Advances in Synthetic Gauge Fields for Light Through Dynamic Modulation

Photons are weak particles that do not directly couple to magnetic fields. However, it is possible to generate a photonic gauge field by breaking reciprocity such that the phase of light depends on its direction of propagation. This non-reciprocal phase indicates the presence of an effective magnetic field for the light itself. By suitable tailoring of this phase it is possible to demonstrate quantum effects typically associated with electrons, and as has been recently shown, non-trivial topological properties of light. This paper reviews dynamic modulation as a process for breaking the time-reversal symmetry of light and generating a synthetic gauge field, and discusses its role in topological photonics, as well as recent developments in exploring topological photonics in higher dimensions.Comment: 20 pages, 3 figure

Asteroseismology and pulsation timing of the A-type stars observed by Kepler.

The A-type stars are arguably some of the most diverse stars found across the HR diagram, encompassing a wide range of physics, including rotation, pulsation, magnetic interactions, and chemical peculiarities. In this thesis, I develop a series of frameworks and tools to investigate a subset of the A-type stars: the delta Scuti and rapidly oscillating Ap (roAp) type stars, primarily using data from the Kepler and TESS space missions. I discuss the roAp stars within the context of the Kepler mission and identify six new members by exploiting irregularities in the sampling cadence. I then provide methods for the precise calculation of luminosities for A-type stars and apply them to the Kepler delta Scuti sample to improve the observational instability strip. I extend this work to a new class of young, high frequency delta Scuti stars discovered in the TESS data, which possess stable and regularly spaced modes, opening them up as potential candidates for mode identification via asteroseismology. I develop a framework for analysing delta Scuti stars in binary systems, through timing of their pulsations, and provide an open-source package to facilitate their analysis. Following this, I search for transits around the delta Scuti stars by iteratively subtracting their pulsations and identify three possible candidates in the Kepler data. Finally, I discuss the eclipsing binaries in the context of the inverse problem, and detail tested methods to rapidly obtain orbital parameters from the light curve with no prior knowledge

Uso de jogos digitais no aprimoramento da aprendizagem escolar no ensino fundamental II no Brasil

Dissertação de mestrado, Educação (Área de Especialidade em Educação e Tecnologias Digitais), 2022, Universidade de Lisboa, Instituto de EducaçãoEsta pesquisa descreve de que modo podem ser utilizados jogos digitais na aprendizagem escolar no ensino fundamental II, baseado nas diretrizes da BNCC no Brasil, pela análise da estratégia pedagógica aplicada no projeto Desafio Escolar - Edição STHEM. O projeto permitiu evidenciar as características que geram maior engajamento considerando o uso de tecnologias digitais e afinidade com jogos digitais, buscando estes recursos também na escola. A investigação estruturou-se sob a forma de um estudo de caso, com análise documental da iniciativa, veiculada digitalmente de forma gratuita, e procurou responder às seguintes questões de investigação: Como se caracteriza, do ponto de vista teóricoconceitual, a utilização de jogos digitais de acordo com a metodologia aprendizagem baseada em jogos digitais? Como se caracteriza um caso de aplicação do uso de jogos digitais como estratégia de aprendizagem em disciplinas do currículo escolar no ensino fundamental II? Quais foram os recursos educacionais digitais, presentes no caso em estudo, com maior e menor utilização por parte dos alunos? Foi realizada a análise da estratégia de aprendizagem do projeto Desafio Escolar - Edição STHEM e as variáveis monitoradas na plataforma digital foram categorizadas pelo tipo e uso de recursos educacionais digitais, buscando identificar qual recurso mais utilizado pelos estudantes, apresentando predominância de engajamento nas videoaulas e constância de acompanhamento dos conteúdos, indicando um possível modelo de aplicação de jogos digitais como estratégia pedagógica replicável com outros jogos e áreas do conhecimento por meio de tecnologias digitais.This research describes how digital games can be used in school learning in elementary II, based on the BNCC guidelines in Brazil, by analyzing the pedagogical strategy applied in the School Challenge project - STHEM Edition. The project allowed to highlight the characteristics that generate greater engagement considering the use of digital technologies and affinity with digital games, seeking these resources also at school. The research was structured in the form of a case study, with documentary analysis of the initiative, broadcasted digitally for free, and sought to answer the following research questions: How is the use of digital games characterized, from a theoretical and conceptual point of view, according to the methodology of game-based learning? How can we characterize a case of application of the use of digital games as a learning strategy in subjects of the school curriculum in elementary school II? Which were the digital educational resources, present in the case study, with more and less use by the students? The learning strategy analysis of the project Desafio Escolar - Edição STHEM, and its monitored variables on the digital platform, were categorized by the type and digital educational resources usage, seeking to identify which resource was most used by the students, showing a predominance of engagement in the video classes and consistency of content monitoring, indicating a possible model for the application of digital games as a pedagogical strategy that can be replicated with other games and areas of knowledge through digital technologies

Finding binaries from phase modulation of pulsating stars with \textit{Kepler}: VI. Orbits for 10 new binaries with mischaracterised primaries

Measuring phase modulation in pulsating stars has proved to be a highly successful way of finding binary systems. The class of pulsating main-sequence A and F variables known as delta Scuti stars are particularly good targets for this, and the \textit{Kepler} sample of these has been almost fully exploited. However, some \textit{Kepler} $\delta$ Scuti stars have incorrect temperatures in stellar properties catalogues, and were missed in previous analyses. We used an automated pulsation classification algorithm to find 93 new $\delta$ Scuti pulsators among tens of thousands of F-type stars, which we then searched for phase modulation attributable to binarity. We discovered 10 new binary systems and calculated their orbital parameters, which we compared with those of binaries previously discovered in the same way. The results suggest that some of the new companions may be white dwarfs.Comment: 8 pages, 6 figures that make liberal use of colou

Forward modeling the orbits of companions to pulsating stars from their light travel time variations

Mutual gravitation between a pulsating star and an orbital companion leads to a time-dependent variation in path length for starlight traveling to Earth. These variations can be used for coherently pulsating stars, such as the {\delta} Scuti variables, to constrain the masses and orbits of their companions. Observing these variations for {\delta} Scuti stars has previously relied on subdividing the light curve and measuring the average pulsation phase in equally sized subdivisions, which leads to under-sampling near periapsis. We introduce a new approach that simultaneously forward-models each sample in the light curve and show that this method improves upon current sensitivity limits - especially in the case of highly eccentric and short-period binaries. We find that this approach is sensitive enough to observe Jupiter mass planets around {\delta} Scuti stars under ideal conditions, and use gravity-mode pulsations in the subdwarf B star KIC 7668647 to detect its companion without radial velocity data. We further provide robust detection limits as a function of the SNR of the pulsation mode and determine that the minimum detectable light travel time amplitude for a typical Kepler {\delta} Scuti is around 2 s. This new method significantly enhances the application of light travel time variations to detecting short period binaries with pulsating components, and pulsating A-type exoplanet host stars, especially as a tool for eliminating false positives.Comment: 14 pages, accepted for publication in A

On the first δ Sct–roAp hybrid pulsator and the stability of p and g modes in chemically peculiar A/F stars

Abstract Strong magnetic fields in chemically peculiar A-type (Ap) stars typically suppress low-overtone pressure modes (p modes) but allow high-overtone p modes to be driven. KIC 11296437 is the first star to show both. We obtained and analysed a Subaru spectrum, from which we show that KIC 11296437 has abundances similar to other magnetic Ap stars, and we estimate a mean magnetic field modulus of 2.8 ± 0.5 kG. The same spectrum rules out a double-lined spectroscopic binary, and we use other techniques to rule out binarity over a wide parameter space, so the two pulsation types originate in one δ Sct–roAp hybrid pulsator. We construct stellar models depleted in helium and demonstrate that helium settling is second to magnetic damping in suppressing low-overtone p modes in Ap stars. We compute the magnetic damping effect for selected p and g modes, and find that modes with frequencies similar to the fundamental mode are driven for polar field strengths ≲ 4 kG, while other low-overtone p modes are driven for polar field strengths up to ∼1.5 kG. We find that the high-order g modes commonly observed in γ Dor stars are heavily damped by polar fields stronger than 1–4 kG, with the damping being stronger for higher radial orders. We therefore explain the observation that no magnetic Ap stars have been observed as γ Dor stars. We use our helium-depleted models to calculate the δ Sct instability strip for metallic-lined A (Am) stars, and find that driving from a Rosseland mean opacity bump at ∼5 × 104 K caused by the discontinuous H-ionization edge in bound-free opacity explains the observation of δ Sct pulsations in Am stars

A binary with a δ\delta~Scuti star and an oscillating red giant: orbit and asteroseismology of KIC9773821

We study the $\delta$ Scuti -- red giant binary KIC9773821, the first double-pulsator binary of its kind. It was observed by \textit{Kepler} during its four-year mission. Our aims are to ascertain whether the system is bound, rather than a chance alignment, and to identify the evolutionary state of the red giant via asteroseismology. An extension of these aims is to determine a dynamical mass and an age prior for a $\delta$ Sct star, which may permit mode identification via further asteroseismic modelling. We determine spectroscopic parameters and radial velocities (RVs) for the red giant component using HERMES@Mercator spectroscopy. Light arrival-time delays from the $\delta$ Sct pulsations are used with the red-giant RVs to determine that the system is bound and to infer its orbital parameters, including the binary mass ratio. We use asteroseismology to model the individual frequencies of the red giant to give a mass of $2.10^{+0.20}_{-0.10}$ M$_{\odot}$ and an age of $1.08^{+0.06}_{-0.24}$ Gyr. We find that it is a helium-burning secondary clump star, confirm that it follows the standard $\nu_{\rm max}$ scaling relation, and confirm its observed period spacings match their theoretical counterparts in the modelling code MESA. Our results also constrain the mass and age of the $\delta$ Sct star. We leverage these constraints to construct $\delta$ Sct models in a reduced parameter space and identify four of its five pulsation modes.Comment: Accepted for publication in MNRA

The effect of tides on near-core rotation: analysis of 35 Kepler γ\gamma Doradus stars in eclipsing and spectroscopic binaries

We systematically searched for gravity- and Rossby-mode period spacing patterns in Kepler eclipsing binaries with $\gamma$ Doradus pulsators. These stars provide an excellent opportunity to test the theory of tidal synchronisation and angular momentum transport in F- and A-type stars. We discovered 35 systems that show clear patterns, including the spectroscopic binary KIC 10080943. Combined with 45 non-eclipsing binaries with $\gamma$ Dor components that have been found using pulsation timing, we measured their near-core rotation rates and asymptotic period spacings. We find that many stars are tidally locked if the orbital periods are shorter than 10 days, in which the near-core rotation periods given by the traditional approximation of rotation (TAR) are consistent with the orbital period. Compared to the single stars, $\gamma$ Dor stars in binaries tend to have slower near-core rotation rates, likely a consequence of tidal spin-down. We also find three stars that have extremely slow near-core rotation rates. To explain these, we hypothesise that unstable tidally excited oscillations can transfer angular momentum from the star to the orbit, and slow the star below synchronism, a process we refer to as `inverse tides'.Comment: 13 pages, 10 figures, accepted by MNRA