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J. Fernandes

Publications and source records attributed to J. Fernandes.

At least 19 recordsLinked to original sources
arXiv2023

Data Preservation in High Energy Physics

Data preservation is a mandatory specification for any present and future experimental facility and it is a cost-effective way of doing fundamental research by exploiting unique data sets in the light of the continuously increasing theoretical understanding. This document summarizes the status of data preservation in high energy physics. The paradigms and the methodological advances are discussed from a perspective of more than ten years of experience with a structured effort at international level. The status and the scientific return related to the preservation of data accumulated at large collider experiments are presented, together with an account of ongoing efforts to ensure long-term analysis capabilities for ongoing and future experiments. Transverse projects aimed at generic solutions, most of which are specifically inspired by open science and FAIR principles, are presented as well. A prospective and an action plan are also indicated.

hep-ex↗
arXiv2022

Automatically Assessing Students Performance with Smartphone Data

As the number of smart devices that surround us increases, so do the opportunities to create smart socially-aware systems. In this context, mobile devices can be used to collect data about students and to better understand how their day-to-day routines can influence their academic performance. Moreover, the Covid-19 pandemic led to new challenges and difficulties, also for students, with considerable impact on their lifestyle. In this paper we present a dataset collected using a smartphone application (ISABELA), which include passive data (e.g., activity and location) as well as self-reported data from questionnaires. We present several tests with different machine learning models, in order to classify students' performance. These tests were carried out using different time windows, showing that weekly time windows lead to better prediction and classification results than monthly time windows. Furthermore, it is shown that the created models can predict student performance even with data collected from different contexts, namely before and during the Covid-19 pandemic. SVMs, XGBoost and AdaBoost-SAMME with Random Forest were found to be the best algorithms, showing an accuracy greater than 78%. Additionally, we propose a pipeline that uses a decision level median voting algorithm to further improve the models' performance, by using historic data from the students to further improve the prediction. Using this pipeline, it is possible to further increase the performance of the models, with some of them obtaining an accuracy greater than 90%.

cs.HC↗
arXiv2022

Social Sensing and Human in the Loop Profiling during Pandemics: the Vitoria application

As the number of smart devices that surround us increases, so do the opportunities to leverage them to create socially- and context-aware systems. Smart devices can be used for better understanding human behaviour and its societal implications. As an example of a scenario in which the role of socially aware systems is crucial, consider the SARS-CoV-2 pandemic. In this paper we present an innovative Humanin-The-Loop Cyber Physical system that can collect passive data from people, such as physical activity, sleep information, and discrete location, as well as collect self-reported data, and provide individualised user feedback. In this paper, we also present a three and a half months field trial implemented in Portugal. This trial was part of a larger scope project that was supported by the Portuguese National Health System, to evaluate the indicators and effects of the pandemic. Results concerning various applications usage statistics are presented, comparing the most used applications, their objective and their usage pattern in work/non-work periods. Additionally,the time-lagged cross correlation between some of the collected metrics, Covid events, and media news, are explored. This type of applications can be used not only in the context of Covid but also in future pandemics, to assist individuals in self-regulation of their contagion risk, based on personalized information, while also function as a means for raising self-awareness of risks related to psychological wellbeing.

cs.HC↗
arXiv2018

Software tool for automatic detection of solar plages in the Coimbra Observatory spectroheliograms

Full-disk spectroheliograms have been taken in Coimbra on a daily basis since 1926 in the Ca II K-line (K1 and K3). Later, in 1989, with the upgrade of the equipment it was possible to start the observations in the H-alpha line. The spectroheliograms of Coimbra constitutes a huge dataset of solar images, which requires an efficient automatic tool to detect and analyse solar activity features. This work presents a mathematical morphology approach applied to the CaII K3 series. The objective is to create a tool based on the segmentation by watershed transform combined with other morphological operators to detect automatically and analyse chromospheric plages during the solar cycle 24. The tool is validated by comparing its results for cycle 23 with those presented by Dorotovic et al. (2007, 2010). The results obtained are in very good agreement with those, including on images obtained in non-ideal meteorological conditions (eg. some clouds in sky). The results were also qualitatively compared with the results obtained through the application of ASSA model to SDO HMI magnetograms.

astro-ph.SR↗
arXiv2017

Jupiter's North Equatorial Belt expansion and thermal wave activity ahead of Juno's arrival

The dark colors of Jupiter's North Equatorial Belt (NEB, $7-17^\circ$N) appeared to expand northward into the neighboring zone in 2015, consistent with a 3-5 year cycle of activity in the NEB. Inversions of thermal-IR imaging from the Very Large Telescope revealed a moderate warming and reduction of aerosol opacity at the cloud tops at $17-20^\circ$N, suggesting subsidence and drying in the expanded sector. Two new thermal waves were identified during this period: (i) an upper tropospheric thermal wave (wavenumber 16-17, amplitude 2.5 K at 170 mbar) in the mid-NEB that was anti-correlated with haze reflectivity; and (ii) a stratospheric wave (wavenumber 13-14, amplitude 7.3 K at 5 mbar) at $20-30^\circ$N. Both were quasi-stationary, confined to regions of eastward zonal flow, and are morphologically similar to waves observed during previous expansion events.

astro-ph.EP↗
arXiv2013

Li depletion in solar analogues with exoplanets: Extending the sample

We want to study the effects of the formation of planets and planetary systems on the atmospheric Li abundance of planet host stars. In this work we present new determinations of lithium abundances for 326 Main Sequence stars with and without planets in the T$_\mathrm{eff}$ range 5600-5900 K. 277 stars come from the HARPS sample, the remaining targets have been observed with a variety of high resolution spectrographs. We confirm significant differences in the Li distribution of solar twins (T$_\mathrm{eff}$ = T$_{\odot} \pm$ 80 K, log g = log g$_{\odot}$ $\pm$ 0.2 and [Fe/H] = [Fe/H]$_{\odot} \pm$ 0.2): the full sample of planet host stars (22) shows Li average values lower than "single" stars with no detected planets (60). If we focus in subsamples with narrower ranges in metallicity and age, we observe indications of a similar result though it is not so clear for some of the studied subsamples. Furthermore, we compare the observed spectra of several couples of stars with very similar parameters which show different Li abundances up to 1.6 dex. Therefore we show that neither age, nor mass nor metallicity of a parent star is the only responsible for enhanced Li depletion in solar analogues. We conclude that another variable must account for that difference and suggest that this could be the presence of planets which causes additional rotationally induced mixing in the external layers of planet host stars. Moreover, we find indications that the amount of depletion of Li in planet host solar-type stars is higher when the planets are more massive than Jupiter.

astro-ph.EP↗
arXiv2013

Temporal Evolution of Sunspot Areas and Estimation of Related Plasma Flows

The increased amount of information provided by ongoing missions such as the Solar Dynamics Observatory (SDO) represents a great challenge for the understanding of basic questions such as the internal structure of sunspots and how they evolve with time. Here, we contribute with the exploitation of new data, to provide a better understanding of the separate growth and decay of sunspots, umbra and penumbra. Using fuzzy sets to compute separately the areas of sunspot umbra and penumbra, the growth and decay rates for active regions NOAA 11117, NOAA 11428, NOAA 11429, and NOAA 11430 are computed, from the analysis of intensitygrams obtained by the Helioseismic and Magnetic Imager onboard SDO. A simplified numerical model is proposed for the decay phase, whereby an empirical irrotational and uniformly convergent horizontal velocity field interacting with an axially symmetric and height invariant magnetic field, reproduces the large-scale features of the much more complex convection observed inside sunspots.

astro-ph.SR↗
arXiv2012

Variation rate of sunspot area

The emergence of the magnetic field through the photosphere has multiple manifestations and sunspots are the most prominent examples of this. One of the most relevant sunspot properties, to study both its structure and evolution, is the sunspot area: either total, umbra or penumbra area. Recently Schlichenmaier et al. (2010) studied the evolution of the active region (AR) NOAA 11024 concluding that during the penumbra formation the umbra area remains constant and that the increase of the total sunspot area is caused exclusively by the penumbra growth. In this presentation the Schlichenmaier's conclusion is firstly tested, investigating the evolution of four different ARs. Hundreds of Intensitygram images from the Helioseismic and Magnetic Imager (HMI) images are used, obtained by the Solar Dynamics Observatory, in order to describe the area evolution of the above ARs and estimate the increase and decrease rates for umbra and penumbra areas, separately. A simple magnetohydrodynamic model is then tentatively used in a first approximation to explain the observed results.

astro-ph.SR↗
arXiv2012

Application of Neural Networks to the study of stellar model solutions

Artificial neural networks (ANN) have different applications in Astronomy, including data reduction and data mining. In this work we propose the use ANNs in the identification of stellar model solutions. We illustrate this method, by applying an ANN to the 0.8M$_\odot$ star CG Cyg B. Our ANN was trained using 60,000 different 0.8M$_\odot$ stellar models. With this approach we identify the models which reproduce CG Cyg B's position in the HR diagram. We observe a correlation between the model's initial metal and helium abundance which, in most cases, does not agree with a helium to metal enrichment ratio $Δ$Y/$Δ$Z=2. Moreover, we identify a correlation between the model's initial helium/metal abundance and both its age and mixing-length parameter. Additionally, every model found has a mixing-length parameter below 1.3. This means that CG Cyg B's mixing-length parameter is clearly smaller than the solar one. From this study we conclude that ANNs are well suited to deal with the degeneracy of model solutions of solar type stars.

astro-ph.SR↗
arXiv2010

Higher depletion of lithium in planet host stars: no age and mass effect

Recent observational work by Israelian et al. has shown that sun-like planet host stars in the temperature range 5700K < Teff < 5850K have lithium abundances that are significantly lower than those observed for "single" field stars. In this letter we use stellar evolutionary models to show that differences in stellar mass and age are not responsible for the observed correlation. This result, along with the finding of Israelian et al., strongly suggest that the observed lithium difference is likely linked to some process related to the formation and evolution of planetary systems.

astro-ph.SR↗
arXiv2009

A homogeneous spectroscopic analysis of host stars of transiting planets

The analysis of transiting extra-solar planets provides an enormous amount of information about the formation and evolution of planetary systems. A precise knowledge of the host stars is necessary to derive the planetary properties accurately. The properties of the host stars, especially their chemical composition, are also of interest in their own right. Information about planet formation is inferred by, among others, correlations between different parameters such as the orbital period and the metallicity of the host stars. The stellar properties studied should be derived as homogeneously as possible. The present work provides new, uniformly derived parameters for 13 host stars of transiting planets. Effective temperature, surface gravity, microturbulence parameter, and iron abundance were derived from spectra of both high signal-to-noise ratio and high resolution by assuming iron excitation and ionization equilibria. For some stars, the new parameters differ from previous determinations, which is indicative of changes in the planetary radii. A systematic offset in the abundance scale with respect to previous assessments is found for the TrES and HAT objects. Our abundance measurements are remarkably robust in terms of the uncertainties in surface gravities. The iron abundances measured in the present work are supplemented by all previous determinations using the same analysis technique. The distribution of iron abundance then agrees well with the known metal-rich distribution of planet host stars. To facilitate future studies, the spectroscopic results of the current work are supplemented by the findings for other host stars of transiting planets, for a total dataset of 50 objects.

astro-ph.SR↗
arXiv2008

Analysis of 70 Ophiuchi AB including seismic constraints

The analysis of solar-like oscillations for stars belonging to a binary system provides a unique opportunity to probe the internal stellar structure and to test our knowledge of stellar physics. Such oscillations have been recently observed and characterized for the A component of the 70 Ophiuchi system. A model of 70 Ophiuchi AB that correctly reproduces all observational constraints available for both stars is determined. An age of 6.2 +- 1.0 Gyr is found with an initial helium mass fraction Y_i=0.266 +- 0.015 and an initial metallicity (Z/X)_i=0.0300 +- 0.0025 when atomic diffusion is included and a solar value of the mixing-length parameter assumed. A precise and independent determination of the value of the mixing-length parameter needed to model 70 Oph A requires accurate measurement of the mean small separation, which is not available yet. Current asteroseismic observations, however, suggest that the value of the mixing-length parameter of 70 Oph A is lower or equal to the solar calibrated value. The effects of atomic diffusion and of the choice of the adopted solar mixture were also studied. We also tested and compared the theoretical tools used for the modeling of stars for which p-modes frequencies are detected by performing this analysis with three different stellar evolution codes and two different calibration methods. We found that the different evolution codes and calibration methods we used led to perfectly coherent results.

astro-ph↗
arXiv2006

On the effect of overshooting as predicted by the modelling of the pre-main sequence evolution of a 2 solar-mass star

We discuss the effects of convective overshooting in the PMS evolution of intermediate mass stars, by analysing in detail the early evolution towards the main sequence of a 2 M_sun stellar model. These effects can be extremely important in the end of the PMS, when the abundances in CNO elements approach the equilibrium in the centre. We provide a possible physical explanation on why a moderate amount of overshooting produces, as the star approaches the ZAMS, an extra loop in the evolutionary tracks on the HR diagram. An interesting feature is that there is a very well defined amount of overshooting (for a given stellar mass and chemical composition) beyond which a loop is produced. For smaller amounts of overshooting such a loop does not take place and the evolutionary tracks are similar to the ones obtained by Iben (1965). The amount of overshooting needed to produce the loop decreases with stellar mass. We discuss the underlining physical reasons for the behaviour predicted by the evolution models and argue that it provides a crucial observational test for convective overshooting in the core of intermediate mass stars.

astro-ph↗
arXiv2006

Report on the CoRoT Evolution and Seismic Tools Activity

We present the work undertaken by the Evolution and Seismic Tools Activity (ESTA) team of the CoRoT Seismology Working Group. We have focused on two main tasks: Task 1 - now finished - has aimed at testing, comparing and optimising seven stellar evolution codes which will be used to model the internal structure and evolution of the CoRoT target stars. Task 2, still underway, aims at testing, comparing and optimising different seismic codes used to calculate the oscillations of models for different types of stars. The results already obtained are quite satisfactory, showing minor differences between the different numerical tools provided the same assumptions on the physical parameters are made. This work gives us confidence on the numerical tools that will be available to interpret the future CoRoT seismic data.

astro-ph↗
arXiv2004

The role of the time step and overshooting in the modelling of PMS evolution: the case of EK Cephei

We have produced detailed evolutionary models of the binary EK Cep using the CESAM stellar evolution code (Morel 1997). A $χ^2$-minimisation was performed to derive the most reliable set of modelling parameters. We have found that an evolutionary age of about 26.8 Myrs fits both components in the same isochrone. The positions of EK Cep A and B in the HR diagram are consistent (within the observational uncertainties) with our results. Our revised calibration shows clearly that EK Cep is in the beginning of the main sequence, while EK Cep B is indeed a PMS star. Such a combination allows for a precise age determination of the binary, and provides a strict test of the modelling. In particular we have found that the definition of the time step in calculating the PMS evolution is crucial to reproduce the observations. A discussion of the optimal time step for calculating PMS evolution is presented. The fitting to the radii of both components is a more difficult task; although we managed to do it for EK Cep B, EK Cep A has a lower radius than our best models. We further studied the effect of the inclusion of a moderate convective overshooting; the calibration of the binary is not significantly altered, but the effect of the inclusion of overshooting can be dramatic in the approach to the main sequence of stars with masses high enough to burn hydrogen through the CNO cycle on the main sequence.

astro-ph↗
arXiv2003

Disentangling discrepancies between stellar evolution theory and sub-solar mass stars. The influence of the mixing length parameter for the UV Psc binary

Serious discrepancies have recently been observed between predictions of stellar evolution models in the 0.7-1.1 M_sun mass range and accurately measured properties of binary stars with components in this mass range. We study one of these objects, the eclipsing binary UV Piscium, which is particularly interesting because Popper (1997) derived age estimates for each component which differed by more than a factor of two. In an attempt to solve this significant discrepancy (a difference in age of 11 Gyr), we compute a large grid of stellar evolution models with the CESAM code for each component. By fixing the masses to their accurately determined values (relative error smaller than 1% for both stars), we consider a wide range of possible metallicities Z (0.01 to 0.05), and Helium content Y (0.25 to 0.34) uncorrelated to Z. In addition, the mixing length parameter alpha_MLT is left as another free parameter. We obtain a best fit in the T_eff-radius diagram for a common chemical composition (Z, Y)=(0.012, 0.31), but a different MLT parameter alpha_MLT_A = 0.95+-0.12(statistical)+0.30(systematic) and alpha_MLT_B = 0.65+-0.07(stat)+0.10(syst). The apparent age discrepancy found by Popper (1997) disappears with this solution, the components being coeval to within 1%. This suggests that fixing alpha_MLT to its solar value (~1.6), a common hypothesis assumed in most stellar evolutionary models, may not be correct. Secondly, since alpha_MLT is smaller for the less massive component, this suggests that the MLT parameter may decrease with stellar mass, showing yet another shortcoming of the mixing length theory to explain stellar convection. This trend needs further confirmation with other binary stars with accurate data.

astro-ph↗
arXiv2002

A revised HRD for individual components of binary systems from BaSeL BVRI synthetic photometry. Influence of interstellar extinction and stellar rotation

Johnson BVRI photometric data for individual components of binary systems have been provided by ten Brummelaar et al. (2000). This is essential because such binaries could play a critical role in calibrating the single-star stellar evolution theory. While they derived the effective temperature from their estimated spectral type, we infer metallicity-dependent Teffs from a minimizing method fitting the B-V, V-R and V-I colours. For this purpose, a grid of 621,600 flux distributions were computed from the Basel Stellar Library (BaSeL 2.2) of model-atmosphere spectra, and their theoretical colours compared with the observed photometry. As a matter of fact, the BaSeL colours show a very good agreement with the BVRI metallicity-dependent empirical calibrations of Alonso et al. (1996), temperatures being different by 3+-3 % in the range 4000-8000 K for dwarf stars. Before deriving the metallicity-dependent Teff from the BaSeL models, we paid particular attention to the influence of reddening and stellar rotation. A comparison between the MExcess code and neutral hydrogen column density data shows a good agreement for the sample but we point out a few directions where the MExcess model overestimates the E(B-V) colour excess. Influence of stellar rotation on the BVRI colours can be neglected except for 5 stars with large vsini, the maximum effect on temperature being less than 5%. Our final results are in good agreement with previous spectroscopic determinations available for a few primary components, and with ten Brummelaar et al. below ~10,000 K. Nevertheless, we obtain an increasing disagreement with their Teffs beyond 10,000 K. Finally, we provide a revised Hertzsprung-Russell diagram for the systems with the more accurately determined temperatures. (Abridged)

astro-ph↗