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Description
Most stars in our galaxy are M–dwarfs, much cooler and smaller than the sun. The ubiquitous nature of these stars is also paired with the formation of terrestrial exoplanets orbiting them. The strategic placement of M-dwarfs between main-sequence stars and brown dwarfs, their uniqueness as exoplanet analogs, and their dominating presence in the galactic stellar population make them priority targets for study. This work investigates outstanding questions, including the need to acquire constraints on their chemical compositions to decode formation processes, evolution, and interaction with companion objects. Chapter 1 lays out a broad background emphasizing the importance of studying the most populous star in the galaxy, their far-reaching implications, and primarily the numerous challenges in characterizing the atmospheres and environments of these stars. Chapter 2 investigates the influence of M-dwarf star spots propagating into spectra of transiting terrestrial planets, showing that inaccurate modeling of M-dwarf photospheres leads to significant bias when inferring atmospheric properties of companion exoplanets. These biases persist despite correcting M-dwarf spot signatures imprinted onto the exoplanetary spectra, even with high-fidelity JWST observations. This result emphasizes the need for improved stellar atmosphere models as the first step to improving our understanding of the companion planets. To address this, chapter 3 introduces SPHINX—a new stellar atmosphere model grid for M-dwarfs. SPHINX provides improved constraints on fundamental properties of benchmark M-dwarf systems (e.g., temperature, surface gravity, radius, and chemistry). The improvement is significant relative to the state-of-the-art stellar model grid available today. Chapter 4 expands this model, applying it to mid-to-late type M-dwarfs, and investigating chemical trends in their atmospheric properties. Using low-resolution observations, both archival data (from SpeX Prism Library Database) and from previous empirical studies; this chapter presents constraints on fundamental atmospheric properties of 71 low-mass, late-type M-dwarfs to understand spectroscopic degeneracies arising due to stellar activity, cloud/dust condensation and convection. With SPHINX models, the chemical properties of these stars are compared against main-sequence stars to acquire a more holistic understanding of M-dwarfs as a class—in the quest to ultimately characterize their companions.
ContributorsIyer, Aishwarya (Author) / Line, Michael (Thesis advisor) / Patience, Jennifer (Committee member) / Young, Patrick (Committee member) / Shkolnik, Evgenya (Committee member) / O'Rourke, Joseph (Committee member) / Arizona State University (Publisher)
Created2023
Description
TolTEC is a three-band millimeter-wave, imaging polarimeter installed on the 50 m diameter Large Millimeter Telescope (LMT) in Mexico. This camera simultaneously images the focal plane at three wavebands centered at 1.1 mm (270 GHz), 1.4 mm (214 GHz), and 2.0 mm (150 GHz). TolTEC combines polarization-sensitive kinetic inductance detectors (KIDs) with the LMT to produce high resolution images of the sky in both total intensity and polarization. I present an overview of the TolTEC camera’s optical system and my contributions to the optomechanical design and characterization of the instrument. As part of my work with TolTEC, I designed the mounting structures for the cold optics within the cryostat accounting for thermal contraction to ensure the silicon lenses do not fracture when cooled. I also designed the large warm optics that re-image the light from the telescope, requiring me to perform static and vibration analyses to ensure the mounts correctly supported the mirrors. I discuss the various methods used to align the optics and the cryostat in the telescope. I discuss the Zemax optical model of TolTEC and compare it with measurements of the instrument to help with characterization. Finally, I present the results of stacking galaxies on data from the Atacama Cosmology Telescope (ACT) to measure the Sunyaev-Zel’dovich (SZ) effect and estimate the thermal energy in the gas around high red-shift, quiescent galaxies as an example of science that could be done with TolTEC data. Since the camera combines high angular resolution with images at three wavelengths near distinct SZ features, TolTEC will provide precise measurements to learn more about these types of galaxies.
ContributorsLunde, Emily Louise (Author) / Mauskopf, Philip (Thesis advisor) / Groppi, Christopher (Committee member) / Scannapieco, Evan (Committee member) / Noble, Allison (Committee member) / Bryan, Sean (Committee member) / Arizona State University (Publisher)
Created2023
Description
Building on the legacies of Planck and the Atacama Cosmology Telescope, among others, future cosmic microwave background (CMB) observatories are poised to revolutionize our understanding of the cosmos by implementing proven detector systems at scales previously incomprehensible. Leading the charge is Simons Observatory (SO), a suite of four telescopes located at 5,200 meters elevation in the Atacama Desert of Chile. With more than 60,000 transition-edge sensor (TES) detectors deployed in six frequency bands across three half-meter telescopes and one 6-meter telescope, SO will observe CMB temperature and polarization at small and large scales with greater sensitivity and control over systematics than has yet been achieved. In deploying more detectors than all other previous CMB experiments combined, SO must also chart new territory in the realm of TES readout. Breakthroughs in microwave multiplexing (μ-mux) readout technology now allow the simultaneous readout of approximately 1,000 detectors on a single set of cables, far surpassing the capabilities of previous systems. For the Large Aperture Telescope’s >30,000 detectors, this translates to a total of just 45 input/output lines. A crucial piece of the SO readout architecture is the Universal Readout Harness (URH), a "plug-and-play" assembly that contains the 300K-4K elements. Configurable to support the readout requirements of each receiver, each URH can support up to 24 readout lines. In addition to the radiofrequency (RF) components, the URH can also support up to 12x50-wire DC cable looms, which provide detector and amplifier power. This dissertation describes the construction and testing of the 6 URHs required for nominal SO operations, as well as the on-site integration of the first Small Aperture Telescope. Separately, an optical stacking analysis of quiescent galaxies at z~1 using images from the Dark Energy Survey is presented. Motivated by a desire to better understand the evolution of massive elliptical galaxies, high signal-to-noise images generated from averaging ~100,000 individual galaxy cutouts are used to calculate surface brightness profiles in the grizY bands. Additionally, the extragalactic background light is derived from these stacks and is found to be in good agreement with previous measurements.
ContributorsMoore, Jenna Elizabeth (Author) / Mauskopf, Philip D (Thesis advisor) / Groppi, Christopher (Committee member) / Scannapieco, Evan (Committee member) / Cohen, Seth (Committee member) / Arnold, Kam (Committee member) / Arizona State University (Publisher)
Created2023
Description
Brown dwarfs are a unique class of object which span the range between the lowest mass stars, and highest mass planets. New insights into the physics and chemistry of brown dwarfs comes from the comparison between spectroscopic observations, and theoretical atmospheric models. In this thesis, I present a uniform atmospheric retrieval analysis of the coolest Y, and late-T spectral type brown dwarfs using the CaltecH Inverse ModEling and Retrieval Algorithms (CHIMERA). In doing so, I develop a foundational dataset of retrieved atmospheric parameters including: molecular abundances, thermal structures, evolutionary parameters, and cloud properties for 61 different brown dwarfs. Comparisons to other modeling techniques and theoretical expectations from the James Webb Space Telescope (JWST) are made. Finally, I describe the techniques used to improve CHIMERA to run on Graphical Processing Units (GPUs), which directly enabled the creation of this large dataset.
ContributorsZalesky, Joseph (Author) / Line, Michael R (Thesis advisor) / Patience, Jennifer (Committee member) / Groppi, Christopher (Committee member) / Young, Patrick (Committee member) / Bose, Maitrayee (Committee member) / Arizona State University (Publisher)
Created2022
Description
The balance between relative numbers, lifetime, and habitable zone (HZ) size of K stars (0.6 – 0.9 M⊙) in comparison with M (0.08 – 0.6 M⊙) and G (0.9 – 1.1 M⊙) stars makes them candidates to host “super-habitable” planets. Understanding the high- energy radiation environment of planets around these stars is crucial, since ultraviolet (UV) and X-ray radiation may cause severe photodissociation and ionization of the atmosphere, with the potential for complete erosion. In this thesis, I present the first broad study of the UV and X-ray evolution of K stars. I first focused on Galaxy Evolution Explorer (GALEX) and Ro ̈ntgen Satellit (ROSAT) photometric UV and X-ray evolutions of K stars and compared this with the age evolution of both early- (0.35 – 0.6 M⊙) and late-M (0.08 – 0.35 M⊙) stars. I found that the fractional UV and X-ray flux from M and K stars is similar; however, the wider and farther HZs of K stars mean that there is less incident UV radiation on HZ planets. Next, I led a spectroscopic study of 41 K stars using Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) data to show that the UV line and continua emission show no decrease in flux beyond 650 Myr whereas early-M star flux declines by 150 Myr; therefore, the K star intrinsic UV flux is greater than early-M stars after this time. I suggest that this phenomenon is related to K star rotational spin-down stalling. Lastly, I revisited the GALEX and ROSAT data with newly-available distances from the Gaia mission for both K and M stars. I find that the UV flux for K stars is an order of magnitude higher for M stars at all ages and the flux in their respective HZs is similar. However, K star X-ray flux is an order of magnitude less in the HZ than for M stars. The age of decline shows a dependency on wavelength, a phenomenon which is not seen in either the early- or late-M star data. These results suggest thatK stars may not exhibit quite the advantage as HZ planet host stars as the scientific community originally thought.
ContributorsRichey-Yowell, Tyler (Author) / Shkolnik, Evgenya (Thesis advisor) / Patience, Jennifer (Committee member) / Jacobs, Daniel (Committee member) / Bowman, Judd (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2022
Description
As a demonstration study of low-resolution spectrophotometry, the photometric redshift estimation with narrow-band optical photometry of nine galaxy clusters is presented in this thesis. A complete data reduction process of the photometryusing up to 16 10nm wide narrow-band optical filters from 490nm − 660nm are provided. Narrow-band photometry data are combined with broad-band photometry (SDSS/Pan-STARRS) for photometric redshift fitting. With available spectroscopic
redshift data from eight of the fields, I evaluated the fitted photometric redshift results and showed that combining broad-band photometric data with narrow-band data result in improvements of factor 2-3, compared to redshift estimations from
broad-band photometry alone. With 15 or 16 narrow-band data combined with SDSS (Sloan Digital Sky Survey) or Pan-STARRS1 (The Panoramic Survey Telescope and Rapid Response System) data, a Normalized Median Absolute Deviation of σNMAD ∼ 0.01−0.016 can be achieved.
The multiband images of galaxy cluster ABELL 611 have been used to further study intracluster light around its brightest cluster galaxy (BCG). It can be shown here that fitting of BCG+ICL stellar properties using the averaged 1-dimensional
radial profile is possible up to ∼ 100kpc within this cluster. The decreasing in age of the stellar population as a function of radius from the BCG+ICL profile, though not entirely conclusive, demonstrates possible future application of low-resolution
spectrophotometry on the ICL studies.
Finally, Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) mission planning study are covered, and a methodology of visualization tool for target availability is described.
ContributorsWang, Pao-Yu (Author) / Mauskopf, Philip (Thesis advisor) / Butler, Nathaniel (Committee member) / Jansen, Rolf (Committee member) / Vachaspati, Tanmay (Committee member) / Arizona State University (Publisher)
Created2022
Description
The Balloon-borne Large Aperture Submillimeter Telescope - The Next Generation (BLAST-TNG) was designed to map the polarized emission from dust in star forming regions of our galaxy. The dust is thought to trace magnetic fields and thus inform us of the role that it plays in star formation. BLAST-TNG improves upon the previous generation of balloon-borne sub-mm polarimeters by increasing the number of detectors by over an order of magnitude. A novel detector technology which is naturally multiplexed, Kinetic Inductance Detectors have been developed as an elegant solution to the challenge of packing cryogenic focal plane arrays with detectors. To readout the multiplexed arrays, custom firmware and control software was developed for the ROACH2 FPGA based system. On January 6th 2020 the telescope was launched on a high-altitude balloon from Antarctica and flew for approximately 15 hours in the mid-stratosphere. During this time various calibration tasks occurred such as atmospheric skydips, the mapping of a sub-mm source, and the flashing of an internal calibration lamp. A mechanical failure shortened the flight so that only calibration scans were performed. In this dissertation I will present my analysis of the in-flight calibration data leading to measures of the overall telescope sensitivity and detector performance. The results of which prove kinetic inductance detectors as a viable candidate for future space based sub-mm telescopes. In parallel the fields of digital communications and radar signal processing have spawned the development of the Radio Frequency System On a Chip (RFSoC). This product by Xilinx incorporates a fabric of reconfigurable logic, ARM microprocessors, and high speed digitizers all into one chip. The system specs provide an improvement in every category of size, weight, power, and bandwidth.This is naturally the desired platform for the next generation of far-infrared telescopes which are pushing the limits of detector counts. I present the development of one of the first frequency multiplexed detector readouts on the RFSoC platform. Alternative firmware designs implemented on the RFSoC are also discussed. The firmware work presented will be used in part or in full for multiple current and upcoming far-infrared telescopes.
ContributorsSinclair, Adrian Kai (Author) / Mauskopf, Philip D (Thesis advisor) / Borthakur, Sanchayeeta (Committee member) / Groppi, Christopher (Committee member) / Jacobs, Daniel (Committee member) / Hubmayr, Johannes (Committee member) / Arizona State University (Publisher)
Created2021
Description
The interactions that take place in the ionized halo of gas surrounding galaxies, known as the circumgalactic medium (CGM), dictates the host galaxy's evolution throughout cosmic time. These interactions are powered by inflows and outflows that enable the transfer of matter and energy, and are driven by feedback processes such as accretion, galactic winds, star formation and active galactic nuclei. Such feedback and the interactions that ensue leads to the formation of non-equilibrium chemistry in the CGM. This non-equilibrium chemistry is implied by observations that reveal the highly non-uniform distribution of lower ionization state species, such as Mg II and Si II, along with widespread higher ionization state material, such as O VI, that is difficult to match with equilibrium models. Given these observations, the CGM must be viewed as a dynamic, multiphase medium, such as occurs in the presence of turbulence. To better understand this ionized halo, I used the non-equilibrium chemistry package, MAIHEM, to perform hydrodynamic (HD) simulations. I carried out a suite of HD simulations with varying levels of artificially driven, homogeneous turbulence to learn how this influences the non-equilibrium chemistry that develops under certain conditions present in the CGM. I found that a level of turbulence consistent with velocities implied by observations replicated many observed features within the CGM, such as low and high ionization state material existing simultaneously. At higher levels of turbulence, however, simulations lead to a thermal runaway effect. To address this issue, and conduct more realistic simulations of this environment, I modeled a stratified medium in a Milky Way mass Navarro-Frenk-White (NFW) gravitational potential with turbulence that decreased radially. In this setup and with similar levels of turbulence, I alleviated the amount of thermal runaway that occurs, while also matching observed ionization states. I then performed magneto-hydrodynamic (MHD) simulations with the same model setup that additionally included rotation in the inner halo. Magnetic fields facilitate the development of an overall hotter CGM that forms dense structures within where magnetic pressure dominates. Ion ratios in these regions resemble detections and limits gathered from recent observations. Furthermore, magnetic fields allow for the diffusion of angular momentum throughout the extended disk and gas cooling onto the disk, allowing for the maintenance of the disk at late times.
ContributorsBuie II, Edward (Author) / Scannapieco, Evan (Thesis advisor) / Borthakur, Sanchyeeta (Committee member) / Groppi, Christopher (Committee member) / Jacobs, Danny (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2022
Description
This dissertation presents a comprehensive study on the advancement of astrophysical radio, microwave, and terahertz instrumentation/simulations with three pivotal components.First, theoretical simulations of high metallicity galaxies are conducted using the supercomputing resources of Purdue University and NASA. These simulations model the evolution
of a gaseous cloud akin to a nascent galaxy, incorporating variables such as kinetic energy,
mass, radiation fields, magnetic fields, and turbulence. The objective is to scrutinize the
spatial distribution of various isotopic elements in galaxies with unusually high metallicities and measure the effects of magnetic fields on their structural distribution.
Next, I proceed with an investigation of the technology used for reading out Microwave Kinetic Inductance Detectors (MKIDs) and their dynamic range limitations tied to the current
method of FPGA-based readout firmware. In response, I introduce an innovative algorithm
that employs PID controllers and phase-locked loops for tracking the natural frequencies
of resonator pixels, thereby eliminating the need for costly mid-observation frequency recalibrations which currently hinder the widespread use of MKID arrays.
Finally, I unveil the novel Spectroscopic Lock-in Firmware (SpLiF) algorithm designed to
address the pernicious low-frequency noise plaguing emergent quantum-limited detection
technologies. The SpLiF algorithm harmonizes the mathematical principles of lock-in amplification with the capabilities of a Fast Fourier Transform to protect spectral information
from pink noise and other low-frequency noise contributors inherent to most detection systems. The efficacy of the SpLiF algorithm is substantiated through rigorous mathematical
formulation, software simulations, firmware simulations, and benchtop lab results.
ContributorsHoh, Jonathan (Author) / Groppi, Christopher E (Thesis advisor) / Jamison-Hooks, Tracee (Committee member) / Buie II, Edward (Committee member) / Trichopoulos, Georgios (Committee member) / Scannapieco, Evan (Committee member) / Arizona State University (Publisher)
Created2024
Description
In this opus, I challenge the claim that inflationary spacetimes must be past geodesi-cally incomplete. To do this, I utilize the warped product formalism of Bishop and
O’Neill and build upon the venerable Friedmann Robertson Walker (FRW) space-
time formalism to the Generalized Friedmann Robertson Walker (GFRW) spacetime
formalism, where the achronal spacelike sections can be any geodesically complete
Riemannian manifold (Σ, gΣ ). I then solve the GFRW geodesic equation in generality
as a functional of the scale factor f , and derive a main theorem, which characterizes
the geodesic completeness in GFRW spacetimes. After offering a definition of infla-
tion which enumerates the topological requirements which permit a local foliation of
a scale factor, I discuss a cohort of geodesically complete inflationary GFRWs which
have averaged expansion quantity Havg > 0, proving that classical counter-examples
to the theorem of Borde, Guth, and Vilenkin do exist. I conclude by introducing
conjectures concerning the relationship between geodesic completeness and inflation:
in particular, I speculate that if a spacetime is geodesically complete and non-trivial,
it must inflate!
ContributorsLesnefsky, Joseph Edward (Author) / Easson, Damien A (Thesis advisor) / Davies, Paul C (Thesis advisor) / Parikh, Maulik (Committee member) / Kotschwar, Brett (Committee member) / Arizona State University (Publisher)
Created2024