New contributions to algorithms and tools for the analysis of photometric and spectroscopic time-series in exoplanet searches

[eng] The current trend in exoplanet research focuses on the detection and characterisation of Earth-sized planets, and the study of their potential subtle and tenuous atmospheres. The aim of this thesis is the development of tools and simulation codes for the detection and characterisation of exoplanets by means of the indirect methods of radial velocities and transits. The structure of the thesis is two-fold. Firstly, we present a multidimensional extension to the well-known period search GLS code, which we dub MGLS (Multidimensional Generalized Lomb-Scargle periodogram). The analysis of a time-series periodogram of radial velocity data is the usual starting point to seek for periodic signals which then can be associated with the reflex Keplerian motion of a star caused by orbiting exoplanets. In the case of multiplanetary systems such analysis is usually carried out in an iterative fashion, known as prewhitening. This approach can diminish the significance and distort the parameters of periodic signals, and we aim to solve those limitations by introducing a multidimensional approach. Additionally, a robust criterion to determine the number of signals (dimensionality) in a time-series is presented. The new approach is more flexible and enhances the significance of multisignal detections and their multiplicity. It is further better capable to pinpoint the fit parameters and is able to compare models of different dimensionality. The MGLS code has been tested with real multiplanetary systems, showing its excellent performance in detectability. The code is publicly available to the community. The second part addresses the effects of rotationally-induced stellar activity on the photometric and spectroscopic observables. The properties, distribution, and evolution of inhomogeneities on the surface of active stars, such as dark spots and bright faculae, significantly influence the determination of the parameters of an orbiting exoplanet. The chromatic effect they have on transmission spectroscopy, for example, could affect the analysis of data from future space missions such as James Webb Space Telescope (JWST) and Ariel. To quantify and mitigate the effects of those surface phenomena, we developed a fast modelling approach to derive the surface distribution and properties of active regions by modelling simultaneous multi-wavelength time-series observables. We present an upgraded version of the StarSim code, now featuring the capability to solve the inverse problem and derive the properties of the stars and their active regions by modelling time-series data. The multiband photometric inverse problem is both analytically and numerically discussed, as well as a broad analysis of the degeneracies found in the inversion process. As a test case, we analyse a BVRI multiband ground photometry dataset of the exoplanet host star WASP-52. From the results, we further simulated the chromatic contribution of surface phenomena on the observables of its transiting planet. We demonstrate that by using contemporaneous ground-based multiband photometry of an active star, it is possible to reconstruct the parameters and distribution of active regions over time, thus making it feasible to quantify the chromatic effects on the planetary radii measured with transit spectroscopy and mitigate them by about an order of magnitude. The obtained results show it is possible to accurately characterise the heterogeneous stellar surface up to a precision of a few parts in 10^5 and validate the scientific case of space missions like Ariel, designed for exoplanetary transmission spectroscopy.[cat] L'interès actual en la recerca en exoplanetes rau en la detecció de planetes cada cop més petits on els senyals són estadísticament poc significatius, particularment en l'estudi de les seves atmosferes. La tesi té com a objectiu el disseny i desenvolupament d'eines i codis sofisticats per a la detecció i caracterització de les propietats d'exoplanetes mitjançant l'ús de les tècniques de velocitat radial i trànsits, i es compon de dues parts diferenciades: la primera, tracta la generalització d'una eina de detecció de periodicitats molt popular en aquest camp (GLS). S'ha desenvolupat una versió multidimensional, que anomenem MGLS (Multidimensional Generalized Lomb-Scargle periodogram), que permet l'ajust simultani d'un nombre arbitrari de senyals, de manera que millora notablement la detectabilitat de senyals compostos, i evita els problemes derivats del filtratge quan es fa servir el procediment seqüencial, com falsos positius/negatius. Addicionalment es presenta un procediment robust per a la determinació del nombre de senyals (dimensionalitat). La segona part, tracta els efectes de l'activitat estel·lar sobre les mesures de velocitat radial i fotometria. L'activitat magnètica superficial en forma de taques i fàcules constitueix superfícies heterogènies, que amb la rotació de l'estrella, produeixen variacions d'intensitat i cromàtiques en els observables. S'ha desenvolupat un codi ràpid per a la modelització física de l'activitat induïda per rotació de taques, prenent com a base una versió de codi preexistent. En la versió StarSim 2, permet dur a terme el problema invers per determinar l'estat de la superfície més probable donades unes observacions fotomètriques. També es desenvolupa una formulació analítica per al problema invers multibanda i s'analitzen detalladament les degeneracions existents en el problema. L'esquema d'inversió i el codi s'aplica a un conjunt de dades multifiltre (BVRI) de l'estrella WASP-52, i es simulen els efectes cromàtics del model d'activitat ajustat sobre els seus trànsits, com procedir per corregir-los per assolir una precisió d'unes poques parts en cent mil, i per tant validar el cas científic que sustenta la missió Ariel per a l'anàlisi d'atmosferes exoplanetàries per espectroscòpia de transmissió

Sensor placement for fault diagnosis based on structural models: application to a fuel cell stak system

The present work aims to increase the diagnosis systems capabilities by choosing the location of sensors in the process. Therefore, appropriate sensor location will lead to better diagnosis performance and implementation easiness. The work is based on structural models ands some simplifications are considered in order to only focus on the sensor placement analysis. Several approaches are studied to solve the sensor placement problem. All of them find the optimal sensor configuration. The sensor placement techniques are applied to a fuel cell stack system. The model used to describe the behaviour of this system consists of non-linear equations. Furthermore, there are 30 candidate sensors to improve the diagnosis specifications. The results obtained from this case study are used to strength the applicability of the proposed approaches.El present treball té per objectiu incrementar les prestacions dels diagnosticadors mitjançant la localització de sensors en el procés. D'aquesta manera, instal·lant els sensors apropiats s'obtenen millors diagnosticador i més facilitats d'implementació. El treball està basat en models estructurals i contempla una sèrie de simplificacions per tal de entrar-se només en la problemàtica de la localització de sensors. S'utilitzen diversos enfocs per tal de resoldre la localització de sensors, tot ells tenen com objectiu trobar la configuració òptima de sensors. Les tècniques de localització de sensors són aplicades a un sistema basat en una pila de combustible. El model d'aquest sistema està format per equacions no lineals. A més, hi ha la possibilitat d'instal·lar fins a 30 sensors per tal de millorar la diagnosis del sistema. Degut a aquestes característiques del sistema i del model, els resultats obtinguts mitjançant aquest cas d'estudi reafirmen l'aplicabilitat dels mètodes proposats.Postprint (published version

Towards a generic optimal co-design of hardware architecture and control configuration for interacting subsystems

In plants consisting of multiple interacting subsystems, the decision on how to optimally select and place actuators and sensors and the accompanying question on how to control the overall plant is a challenging task. Since there is no theoretical framework describing the impact of sensor and actuator placement on performance, an optimization method exploring the possible configurations is introduced in this paper to find a trade-off between implementation cost and achievable performance. Moreover, a novel model-based procedure is presented to simultaneously co-design the optimal number, type and location of actuators and sensors and to determine the corresponding optimal control architecture and accompanying control parameters. This paper adds the optimization of the control architecture to the current state-of-the-art. As an optimization output, a Pareto front is presented, providing insights on the optimal total plant performance related to the hardware and control design implementation cost. The proposed algorithm is not focused on one particular application or a specific optimization problem, but is instead a generally applicable method and can be applied to a wide range of applications (e.g., mechatronic, electrical, thermal). In this paper, the co-design approach is validated on a mechanical setup

Sensor Placement for Fault Diagnosis Performance Maximization under Budgetary Constraints

This paper presents a strategy based on fault diagnosability maximization to optimally locate sensors in complex systems. The goal is to characterize and determine a sensor configuration that guarantees a maximum degree of diagnosability and does not exceed a maximum sensor configuration cost. The strategy is based on the structural system model. Structural analysis is a powerful tool for dealing with complex nonlinear systems. The proposed approach is successfully applied to a Fuel Cell Stack System

Efficient optimal sensor placement for model-based FDI using and incremental algorithm

Abstract-The problem of optimal sensor placement for FDI consists in determining the set of sensors that minimizes a pre-defined cost function satisfying at the same time a pre-established set of FDI specifications for a given set of faults. Existing approaches are mainly based on formulating an optimization problem once the sets of all possible ARRs has been generated, considering all possible candidate sensors installed. However, the associated computational complexity is exponential with the number of possible sensors. The main goal of this paper is to propose an incremental algorithm for FDI sensor placement that tries to avoid the computational burden. To show the effectiveness of this approach, an application based on a fuel-cell system is proposed

Modelling the photosphere of active stars for planet detection and characterizaton

Context. Stellar activity patterns are responsible for jitter effects that are observed at different timescales and amplitudes in the measurements obtained from photometric and spectroscopic time series observations. These effects are currently in the focus of many exoplanet search projects, since the lack of a well-defined characterization and correction strategy hampers the detection of the signals associated with small exoplanets. Aims. Accurate simulations of the stellar photosphere based on the most recent available models for main-sequence stars can provide synthetic photometric and spectroscopic time series data. These may help to investigate the relation between activity jitter and stellar parameters when considering different active region patterns. Moreover, jitters can be analysed at different wavelength scales (defined by the passbands of given instruments or space missions) to design strategies to remove or minimize them. Methods. We present the StarSim tool, which is based on a model for a spotted rotating photosphere built from the integration of the spectral contribution of a fine grid of surface elements. The model includes all significant effects affecting the flux intensities and the wavelength of spectral features produced by active regions and planets. The resulting synthetic time series data generated with this simulator were used to characterize the effects of activity jitter in extrasolar planet measurements from photometric and spectroscopic observations. Results. Several cases of synthetic data series for Sun-like stars are presented to illustrate the capabilities of the methodology. A specific application for characterizing and modelling the spectral signature of active regions is considered, showing that the chromatic effects of faculae are dominant for low-temperature contrasts of spots. Synthetic multi-band photometry and radial velocity time series are modelled for HD 189733 by adopting the known system parameters and fitting for the map of active regions with StarSim. Our algorithm reproduces both the photometry and the radial velocity (RV) curves to good precision, generally better than the studies published to date. We evaluate the RV signature of the activity in HD 189733 by exploring a grid of solutions from the photometry. We find that the use of RV data in the inverse problem could break degeneracies and allow for a better determination of some stellar and activity parameters, for example, the configuration of active regions, the temperature contrast of spots, and the amount of faculae. In addition, the effects of spots are studied for a set of simulated transit photometry, showing that these can introduce variations in Rp/R∗ measurements with a spectral signature and amplitude that are very similar to the signal of an atmosphere dominated by dust

Reducing energy consumption in an industrial process by using model predictive control

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this paper, we propose to use Model Predictive Control techniques to reduce the energy consumption in an industrial process by incorporating energy consumption restrictions in the problem formulation. We propose to use a Model Predictive Control supervisor to calculate the optimum references for simple control loops regulated by individual PID controllers. The results obtained are compared against those obtained when a traditional control strategy exclusively based on PID controllers was used. By using this supervisory control strategy a reduction on energy consumption of about 10% was achieved.Peer ReviewedPostprint (author's final draft

Effectiveness and safety of anti-CGRP monoclonal antibodies in patients over 65 years: a real-life multicentre analysis of 162 patients

Background Anti-CGRP monoclonal antibodies have shown notable effectiveness and tolerability in migraine patients; however, data on their use in elderly patients is still lacking, as clinical trials have implicit age restrictions and real-world evidence is scarce. In this study, we aimed to describe the safety and effectiveness of erenumab, galcanezumab and fremanezumab in migraine patients over 65 years old in real-life. Methods In this observational real-life study, a retrospective analysis of prospectively collected data from 18 different headache units in Spain was performed. Migraine patients who started treatment with any anti-CGRP monoclonal antibody after the age of 65 years were included. Primary endpoints were reduction in monthly migraine days after 6 months of treatment and the presence of adverse effects. Secondary endpoints were reductions in headache and medication intake frequencies by months 3 and 6, response rates, changes in patient-reported outcomes and reasons for discontinuation. As a subanalysis, reduction in monthly migraine days and proportion of adverse effects were also compared among the three monoclonal antibodies. Results A total of 162 patients were included, median age 68 years (range 65-87), 74.1% women. 42% had dyslipidaemia, 40.3% hypertension, 8% diabetes, and 6.2% previous cardiovascular ischaemic disease. The reduction in monthly migraine days at month 6 was 10.17.3 days. A total of 25.3% of patients presented adverse effects, all of them mild, with only two cases of blood pressure increase. Headache and medication intake frequencies were significantly reduced, and patient-reported outcomes were improved. The proportions of responders were 68%, 57%, 33% and 9% for reductions in monthly migraine days >= 30%,>= 50%,>= 75% and 100%, respectively. A total of 72.8% of patients continued with the treatment after 6 months. The reduction in migraine days was similar for the different anti-CGRP treatments, but fewer adverse effects were detected with fremanezumab (7.7%). Conclusions Anti-CGRP mAbs are safe and effective treatments in migraine patients over 65 years old in real-life clinical practice

A chemical survey of exoplanets with ARIEL

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio

EarthFinder Probe Mission Concept Study: Characterizing nearby stellar exoplanet systems with Earth-mass analogs for future direct imaging

EarthFinder is a NASA Astrophysics Probe mission concept selected for study as input to the 2020 Astrophysics National Academies Decadal Survey. The EarthFinder concept is based on a dramatic shift in our understanding of how PRV measurements should be made. We propose a new paradigm which brings the high precision, high cadence domain of transit photometry as demonstrated by Kepler and TESS to the challenges of PRV measurements at the cm/s level. This new paradigm takes advantage of: 1) broad wavelength coverage from the UV to NIR which is only possible from space to minimize the effects of stellar activity; 2) extremely compact, highly stable, highly efficient spectrometers (R>150,000) which require the diffraction-limited imaging possible only from space over a broad wavelength range; 3) the revolution in laser-based wavelength standards to ensure cm/s precision over many years; 4) a high cadence observing program which minimizes sampling-induced period aliases; 5) exploiting the absolute flux stability from space for continuum normalization for unprecedented line-by-line analysis not possible from the ground; and 6) focusing on the bright stars which will be the targets of future imaging missions so that EarthFinder can use a ~1.5 m telescope