2,700 research outputs found
TESS exoplanet candidate follow-up with ground- and space-based instruments
La dĂ©couverte dâexoplanĂštes a connu une croissance quasi exponentielle au cours des trois derniĂšres dĂ©cennies. Nous savons dĂ©sormais que les systĂšmes dâexoplanĂštes sont la norme dans la galaxie et quâil existe une variĂ©tĂ© dâarchĂ©types de planĂštes qui ne correspondent pas Ă notre propre systĂšme solaire. Ces progrĂšs rapides sont dus en grande partie aux missions spatiales qui utilisent la mĂ©thode des transits pour trouver et caractĂ©riser de nouvelles exoplanĂštes. Kepler et, plus rĂ©cemment, le Transiting Exoplanet Survey Satellite (TESS) ont contribuĂ© Ă la majoritĂ© des exoplanĂštes confirmĂ©es ou candidates connues Ă ce jour. Les exoplanĂštes dĂ©couvertes par TESS sont particuliĂšrement prometteuses, car TESS a dĂ©libĂ©rĂ©ment ciblĂ© des Ă©toiles hĂŽtes brillantes pour faciliter lâanalyse spectroscopique dĂ©taillĂ©e de lâatmosphĂšre de leurs planĂštes. Bien que TESS soit trĂšs efficace pour identifier de nouveaux signaux de transit, un effort de suivi substantiel est nĂ©cessaire pour valider chaque nouvelle candidate et le succĂšs global de la mission TESS dĂ©pend fortement de lâobtention de ce suivi de la part dâobservatoires externes. Une attention particuliĂšre est souvent requise pour les planĂštes Ă longue pĂ©riode qui souffrent fortement des biais impliquĂ©s dans les recherches de transit. Si lâon peut surmonter les dĂ©fis observationnels supplĂ©mentaires, ces planĂštes constituent des bancs dâessai rares et prĂ©cieux pour Ă©tudier la physique et la chimie des atmosphĂšres plus froides.
Dans cette thĂšse, jâai collaborĂ© avec la communautĂ© de suivi des exoplanĂštes TESS sur plusieurs fronts en apportant des instruments prĂ©cĂ©demment inutilisĂ©s, en contribuant Ă lâeffort gĂ©nĂ©ral de vĂ©rification des candidates, ainsi quâen menant des Ă©tudes de validation et de confirmation de cibles difficiles Ă longue pĂ©riode. Nous avons adaptĂ© le rĂ©seau de tĂ©lĂ©objectifs Dragonfly (alias "Dragonfly"), conçu pour les cibles de faible luminositĂ© de surface, Ă lâobservation des transits dâexoplanĂštes. Jâai dĂ©veloppĂ© un nouveau mode dâobservation adaptĂ© aux transits et crĂ©Ă© des pipelines de planification, de traitement des donnĂ©es et dâanalyse. Nous avons atteint une prĂ©cision photomĂ©trique dâenviron 0,5 ppt dans des intervalles de 4 Ă 5 minutes sur la plage 9 < mV < 13, compĂ©titive avec dâautres observatoires au sol de classe 1â2 m. Nous avons Ă©galement dĂ©veloppĂ© un vaste programme dâobservation avec le satellite de surveillance des objets proches de la Terre (NEOSSat) couvrant 3 ans et 6 cycles dâobservation pour observer les transits dâexoplanĂštes de longue durĂ©e, qui reprĂ©sentent un dĂ©fi majeur Ă capturer avec des observatoires au sol. En utilisant ces deux instruments, nous avons fourni des observations pour le programme dâobservation de suivi des exoplanĂštes TESS (ExoFOP). GrĂące Ă mon travail dans ExoFOP, jâai dirigĂ© une publication de validation pour TOI-1221 b, une planĂšte sub-neptunienne de 2,9 rayons terrestres sur une orbite de 92 jours. Non seulement nous avons Ă©cartĂ© les scĂ©narios de faux positifs pour cette planĂšte tempĂ©rĂ©e Ă longue pĂ©riode, mais grĂące Ă notre analyse dĂ©taillĂ©e de 6 transits TESS et 2 dĂ©tections au sol, nous avons trouvĂ© des preuves de variations de synchronisation de transit qui pourraient indiquer une autre planĂšte cachĂ©e dans le systĂšme. Nous avons Ă©galement utilisĂ© NEOSSat pour rechercher un deuxiĂšme transit de TOI-2010 b, qui nâen montrait quâun seul dans les donnĂ©es TESS. En surveillant lâĂ©toile hĂŽte sur une fenĂȘtre dâincertitude de 7 jours, nous avons capturĂ© le transit et amĂ©liorĂ© considĂ©rablement notre connaissance de lâĂ©phĂ©mĂ©ride de la planĂšte. Jâai dirigĂ© lâarticle de confirmation sur cette planĂšte semblable Ă Jupiter avec une orbite de 142 jours, ajoutant une cible de faible insolation Ă la petite collection dâexoplanĂštes connues avec des pĂ©riodes supĂ©rieures Ă 100 jours et des Ă©toiles hĂŽtes suffisamment brillantes pour un suivi spectroscopique. En plus de diriger ces deux projets spĂ©cifiques, mes observations avec Dragonfly et NEOSSat ont jusquâĂ prĂ©sent contribuĂ© Ă 10 autres publications dont je suis co-auteur.Exoplanet discovery has undergone near-exponential growth over the last three decades. We now know exoplanet systems are the norm in the Galaxy and that a variety of planet archetypes exist that do not necessarily match our own Solar System. This rapid advancement is due in large part to space-based discovery missions utilizing the transit method to find and characterize new exoplanets. Kepler, and more recently, the Transiting Exoplanet Survey Satellite (TESS) have contributed the majority of confirmed or candidate exoplanets known today. The exoplanets discovered by TESS show particular promise, as TESS has deliberately targeted bright host stars to facilitate detailed spectroscopic analysis of their planetsâ atmospheres. While TESS is highly efficient at identifying new transit signals, substantial follow-up effort is required to validate each new candidate and the overall success of the TESS mission heavily depends on attaining this follow-up from external observatories. Special attention is often required for long-period planets that suffer heavily from the biases involved in transit searches. If one can overcome the added observational challenges, these planets provide rare and valuable testbeds to investigate cool-atmosphere physics and chemistry.
Through this thesis, I engaged with the TESS exoplanet follow-up community on several fronts by bringing previously unused instrument options to the endeavour, contributing to the general effort of candidate verification, as well as leading validation and confirmation studies of challenging long-period targets. We adapted the Dragonfly Telephoto Array (a.k.a. âDragonflyâ), designed for low-surface brightness targets, to the observation of exoplanet transits. I developed a new transient-appropriate observing mode and created scheduling, data processing, and analysis pipelines. We achieve a photometric precision floor of 0.5 ppt in 4â5-minute bins over the range 9 < mV < 13, competitive other 1â2 m class ground-based observatories. We also developed an extensive observing program with the Near-Earth Object Surveillance Satellite (NEOSSat) spanning 3 years and 6 observing cycles to observe long-duration exoplanet transits that provide a major challenge to capture with ground-based observatories. Using these two instruments, we provided follow-up observations for the TESS Exoplanet Follow-up Observing Program (ExoFOP). Through my work with ExoFOP, I led a validation publication for TOI-1221 b, a 2.9 Earth-radii sub-Neptune planet on a 92-day orbit. Not only do we rule out the false-positive scenarios for this long-period temperate planet, but through our detailed analysis of 6 TESS transits and 2 ground-based detections, we find evidence of transit timing variations that may indicate an additional hidden planet in the system. We also used NEOSSat to hunt for an elusive second transit of TOI-2010 b. By monitoring the host star over a 7-day uncertainty window, we caught the transit and vastly improved our knowledge of the planetâs ephemeris. I led the confirmation paper on this temperate Jupiter-like planet with a 142-day orbit, adding a low-insolation target to the small collection of known exoplanets with periods above 100 days and host stars bright enough for spectroscopic follow-up. Beyond leading these two specific projects, my observations with Dragonfly and NEOSSat have thus far contributed to 10 other publications for which I am co-author
Energy-Efficient Querying of Wireless Sensor Networks
Due to the distributed nature of information collection in wireless sensor networks and the inherent limitations of the component devices, the ability to store, locate, and retrieve data and services with minimum energy expenditure is a critical network function. Additionally, effective search protocols must scale efficiently and consume a minimum of network energy and memory reserves. A novel search protocol, the Trajectory-based Selective Broadcast Query protocol, is proposed. An analytical model of the protocol is derived, and an optimization model is formulated. Based on the results of analysis and simulation, the protocol is shown to reduce the expected total network energy expenditure by 45.5 percent to 75 percent compared to current methods. This research also derives an enhanced analytical node model of random walk search protocols for networks with limited-lifetime resources and time-constrained queries. An optimization program is developed to minimize the expected total energy expenditure while simultaneously ensuring the proportion of failed queries does not exceed a specified threshold. Finally, the ability of the analytical node model to predict the performance of random walk search protocols in large-population networks is established through extensive simulation experiments. It is shown that the model provides a reliable estimate of optimum search algorithm parameters
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Scanning tunneling microscopy of BiâSeâ and CuxBiâSeâ
textRecently, BiâSeâ was added to a new class of materials known as topological insulators. While several studies have provided tantalizing hints towards novel physical properties, such as backscatter suppression and spin-polarized transport, several concerns remain in actual materials. In particular, high defect densities, strong surface band bending, and potential fluctuations have been observed. Here, scanning tunneling microscopy and spectroscopy are used to reveal surface effects in BiâSeâ and CuxBiâSeâ. First, a detailed examination of defects in bulk-grown samples is described. Then, I provide an analysis of molecular beam epitaxy results, done in collaboration with colleague Yuxuan Chen. Following this, I provide a detailed study of individual point defects in Cu-doped BiâSeâ and examine how Cu is incorporated into the BiâSeâ lattice. Finally, through spectroscopic analysis, a novel depth-sensitive measurement of the local band bending field is developed. Furthermore, for the first time, fluctuations of the Dirac point can be correlated to specific near-surface defects, namely Se vacancies. These analyses provide valuable insights into the preparation of future samples for the investigation of topological insulators.Materials Science and Engineerin
A Novel 183GHz Subharmonic Schottky Diode Mixer
PhDThe technique of microwave .
limb sounding -from space
represents a very powerful tool for determining the atmospheric
processes involved in ozone depletion, the greenhouse effect, acid
rain, etc.. Unfortunately, the technology involved in producing
millimetric and submillimetric devices is highly complex, and
miniature. The power levels and environmental conditions
existing aboard spacecraft in present 'use, 5 differ from those
required by the low noise heterodyne receivers employed by the
Radio Astronomy community. Therefore, great effort has been
spent in the design of radiometers with limited power and weight
requirements, so that they can withstand the rigours of launch
and operation in space.
This thesis describes the design and construction of a
subharmonically pumped, double diode mixer which is now used
in an airborne atmospheric radiometer. The mixer power
requirement and rugged nature make it an ideal option for space
operation. The assembly of the millimetric circuit required the
development, of novel techniques which enabled the incorporation
of discrete circuit elements onto a single quartz substrate. This
allowed the physical testing of the millimetric circuit
independently of the RF block.
A detailed investigation into the `whiskering' technique was
carried out. It was thus possible to pinpoint errors that had
previously occurred in assembly and which had resulted in the
failure of a space flight device. With the adoption of quantified
procedures, devices constructed using the `whiskering' technique
were shown to be considerably more resilient than had previously
been thought.
The performance of the mixer is comparable with other
designs using Schottky diodes at room temperature (-1200K DSB)
and the local oscillator power requirement is easily met with a
single solid state source.
A simple theoretical analysis using the Seigel and Kerr
program was undertaken in conjunction with RF measurements
performed on a 65X scale model to determine steps required for
further improvement.Marconi Space Systems.
United Kingdom Meteorological Office and the SER
Interview with Chris Mann by Mike Hastings
Biographical NoteChristopher Mann was born December 19, 1962, in Augusta, Maine. His parents were Alden and Deana Mann. His father was a Maine native who worked for the State Bureau of Banks and Banking as the director of Securities. Chris grew up in Augusta, attended Cony High School and was graduated with a degree in political science from the University of Southern Maine. He worked on Joe Brennanâs 1988 congressional campaign. After that, Mary McAleney offered him a position doing research for the state legislature. He later moved to Washington, D.C., to work in the mailroom for Senator Mitchellâs office and eventually became a legislative correspondent. When Senator Mitchell retired, with the help of Mary McAleney, he went to work for the secretary of the Senate in the bill status office. After two years in that position, he was offered a place as a staffer in then Congressman Baldacciâs office. In 1999, he moved back to Maine to run the Bangor office for Congressman Baldacci. At the time of this interview, he held a position with the Maine Department of Transportation in the Bureau of Planning.
SummaryThis interview includes discussion: family and educational background; Augusta, Maine in the 1960s and 70s; State Bureau of Banks and Banking; University of Southern Maine; Public Interest Research Group (PIRG); interning at Senator Mitchellâs office in Portland, Maine; the General Agreement on Tariffs and Trade; Mary McAleney; Joe Brennanâs congressional campaign in 1988; the Maine state Senate; working for Senator Mitchell in Washington, D.C.; Maine people on staff in Washington D.C.; George Mitchell as majority leader; being a legislative correspondent; the Catastrophic Healthcare act; health care; Intermodal Surface Transportation Efficiency Act (ISTEA); Chris Mannâs responsibilities in Senator Mitchellâs office; the Democratic Party network; working for the secretary of the Senate; the Senate bills status office; working for the minority party; Republican Revolution; division in the Senate; living in rural Maine; Maine Department of Transportation; and Senator Mitchellâs current projects
F-theory and AdS_3/CFT_2
We construct supersymmetric AdS_3 solutions in F-theory, that is Type IIB
supergravity with varying axio-dilaton, which are holographically dual to 2d
N=(0,4) superconformal field theories with small superconformal algebra. In
F-theory these arise from D3-branes wrapped on curves in the base of an
elliptically fibered Calabi-Yau threefold Y_3 and correspond to strings in the
6d N=(1,0) theory obtained from F-theory on Y_3. The non-trivial fibration over
the wrapped curves implies a varying coupling of the N=4 Super-Yang-Mills
theory on the D3-branes. We compute the holographic central charges and show
that these agree with the field theory and with the anomalies of self-dual
strings in 6d. We complement our analysis with a discussion of the dual
M-theory solutions and a comparison of the central charges.Comment: 83 pages, v2: references added, typos correcte
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