Factors subjectius de la construcció sostenible.

El concepte de sostenibilitat requereix del concepte de societat sostenible. Quan ens referim a la sostenibilitat d'un sistema, ens referim a la d'un sistema humà, amb els seus aspectes materials i culturals, i que ha sofert (o ha arribat a) un desplaçament respecte de l'estat natural. La conservació d’aquest desplaçament és el que ens preocupa. Quan considerem la sostenibilitat en l'ambient construït, aquestes dues categories material i cultural prenen la forma d'un debat que s'ha vingut donant al llarg de tota la modernitat, en el qual els rols d'arquitecte i enginyer s'oposen i completen. Al primer li correspondrien les qüestions de disseny, estil, història, aspectes culturals en general; al segon, les qüestions de càlcul, construcció, manteniment, aspectes materials en general. Durant aquest debat, la postura predominant ha anat alternant d’un costat a l’altre i, la majoria de vegades, s'ha produït una escissió on les solucions arquitectòniques i d’enginyeria més que complementar-se s’han superposat. Com explica McCleary respecte de l'enginyer estructuralista: “L'origen del cisma és clar: Per a l'arquitecte, el disseny comença per considerar la humanització de l'espai – la preocupació principal és habitar; per a l'enginyer, el disseny comença per respondre a les propietats dels materials i a la lògica de la mecànica estructural – el focus és a l'estructuració” . En segon lloc, és necessari considerar l'arquitectura com un fenomen social en les seves causes i efectes. El fet que els edificis conformin l'espai continent on es desenvolupen la majoria de les activitats humanes, els atorga la seva importància com factor de conformació i, alhora, expressió d'una societat. L'ambient construït no és únicament un suport físic, sinó que a més involucra la interacció entre aquest i els seus ocupants. Aquestes consideracions preliminars serveixen per a emmarcar les dimensions del problema i alhora per a ordenar l'anàlisi subsegüent.El concepto de sostenibilidad requiere del concepto de sociedad sostenible. Cuando nos referimos a la sostenibilidad de un sistema, nos referimos a la de un sistema humano, con sus aspectos materiales y culturales, y que ha sufrido (o alcanzado) un desplazamiento respecto del estado natural. Es la conservación de este desplazamiento lo que nos preocupa. Al considerar la sostenibilidad en el ambiente construido, estas dos categorías de lo material y lo cultural toman la forma de un debate que se ha venido dando a lo largo de toda la modernidad, en el que los roles de arquitecto e ingeniero se oponen y complementan. Al primero le corresponderían las cuestiones de diseño, estilo, historia, aspectos culturales en general; al segundo, las cuestiones de cálculo, construcción, mantenimiento, aspectos materiales en general. Durante este debate, la postura predominante ha ido alternando de lado, y la mayor parte de las veces se ha producido una escisión donde las soluciones arquitectónicas e ingenieriles se superponen más de lo que se complementan. Como explica McCleary respecto del ingeniero estructuralista: “El origen del cisma es claro: para el arquitecto, el diseño comienza por considerar la humanización del espacio – la preocupación principal es el habitar; para el ingeniero, el diseño comienza por responder a las propiedades de los materiales y a la lógica de la mecánica estructural – el foco es en la estructuración”. En segundo lugar es necesario considerar a la arquitectura como fenómeno social en sus causas y efectos. El hecho de que los edificios conformen el espacio continente donde se desarrolla la mayoría de las actividades humanas les otorga su importancia como factor de conformación, y a la vez expresión de una sociedad. El ambiente construido no es solamente un soporte físico, sino que además involucra la interacción entre éste y sus ocupantes. Estas consideraciones preliminares sirven para enmarcar las dimensiones del problema y a la vez para ordenar el análisis subsiguiente

Gaia 0007-1605: an old triple system with an inner brown dwarf-white dwarf binary and an outer white dwarf companion

We identify Gaia 0007–1605 A,C as the first inner brown dwarf–white dwarf binary of a hierarchical triple system in which the outer component is another white dwarf (Gaia 0007–1605 B). From optical/near-infrared spectroscopy obtained at the Very Large Telescope with the X-Shooter instrument and/or from Gaia photometry plus spectral energy distribution fitting, we determine the effective temperatures and masses of the two white dwarfs (12,018 ± 68 K and 0.54 ± 0.01 M¿ for Gaia 0007–1605 A and 4445 ± 116 K and 0.56 ± 0.05 M¿ for Gaia 0007–1605 B) and the effective temperature of the brown dwarf (1850 ± 50 K; corresponding to spectral type L3 ± 1). By analyzing the available TESS light curves of Gaia 0007–1605 A,C we detect a signal at 1.0446 ± 0.0015 days with an amplitude of 6.25 ppt, which we interpret as the orbital period modulated from irradiation effects of the white dwarf on the brown dwarf's surface. This drives us to speculate that the inner binary evolved through a common-envelope phase in the past. Using the outer white dwarf as a cosmochronometer and analyzing the kinematic properties of the system, we conclude that the triple system is about 10 Gyr old.Postprint (published version

The star formation history of Gaia white dwarf population through its colour-magnitude diagram

White dwarfs are the most common stellar remnants. Furthermore, as being old objects, their study could shed new light on different questions related to the history, formation and evolution of the Galaxy. Despite these objects have been broadly studied from a theoretical point of view, the observational data has been limited to a poor statistical sample, due to the intrinsic low luminosity of white dwarfs. However, thanks to the recent Gaia EDR3, for the first time, a significant sample of the White dwarf population of our Galaxy, containing around 13,000 objects up to 100 pc from the Sun, has been obtained. Such data, in particular its color-magnitude diagram, provides the ideal scenario for extracting the maximum information. This communication reports a work-in-progress of a widely applied technique for recovering the star formation history of galaxies through its color-magnitude diagram applied, in this case, for first time to the local White dwarf population.Peer ReviewedPostprint (published version

The white dwarf luminosity function II. The efect of the measurement errors and other biases

The disc white dwarf luminosity function is an important tool for studying the solar neighbourhood, since it allows the determination of several Galactic parameters, the most important one being the age of the Galactic disc. However, only the 1/Vmax method has been employed so far for observationally determining the white dwarf luminosity function, whereas for other kind of luminosity functions several other methods have been frequently used. Moreover, the procedures to determine the white dwarf luminosity function are not free of biases. These biases have two different origins: they can either be of statistical nature or a consequence of the measurement errors. In a previous paper we carried out an in-depth study of the first category of biases for several luminosity function estimators. In this paper we focus on the biases introduced by the measurement errors and on the effects of the degree of contamination of the input sample used to build the disc white dwarf luminosity function by different kinematical populations. To assess the extent of these biases we use a Monte Carlo simulator to generate a controlled synthetic population and analyse the behaviour of the disc white dwarf luminosity function for several assumptions about the magnitude of the measurement errors and for several degrees of contamination, comparing the performances of the most robust luminosity function estimators under such conditions.Peer Reviewe

The white dwarf population of tri-axial haloes

The nature of the several microlensing events observed by the MACHO team towards the Large Magellanic Cloud (LMC) is still a controversial subject. Substellar objects and stars with masses larger than ~ 1M¿ have been ruled out as major components of a Massive Astrophysical Halo Object (MACHO) Galactic halo. Stars of near half-solar mass, in particular white dwarfs, appear to be the best candidates to explain the observed microlensing events. On the other hand, observational evidence based on the structure of the debris of the Sagittarius dwarf galaxy suggest that the Galactic halo is non-spherical. We use a tri-axial halo model and advanced Monte Carlo techniques to study the contribution of the halo white dwarf population to the dark matter content of the GalaxyPeer ReviewedPostprint (author’s final draft

The population of single and binary white dwarfs of the Galactic bulge

Recent Hubble Space Telescope observations have unveiled the white dwarf cooling sequence of the Galactic bulge. Although the degenerate sequence can be well fitted employing the most up-to-date theoretical cooling sequences, observations show a systematic excess of red objects that cannot be explained by the theoretical models of single carbon–oxygen white dwarfs of the appropriate masses. Here, we present a population synthesis study of the white dwarf cooling sequence of the Galactic bulge that takes into account the populations of both single white dwarfs and binary systems containing at least one white dwarf. These calculations incorporate state-of-the-art cooling sequences for white dwarfs with hydrogen-rich and hydrogen-deficient atmospheres, for both white dwarfs with carbon–oxygen and helium cores, and also take into account detailed prescriptions of the evolutionary history of binary systems. Our Monte Carlo simulator also incorporates all the known observational biases. This allows us to model with a high degree of realism the white dwarf population of the Galactic bulge. We find that the observed excess of red stars can be partially attributed to white dwarf plus main sequence binaries, and to cataclysmic variables or dwarf novae. Our best fit is obtained with a higher binary fraction and an initial mass function slope steeper than standard values, as well as with the inclusion of differential reddening and blending. Our results also show that the possible contribution of double degenerate systems or young and thick-discbulge stars is negligible.Peer ReviewedPostprint (published version

A population synthesis study of the luminosity function of hot white dwarfs

Context. We present a coherent and detailed Monte Carlo simulation of the population of hot white dwarfs. We assess the statistical significance of the hot end of the white dwarf luminosity function and the role played by the bolometric corrections of hydrogen-rich white dwarfs at high effective temperatures. Aims. We use the most up-to-date stellar evolutionary models and implement a full description of the observational selection biases to obtain realistic simulations of the observed white dwarf population. Methods. Our theoretical results are compared with the luminosity function of hot white dwarfs obtained from the Sloan Digital Sky Survey (SDSS), for both DA and non-DA white dwarfs. Results. We find that the theoretical results are in excellent agreement with the observational data for the population of white dwarfs with hydrogen deficient atmospheres (non-DA white dwarfs). For the population of white dwarfs with hydrogen-rich atmospheres (white dwarfs of the DA class), our simulations show some discrepancies with the observations for the brightest luminosity bins, namely those corresponding to luminosities larger than ~10 L.These discrepancies can be attributed to the way in which the masses of the white dwarfs contributing to this luminosity bin have been computed, as most of them have masses smaller than the theoretical lower limit for carbon-oxygen white dwarfs. Conclusions. We conclude that the way in which the observational luminosity function of hot white dwarfs is obtained is very sensitive to the particular implementation of the method used to derive the masses of the sample. We also provide a revised luminosity function for hot white dwarfs with hydrogen-rich atmospheres. © ESO, 2014.Peer ReviewedPostprint (published version

The population of white dwarf-main sequence binaries in the SDSS DR 12

We present a Monte Carlo population synthesis study of white dwarf-main sequence (WD+MS) binaries in the Galactic disc aimed at reproducing the ensemble properties of the entire population observed by the Sloan Digital Sky Survey (SDSS) Data Release 12. Our simulations take into account all known observational biases and use the most up-to-date stellar evolutionary models. This allows us to perform a sound comparison between the simulations and the observational data. We find that the properties of the simulated and observed parameter distributions agree best when assuming low values of the common envelope efficiency (0.2-0.3), a result that is in agreement with previous findings obtained by observational and population synthesis studies of close SDSSWD+MS binaries.We also show that all synthetic populations that result from adopting an initial mass ratio distribution with a positive slope are excluded by observations. Finally, we confirm that the properties of the simulated WD+MS binary populations are nearly independent of the age adopted for the thin disc, on the contribution of WD+MS binaries from the thick disc (0-17 per cent of the total population) and on the assumed fraction of the internal energy that is used to eject the envelope during the common envelope phase (0.1-0.5).Peer ReviewedPostprint (published version