1,720,971 research outputs found
Characterizing AU Microscopii Planets with Transit Timing Variations
No full textExoplanetary sciences is a relatively new field of study that has grown beyond just detection method to include, among other things, planetary and atmospheric characterizations. Recent missions such as Kepler, K2, and TESS has resulted in more than 5 000 planets being validated or confirmed, allowing us to delve deeply into studying the properties of these planets and their host systems. In this thesis, I present the Transit Timing Variations (TTVs) of AU Mic b and c and the validation of the candidate planet AU Mic d. AU Mic is a young (22 Myr) nearby exoplanetary system that exhibits excess TTVs that cannot be accounted for by the two known transiting planets b and c nor stellar activity. 37 transit observations (including one ASTEP, one Brierfield, 23 LCOGT, one PEST, three Spitzer, and eight TESS), three Rossiter-McLaughlin (R-M) observations (ESPRESSO, iSHELL, and SPIRou), and nine CHEOPS transit midpoint times are included in our TTV analyses. First, we use EXOFASTv2 to jointly model the transit light curves to obtain the transit midpoint times. We then construct an O–C diagram and model the TTVs with Exo-Striker. Second, we reproduce our results with an independent photodynamical analysis. We recover a TTV mass for AU Mic c of 10.8+2.3−2.2 M⊕. We compare the TTV-derived constraints to a recent radial-velocity (RV) mass determination. We also observe excess TTVs that do not appear to be consistent with the dynamical interactions of b and c alone, and do not appear to be due to spots or flares; therefore, we hypothesize the existence of a third planet AU Mic d that is driving the observed excess TTVs. I calculate d’s potential orbital periods by modeling the observed super-period in AU Mic b’s TTVs. Next, we explore several possible configurations for planet d, including having d be interior to b and having d be between b and c. We generate TTV log-likelihood periodograms to explore possible solutions for the orbital period of planet d and then follow those up with detailed TTV and RV MCMC modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, AU Mic b’s TTV super-period, stability tests, and Occam’s razor arguments regarding near-mean motion orbital resonance (MMR) chains and coplanarity of AU Mic system, the most-favored orbital period of AU Mic d is 12.73812 ± 0.00128 days (T_C,d = 2458333.32110 ± 0.35836 BJD), which puts the three planets near a 4:6:9 MMR. The mass for d from the most plausible case is M_d = 1.013 ± 0.146 M⊕, making this planet Earth-like in mass. This would make AU Mic the first known young star to host an Earth-mass planet. Lastly, I characterize AU Mic b’s atmosphere with Transit Depth Variations and found the effective radius of AU Mic b to be significantly smaller at 4.5 μm than at optical range, a phenomenon that is similarly seen in another young planet K2-33 b. The mass-radius analysis of AU Mic b indicates that it is comparable to that of a 10% H + He planet; however, since it’s atmosphere is known to be evaporating, AU Mic b is evolving into a smaller and denser planet over the next several Myrs or Gyrs. The presence of near-MMRs in a very young system implies that compact planetary systems can develop resonant chains very early on, which can quickly establish the stability of the systems. Additional TTV observations of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c. If AU Mic d does transit, it will serve as an incredibly valuable case study for characterizing the atmosphere of young terrestrial planets and understanding its evolution
CONFIRMATION AND VALIDATION OF TESS TRANSITING EXOPLANETS WITH THE ISHELL RADIAL VELOCITIES SPECTROMETER
Full text linkThe Precise Radial Velocity (PRV) technique is one of the most effective techniquesused to search for exoplanets and characterize them. We use the iSHELL spectrograph on NASA Infrared Telescope Facility (IRTF) to obtain follow-up PRV observations to continue monitoring and confirming Transiting Exoplanet Survey Satellite (TESS ) mission candidate planets orbiting cool and low mass stars. Observing cooler and lower-mass stars is unique because the reflex motion from orbiting exoplanets is larger, the transit depths are deeper, and the Habitable Zone (HZ) orbital periods are shorter. The importance of PRV follow-up observations is to confirm the orbital properties of the planets, determine their masses and bulk densities, look for evidence of additional planets, and constrain their eccentricities. My motivation for this study is to help NASA achieve its Level 1 goal. TESS was launched in Spring 2018 with a Level 1 mission requirement to search for small planets around nearby and bright stars with the goals of measuring the masses of 50 planets that are smaller than 4 Earth Radii (RL). While this may be sufficient to meet the primary TESS goal of determining the masses of 50 planets, it is not utilizing TESS to its full extent where many interesting targets will be left out. Therefore, ground-based PRVs help advance NASA’s Level 1 requirement. Our ground-based observations supplied us with the transits of the planets around their host stars which, in turn, provided an estimate of the orbital period and phase of a planet through which we can constrain the planetary mass. Thus, a combination of our PRVs and photometric transits will provide the radii and masses that drive the densities, which is the main scientific return needed for stars with planetary transits. In this thesis we confirm the validation of the TESS transiting exoplanet candidates with the iSHELL spectrograph at the NASA Infrared Telescope Facility (IRTF). We use a modified GP kernel to simulate and constrain the stellar activity in the stars and validate the discovery of a two-planet transiting system orbiting the TESS object of interest, (TOI) 560. We obtain follow-up spectroscopy and corresponding PRVs with iSHELL and the HIRES Spectrograph at Keck Observatory to validate the planetary nature of these signals, which we combine with the published Planet Finder Spectrograph (PFS) RVs from the Magellan Observatory. We estimate the age of the star and detect the masses of both planets. Next, we apply an optimization to our forward model technique that generates our PRVs. Optimization of the forward model is a unique approach and has not done before, where we deep dive to analyze each of its parameters to obtain the best Line Spread Function (LSF) model that fits our data and then we apply different techniques to produce PRVs. We selected TOI 461 as a model star to apply these optimizations because TOI 461 is a young, bright star and so is an excellent target for detailed characterization studies with JWST to constrain its composition and test theories of planet formation and evolution. We found that the deep telluric lines in our data tend to be poorly fit and have some residuals which causes a bias in our RVs. These RVs biases are called systematics. We applied new template processes to smooth the residuals of our forward model and change their deshifting. These new template processes helped improve the systematics and stabilized them. We implemented a new technique of clipping the saturated flux lines in our data because they motivate the systematics to appear. This clipping technique helped in mitigating the systematics and improved our PRVs. We trimmed the data at the edges of the spectral orders where data is noisy due to the lower signal-to-noise (SNR) ratio. We utilized a chunking approach to the spectrum by chopping it up into pieces and modeled each piece independently to test the behavior of the systematics in each part of iSHELL spectrograph. The trimming and chunking approaches both confirmed a variability in the distribution of our Line Spread Function (LSF), and so our LSF model is not constant across the star spectrum. We need a chromatic LSF that model the LSF width as a Gaussian changing slowly over the spectrum
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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