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Decoding Exoplanetary System Architectures: Characterizing Multi-Planet Systems and their Host Stars
Get PDFIn this thesis, I investigate the architectures of exoplanetary systems, from detecting and characterizing individual planets to studying population-level trends and evaluating model predictiveness and accuracy. I particularly focus on complex multi-planet systems, leveraging the common formation and evolutionary environments of planets orbiting the same star to investigate system histories. I make use of space- and ground-based observations at both optical and near-infrared wavelengths to precisely and accurately determine both planet and stellar host parameters. I also investigate the accuracy of global models of planetary system architectures, revealing for the first time that empirical models of planetary systems based on the Kepler sample are not appropriately predictive for all planetary systems. These results highlight the need for both nuanced empirical models and analytical approaches that combine the statistical power of the observed sample of exoplanets and the physics encoded in planet formation models
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Detecting and Characterizing Small Planets in Diverse Environments
Get PDFOur ability to detect and characterize small planets in diverse environments is expanding rapidly with the development and continued improvement of the transit and radial velocity methods. Better models, instruments, and telescopes are producing greater planet yields and tighter planetary radius and mass constraints, which in turn provide new targets for atmospheric characterization and produce new insights on planet composition, formation, and evolution. In this thesis, I present work on the characterization and mass determination of small planets with the radial velocity method, the detection of new planets via the transit method, and the study of a planet’s atmosphere through transmission spectroscopy and its implications for planet formation and planet population features.First, I report on mass estimation and characterization of the long-period exoplanet Kepler- 538b. This sub-Neptune with a period of P = 81.7 days is the only planet known to be orbiting its Sun-like star (0.892 M⊙). Simultaneously modeling Kepler photometry and radial velocities (RVs) yields a semi-amplitude of 1.68 ± 0.39 m s−1 and a planet mass of 10.6 ± 2.5 M⊕, which made Kepler-538b the smallest planet beyond P = 50 days with an RV mass measurement at the time of publication. Precise mass measurements on long-period planets will not only directly address questions about the long-period planet population, but also draw comparisons and shed light on aspects of the short-period planet population like the planetary radius occurrence gap and the impact of high stellar irradiation on exoplanet compositions and atmospheres.Next, I discuss K2-136c, a sub-Neptune with a period of P = 17.3 days and the largest of three transiting planets orbiting a late-K dwarf (0.742 M⊙) in the young Hyades open cluster (650 ± 70 Myr). Collecting and analyzing RV data from the HARPS-N and ESPRESSO spectrographs jointly with photometry from the K2 and TESS space telescopes yielded an RV semi-amplitude of 5.46 ± 0.45 m s−1 for K2-136c, corresponding to a mass of 18.0 ± 1.7 M⊕. K2-136c is now the smallest planet to have a measured mass in an open cluster and one of the youngest planets ever with a mass measurement. As a result, this system adds an important new window into young small planet compositions, atmospheric mass loss constraints around young active stars, and planetary evolution at relatively unexplored ages.I then present the TATER planet detection pipeline and apply it to high-cadence photometry of 914 known planet systems observed during TESS Cycle 3. This work has led to the new validation of 4 short-period planets. This study provides independent modeling and vetting of hundreds of planet candidates while also expanding the known planet population and providing updated transit ephemerides and planet radii.Finally, I report on the atmospheric characterization of WASP-166b, a short-period super- Neptune (P = 5.44 d, Mp = 32.1 ± 1.6 M⊕, Rp = 7.1 ± 0.3 R⊕). WASP-166b is located near the edge of the Hot Neptune Desert, a sparse region of exoplanet parameter space at high stellar irradiation and intermediate planet radii. Using transmission spectroscopy of WASP-166b (two transit observations with the James Webb Space Telescope), initial analyses show evidence of H2O and CO2; no evidence of SO2, NH3, or a cloud deck; constraints on planetary metallicity and the C/O ratio; and a plausible formation pathway that includes planetesimal accretion followed by core erosion or photoevaporation. This in turn points to mechanisms that can create substellar or stellar C/O ratios and superstellar metallicities, like photoevaporation and core erosion, as feasible components of the formation of the Hot Neptune Desert
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Discovery and Demographics of Hot Planets Orbiting Hot Stars
Get PDFSurveys dedicated to detecting exoplanets via the transit and radial velocity methods have revolutionized our understanding of planet formation and evolution by revealing the the prevalence of planets orbiting close to their stars. Transit surveys have been especially groundbreaking due to their abilities to discover large quantities of planets with small orbital separations, which can they be further characterized via transmission spectroscopy, emission spectroscopy, and thermal phase curve observations to reveal details about their atmospheres and surfaces. In recent years, the Transiting Exoplanet Survey Satellite (TESS) has provided the opportunity to expand these techniques into entirely new regimes, due to its ability to search for transiting planets around a greater variety of stars and around brighter stars that are more amendable to follow-up observations. This thesis focuses on the utilization of TESS data to search for and study the demographics of these planets.First, I present TRICERATOPS, a tool designed to statistically validate transiting exoplanets and identify likely astrophysical false positives in TESS data. To statistically validate a transiting exoplanet is to confirm its planetary nature by ruling out plausible false positive scenarios, such as those that arise when multiple stars are blended together in the data. This is a particularly pertinent problem for TESS, which is equipped with relatively low-resolution cameras that often cannot distinguish light originating from individual stars, especially in crowded fields. I discuss the design and efficacy of TRICERATOPS, demonstrating that it is an effective tool for identifying the most promising planet candidates detected by TESS and prioritizing follow-up observations with both ground-based and space-based telescopes.Next, I use TRICERATOPS and an array of ground-based follow-up observations to validate 13 hot and potentially terrestrial planets detected by TESS. These planets are unlike any rocky bodies in the Solar System; they orbit their stars at distances of only a few stellar radii and are so highly irradiated that many are expected to have molten surfaces. Their high temperatures also mean that they emit infrared light at levels detectable by JWST. Emission spectroscopy and thermal phase curve observations of these worlds can reveal the presence and composition of an atmosphere, measure Bond albedo, and calculate heat redistribution properties. Prior to TESS, very few of these types of planets were known around bright stars amenable to JWST observations. This sample therefore facilitates the investigation of hot Earth-size worlds at a population level.Finally, I conduct a search for planets smaller than Saturn orbiting A-type stars. A-type stars, which are roughly twice as massive and nearly twice as hot as Sun-like stars, have historically been avoided by transit and radial velocity surveys due to their large radii and rapid rotation rates, which hinder our ability to detect planets around them. As a consequence, early transit surveys like the Kepler mission acquired very little data of these stars, limiting our understanding of planet demographics to stars like the Sun and cooler. By observing all bright stars across nearly the entire sky, TESS has provided the best opportunity yet to search for small planets orbiting relatively hot stars. Through this search, I discover and validate a single planet: HD 56414 b, a Neptune-size planet orbiting one of the hottest planet-hosting stars known to date on a 29-day orbital period. The orbital period of this planet is long compared to the typical planet detected by TESS, suggesting that Neptune-size planets with smaller orbital separations may not exist around A-type stars. I display that atmospheric photoevaporation due to high levels of near-ultraviolet radiation offers one possible explanation for this phenomenon. To test this hypothesis more robustly, I calculate the occurrence rate of small planets with orbital periods under 10 days around A-type stars. I demonstrate, for the first time, that sub-Saturns and sub-Neptunes are rarer around A-type stars than they are around their cooler counterparts. I also find evidence that super-Earths are as common or less common around A-type stars than cooler stars. These results suggest that small planets are unable to form at, migrate to, or survive at the small orbital separations probed by TESS around these hot stars. Overall, these findings significantly advance our understanding of how planets form and evolve around stars hotter than the Sun, providing a more holistic picture of planetary populations throughout the galaxy
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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