Acreció de matèria sobre nanes blanques

The long-term evolution of accreting carbon-oxygen white dwarfs in close binary sistems is considered. The mass of the star is M = 1.3 MO and the rate of accretion M = 10-10 MO •yr-1. The effects of solidification of the star's interior are studied by considering three different cases of chemical separation, associated with different cooling times. The results show that diverse outcomes are possible, ranging from total collapse for maximum separation to off-center ignition for partial chemical differentiation

Data-driven identification of optimal substitutions in soccer

L'anàlisi basada en dades del futbol és un camp en auge, i els clubs dediquen cada vegada més recursos a obtenir un avantatge competitiu mitjançant tècniques basades en dades. Les substitucions són la principal eina de la qual disposa un entrenador per a intervenir en el transcurs del joc, i la seva limitació i rellevància han despertat l'interès pel seu estudi. En aquesta tesi busquem un enfocament analític per a la identificació i predicció de substitucions òptimes. Amb el recent canvi en la legislació futbolística, ara es permeten a cada equip fins a cinc substitucions per partit. Comparem el nou paradigma amb l'anterior i busquem les substitucions òptimes amb l'ús de models basats en dades. Amb classificadors d'aprenentatge automàtic i un model de probabilitat de victòria en directe sensible a les substitucions, s'han avaluat els canvis de jugadors. Els mateixos models s'han utilitzat per a simular substitucions de diferent tipus i en moments alternatius, amb la finalitat de realitzar plantejaments basats en dades que augmentin les probabilitats d'èxit. L'addició de canvis addicionals ha provocat un augment de les intervencions tàctiques dels entrenadors, però la dinàmica del partit es manté igual. Els models d'aprenentatge automàtic obtenen bons resultats en la predicció de la valoració de les substitucions. El model de probabilitat de victòria és sensible a les substitucions, que solen tenir un millor efecte per a l'equip que les realitza. Les substitucions ofensives solen augmentar les probabilitats de victòria, especialment per als equips que van perdent. No s'observa que cap moment sigui significativament millor per a fer el canvi, però en casos particulars pot ser rellevant.El análisis basado en datos del fútbol es un campo en auge, y los clubes dedican cada vez más recursos a obtener una ventaja competitiva mediante técnicas basadas en datos. Las sustituciones son la principal herramienta de la que dispone un entrenador para intervenir en el transcurso del juego, y su limitación y relevancia han despertado el interés por su estudio. En esta tesis buscamos un enfoque analítico para la identificación y predicción de sustituciones óptimas. Con el reciente cambio en la legislación futbolística, ahora se permiten a cada equipo hasta cinco sustituciones por partido. Comparamos el nuevo paradigma con el anterior y buscamos las sustituciones óptimas con el uso de modelos basados en datos. Con clasificadores de aprendizaje automático y un modelo de probabilidad de victoria en directo sensible a las sustituciones, se han evaluado los cambios de jugadores. Los mismos modelos se han utilizado para simular sustituciones de distinto tipo y en momentos alternativos, con el fin de realizar planteamientos basados en datos que aumenten las probabilidades de éxito. La adición de cambios adicionales ha provocado un aumento de las intervenciones tácticas de los entrenadores, pero la dinámica del partido se mantiene igual. Los modelos de aprendizaje automático obtienen buenos resultados en la predicción de la valoración de las sustituciones. El modelo de probabilidad de victoria es sensible a las sustituciones, que suelen tener un mejor efecto para el equipo que las realiza. Las sustituciones ofensivas suelen aumentar las probabilidades de victoria, especialmente para los equipos que van perdiendo. No se observa que ningún momento sea significativamente mejor para hacer el cambio, pero en casos particulares puede ser relevante.Data-driven football analytics is a rising field, and clubs are spending more and more resources on gaining a competitive edge through data-driven techniques. Substitutions are the main tool a coach has to intervene in the course of the game, and their limitation and relevance have attracted interest to their study. In this thesis, we seek a data-informed approach to identifying and predicting optimal substitutions. With the recent change in football legislation, now each team is permitted up to five substitutions per match. We compare the new paradigm with the prior one and look for optimal substitutions with the use of data-based models. With machine learning classifiers and a substitution sensible in-game win probability model, player changes have been assessed. The same models have been used for simulating alternative types of substitution and timing, in order to make data-driven approaches that increase the chances of success. The addition of extra substitutions has resulted in an increase in tactical interventions by coaches, but the match dynamics have remained the same. Machine learning models obtain good results in the prediction of substitution assessment. The win probability model is sensible to substitutions, which have generally a better effect on the substituting team. Offensive substitutions generally increase the winning probabilities, especially for losing teams. No timing is observed to be significantly better for doing substitutions, but in particular cases can be very relevant.Outgoin

A remarkable recurrent nova in M 31: The predicted 2014 outburst in X-rays with Swift

The M 31 nova M31N 2008-12a was recently found to be a recurrent nova (RN) with a recurrence time of about 1 year. This is by far the fastest recurrence time scale of any known RNe. Our optical monitoring programme detected the predicted 2014 outburst of M31N 2008-12a in early October. We immediately initiated an X-ray/UV monitoring campaign with Swift to study the multiwavelength evolution of the outburst. We monitored M31N 2008-12a with daily Swift observations for 20 days after discovery, covering the entire supersoft X-ray source (SSS) phase. We detected SSS emission around day six after outburst. The SSS state lasted for approximately two weeks until about day 19. M31N 2008-12a was a bright X-ray source with a high blackbody temperature. The X-ray properties of this outburst were very similar to the 2013 eruption. Combined X-ray spectra show a fast rise and decline of the effective blackbody temperature. The short-term X-ray light curve showed strong, aperiodic variability which decreased significantly after about day 14. Overall, the X-ray properties of M31N 2008-12a are consistent with the average population properties of M 31 novae. The optical and X-ray light curves can be scaled uniformly to show similar time scales as those of the Galactic RNe U Sco or RS Oph. The SSS evolution time scales and effective temperatures are consistent with a high-mass WD. We predict the next outburst of M31N 2008-12a to occur in autumn 2015.Comment: 13 pages, 7 figures, 3 tables; accepted for publication in A&

The cooling of CO white dwarfs: influence of the internal chemical distribution

In this paper we compute detailed evolutionary models providing chemical profiles for white dwarfs having progenitors in the mass range from 1.0 to 7 M_{\sun} and we examine the influence of such profiles in the cooling process. The influence of the process of separation of carbon and oxygen during crystallization is decreased as a consequence of the initial stratification, but it is still important and cannot be neglected. As an example, the best fit to the luminosity functions of Liebert et al. (1988) and Oswalt et al. (1996) gives and age of the disk of 9.3 and 11.0 Gyr, respectively, when this effect is taken into account, and only 8.3 and 10.0 Gyrs when it is neglected.Comment: Accepted for publication in ApJ (26 pages, 7 figures, aasms4

Simulations of the X-ray imaging capabilities of the Silicon Drift Detectors (SDD) for the LOFT Wide Field Monitor

The Large Observatory For X-ray Timing (LOFT), selected by ESA as one of the four Cosmic Vision M3 candidate missions to undergo an assessment phase, will revolutionize the study of compact objects in our galaxy and of the brightest supermassive black holes in active galactic nuclei. The Large Area Detector (LAD), carrying an unprecedented effective area of 10 m^2, is complemented by a coded-mask Wide Field Monitor, in charge of monitoring a large fraction of the sky potentially accessible to the LAD, to provide the history and context for the sources observed by LAD and to trigger its observations on their most interesting and extreme states. In this paper we present detailed simulations of the imaging capabilities of the Silicon Drift Detectors developed for the LOFT Wide Field Monitor detection plane. The simulations explore a large parameter space for both the detector design and the environmental conditions, allowing us to optimize the detector characteristics and demonstrating the X-ray imaging performance of the large-area SDDs in the 2-50 keV energy band.Comment: Proceedings of SPIE, Vol. 8443, Paper No. 8443-210, 201

Observations of SN2011fe with INTEGRAL

SN2011fe was detected by the Palomar Transient Factory on August 24th 2011 in M101 few hours after the explosion. From the early spectra it was immediately realized that it was a Type Ia supernova thus making this event the brightest one discovered in the last twenty years. In this paper the observations performed with the instruments on board of INTEGRAL (SPI, IBIS/ISGRI, JEM-X and OMC) before and after the maximum of the optical light as well as the interpretation in terms of the existing models of $\gamma$--ray emission from such kind of supernovae are reported. All INTEGRAL high-energy have only been able to provide upper limits to the expected emission due to the decay of $^{56}$Ni. These bounds allow to reject explosions involving a massive white dwarf in the sub--Chandrasekhar scenario. On the other hand, the optical light curve obtained with the OMC camera suggests that the event was produced by a delayed detonation of a CO white dwarf that produced $\sim 0.5$ M$\odot$ of $^{56}$Ni. In this particular case, INTEGRAL would have only been able to detect the early $\gamma$--ray emission if the supernova had occurred at a distance of 2 -3 Mpc, although the brightest event could be visible up to distances larger by a factor two.Comment: Proceedings of "An INTEGRAL view of the high-energy sky (the first 10 years)" the 9th INTEGRAL Workshop, October 15-19, 2012, Paris, France, in Proceedings of Science (INTEGRAL 2012), Eds. A. Goldwurm, F. Lebrun and C. Winkler, http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=176, id number PoS (INTEGRAL 2012) 103 (2013

Observation of SN2011fe with INTEGRAL. I. Pre--maximum phase

SN2011fe was detected by the Palomar Transient Factory on August 24th 2011 in M101 a few hours after the explosion. From the early optical spectra it was immediately realized that it was a Type Ia supernova thus making this event the brightest one discovered in the last twenty years. The distance of the event offered the rare opportunity to perform a detailed observation with the instruments on board of INTEGRAL to detect the gamma-ray emission expected from the decay chains of $^{56}$Ni. The observations were performed in two runs, one before and around the optical maximum, aimed to detect the early emission from the decay of $^{56}$Ni and another after this maximum aimed to detect the emission of $^{56}$Co. The observations performed with the instruments on board of INTEGRAL (SPI, IBIS/ISGRI, JEMX and OMC) have been analyzed and compared with the existing models of gamma-ray emission from such kind of supernovae. In this paper, the analysis of the gamma-ray emission has been restricted to the first epoch. Both, SPI and IBIS/ISGRI, only provide upper-limits to the expected emission due to the decay of $^{56}$Ni. These upper-limits on the gamma-ray flux are of 7.1 $\times$ 10$^{-5}$ ph/s/cm$^2$ for the 158 keV line and of 2.3 $\times$ 10$^{-4}$ ph/s/cm$^2$ for the 812 keV line. These bounds allow to reject at the $2\sigma$ level explosions involving a massive white dwarf, $\sim 1$ M$\odot$ in the sub--Chandrasekhar scenario and specifically all models that would have substantial amounts of radioactive $^{56}$Ni in the outer layers of the exploding star responsible of the SN2011fe event. The optical light curve obtained with the OMC camera also suggests that SN2011fe was the outcome of the explosion, possibly a delayed detonation although other models are possible, of a CO white dwarf that synthesized $\sim 0.55$ M$_\odot$ of $^{56}$Ni. For this specific model.Comment: Accepted for publication in A&A. 10 pages, 10 figure

The Possible White Dwarf-Neutron Star Connection

The current status of the problem of whether neutron stars can form, in close binary systems, by accretion-induced collapse (AIC) of white dwarfs is examined. We find that, in principle, both initially cold C+O white dwarfs in the high-mass tail of their mass distribution in binaries and O+Ne+Mg white dwarfs can produce neutron stars. Which fractions of neutron stars in different types of binaries (or descendants from binaries) might originate from this process remains uncertain.Comment: 6 pages. To appear in "White Dwarfs", ed. J. Isern, M. Hernanz, and E. Garcia-Berro (Dordrecht: Kluwer