1,721,193 research outputs found
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Improving Cosmological Utility of Type Ia Supernovae through Physics and Big Data
Full text linkAfter correcting for their light-curve shape and color, Type Ia supernovae (SNe Ia) are precise cosmological distance indicators. However, there remains a non-zero intrinsic scatter in the differences between measured distance and distances inferred from a cosmological model (i.e., Hubble residuals). We have found that Hubble residuals are correlated with different properties of SN Ia host galaxies (e.g., mass, star-formation rate, and metallicity). Cosmological analyses attempt to correct for these effects empirically without any physical knowledge of the progenitor system, potentially introducing a bias. In this thesis, I detail several projects aimed at uncovering the dominant physical sources of intrinsic scatter. First, I will present Kaepora, a relational database for SN Ia observations containing 4975 public spectra of 777 SNe Ia. We have significantly improved this data set by inspecting these spectra for quality, removing galactic emission lines and cosmic rays, generating variance spectra, and correcting for the reddening caused by both MW and host-galaxy dust. Using this large homogenized sample, we produce composite spectra that have been precisely controlled for phase and light-curve shape. These composite spectra reproduce known trends with other optical properties of SNe Ia, and by controlling for these effects, they can be used to investigate a wide parameter space. Critically, with these methods I will show that SN Ia distances can potentially be improved with the knowledge of their ejecta velocities. I will then describe late time observations of the UV-flashing high-velocity SN Ia 2019yvq. We identify strong Calcium emission in the nebular spectrum of this SN and argue that this indicates SN 2019yvq was likely the result of a sub-Chandrasekhar mass double-detonation explosion. It is possible that 2019yvq-like SNe contribute to our cosmological samples, and the presence of multiple progenitor channels could be a source of Hubble residual intrinsic scatter. A better understanding of SN Ia progenitor environments (which may correlate with progenitor channel) could help us discern the relative contributions of multiple progenitor channels in cosmological samples. Finally, I will present preliminary results from the Foundation/Swope host galaxy survey (a project which has spanned my entire graduate career). We have obtained optical spectroscopy for 372 out of 517 total SN host galaxies in the Foundation and Swope combined cosmological SN sample (the largest low-z sample). The mass-metallicity relationship of our preliminary sample is consistent with similar samples and contains some of the lowest mass galaxies studied in a cosmological sample. Our sample also shows evidence for a "metallicity-step" using measurements from both the galaxy nucleus and the supernova location. With the full sample, we hope to constrain the functional form of this relationship and better understand the underlying physical cause of the empirical host-galaxy correction
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Unlocking Time-domain & Multimessenger Astrophysics and the Discovery of the First Optical Counterpart to a Gravitational Wave Source
Full text linkThe modern study of astrophysics is being transformed by advances across multiple fronts. New fast, wide, deep, and multi-color surveys are pushing into novel parameter spaces and generating an exponentially growing volume of data. Simultaneously, the first direct detection of gravitational waves (GWs) in 2015 has created a global race to search for their luminous counterparts. Here I present three major results that reside at the intersection of this new science and the methods, algorithms, and technology that enable it. The first is {\tt YSE-PZ}, a transient survey management platform that enables three major transient surveys: the Young Supernova Experiment, the Keck Infrared Transient Survey, and the Swope Supernova Survey. Second, I describe the discovery of the first optical counterpart to gravitational wave source, the kilonova (KN) SSS17a/AT 2017gfo. Discovering the KN and localizing it to the galaxy NGC~4993 paved the way for all the science that followed: it confirmed that there are electromagnetic (EM) counterparts to GWs, it allowed a redshift of NGC 4993 to be combined with the GW-derived luminosity distance to GW170817 and enabled the first standard siren measurement of H, and lead to the ability for rapid follow-up observations to confirm that binary neutron star (BNS) mergers are prolific astrophysical sites for the synthesis of the -process elements. Finally, I present a new ultraviolet, optical, and infrared search for the electromagnetic (EM) counterpart to GW190425, the second-ever BNS merger discovered by the LIGO-Virgo-KAGRA Collaboration (LVK). Intrinsic properties and observational limitations meant that any counterpart to GW190425 would be much harder to discover than SSS17a was, and neither our search, nor the broader EM community's search, discovered a credible counterpart. I contrast this speculative counterpart to SSS17a and discuss how KN diversity complicates our picture of heavy-element nucleosynthesis. I perform a combined analysis of the EM community's search for GW190425 using a new GW search and analysis tool called {\tt Teglon}. Through {\tt Teglon}, I calculate the most comprehensive upper limits on this potential EM counterpart to GW190425, as well as discuss opportunities for enhancing the community's coordination for the next BNS GW event in the LVK's fourth observing run and beyond
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Advancing Type Ia Supernova Science: The Swope Supernova Survey and Relationships Between i-Band Light Curve Diversity and Spectral Parameters
Full text linkSince the beginning of the modern telescope, astronomers have thought of new surveys and methods to study astrophysical phenomena. In this dissertation, I present the Swope Supernova Survey, a low-redshift photometric survey at Las Campanas Observatory, Chile, detailing its motivation, methodology, and significant contributions to transient astrophysics. I also highlight my vital contributions to the survey and science enabled. Since its inception in 2016, the survey has established itself as a critical resource for the study of transients below +30◦ declination, covering a wide wavelength range (u to i band), precise calibration, and high observing cadences. I specifically focus on the first Type Ia Supernova (SN Ia) data release, an effort that I led to provide over 100 high-cadence light curves in five photometric bands. This dataset enhances low-redshift SN Ia samples and opens the path for future work that will significantly contribute to SN cosmology. Finally, I introduce a novel parametrization of i-band light-curve diversity. I present the ∆m1 − ∆m2 parameter, which captures differences between the data and model at the i-band secondary maximum and minimum. Strong correlations are identified between this parameter and key spectral features, such as Ca II pEW0 and Si II v0, highlighting the role of spectral variations in shaping i-band light curves. This work also shows how these variations impact SN Ia composite spectra and synthetic photometry, revealing limitations in the widely used SALT3 SN Ia model. This dissertation highlights the importance of combining photometric and spectroscopic analyses to advance our understanding of SNe Ia, further exploring connections between SN Ia spectral features, i-band light-curve morphology and diversity, physical processes, environmental dependencies, and the accuracy of SNe Ia as precise cosmological distance indicators
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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