Lunar impact melt deposits have unusual surface properties, unlike any measured terrestrial lava flow. Radar observations suggest that they are incredibly rough at decimeter scales, but they appear smooth in high-resolution, meter-scale optical images. The cause of their unusual surface roughness is unknown. In this work, we investigate the properties of impact melt deposits from seven lunar craters, ranging in size from 7.5 to 96 km in diameter, in an effort to understand the cause of their unique surface texture. We use data from the Lunar Reconnaissance Orbiter’s (LRO) Mini-RF instrument to characterize the small-scale roughness of the deposits, data …

Fourier Transform Of The Continuous Gravitational Wave Signal, Sree Ram Valluri, V. Dergachev, X. Zhang, Farrukh Chishtie

Physics and Astronomy Publications

The direct detection of continuous gravitational waves from pulsars is a much anticipated discovery in the emerging field of multimessenger gravitational wave (GW) astronomy. Because putative pulsar signals are exceedingly weak large amounts of data need to be integrated to achieve desired sensitivity. Contemporary searches use ingenious ad hoc methods to reduce computational complexity. In this paper we provide analytical expressions for the Fourier transform of realistic pulsar signals. This provides description of the manifold of pulsar signals in the Fourier domain, used by many search methods. We analyze the shape of the Fourier transform and provide explicit formulas for …