CD Tau: a detached eclipsing binary with a solar-mass companion

We present a detailed analysis of the detached eclipsing binary CD Tau. A large variety of observational data, in form of IR photometry, CORAVEL radial velocity observations and high-resolution spectra, are combined with the published light curves to derive accurate absolute dimensions and effective temperature of the components, as well as the metal abundance of the system. We obtain: MA=1.442(16) Mo, RA=1.798(17) Ro, TeffA=6200(50) K, MB=1.368(16) Msun, RB=1.584(20) Run and TeffB=6200(50) K. The metal content of the system is determined to be [Fe/H]=+0.08(15) dex. In addition, the eclipsing binary has a K-type close visual companion at about 10-arcsec separation, which is shown to be physically linked, thus sharing a common origin. The effective temperature of the visual companion (Teff=5250(200) K) is determined from synthetic spectrum fitting, and its luminosity (log L/Lo=-0.27(6)), and therefore its radius (R=0.89(9) Ro), are obtained from comparison with the apparent magnitude of the eclipsing pair. The observed fundamental properties of the eclipsing components are compared with the predictions of evolutionary models, and we obtain good agreement for an age of 2.6 Gyr and a chemical composition of Z=0.026 and Y=0.26. Furthermore, we test the evolutionary models for solar-mass stars and we conclude that the physical properties of the visual companion are very accurately described by the same isochrone that fits the more massive components.Comment: 9 pages, 6 figures, accepted for publication in MNRA

2009, l'Any Internacional de l'Astronomia

La Unió Astronòmica Internacional va promoure el 2009 com l'Any Internacional de l'Astronomia (AIA-IYA2009) sota el lema, ≪Un Univers per descobrir≫. L'AIA-IYA2009 celebra les primeres observacions astronòmiques amb telescopi que Galileu Galilei va fer el 1609, i que van ser l'inici de 400 anys seguits de descobriments que encara continuen. L'Any Internacional de l'Astronomia ha de ser una celebració global de l'astronomia fent èmfasi en la divulgació per al públic en general, en l'educació a tots els nivells i en la transmissió de la recerca puntera que s'està a duent a terme. Amb l'organització d'activitats en els àmbits local, autonòmic, estatal i internacional durant tot el 2009, l'AIA-IYA2009 vol contribuir a transmetre a la societat el coneixement actual de l'Univers i que cadascú pugui descobrir-lo per si mateix

Spectrophotometric calibration of low-resolution spectra

Low-resolution spectroscopy is a frequently used technique. Aperture prism spectroscopy in particular is an important tool for large-scale survey observations. The ongoing ESA space mission Gaia is the currently most relevant example. In this work we analyse the fundamental limitations of the calibration of low-resolution spectrophotometric observations and introduce a calibration method that avoids simplifying assumptions on the smearing effects of the line spread functions. To this aim, we developed a functional analytic mathematical formulation of the problem of spectrophotometric calibration. In this formulation, the calibration process can be described as a linear mapping between two suitably constructed Hilbert spaces, independently of the resolution of the spectrophotometric instrument. The presented calibration method can provide a formally unusual but precise calibration of low-resolution spectrophotometry with non-negligible widths of line spread functions. We used the Gaia spectrophotometric instruments to demonstrate that the calibration method of this work can potentially provide a significantly better calibration than methods neglecting the smearing effects of the line spread functions.Comment: Final versio

The European Space Agency Gaia mission: exploring the Galaxy

La missió astromètrica Gaia és una de les dues properes missions punteres del programa científic de l'Agència Espacial Europea. Es va aprovar l'any 2000 i el llançament està previst per a l'agost del 2012. Gaia escombrarà el cel contínuament durant cinc anys, cosa que proporcionarà mesures de posicions i velocitats amb les precisions necessàries per a produir un cens estereoscòpic i cinemàtic d'aproximadament mil milions d'estrelles de tota la nostra galàxia i de més enllà; o sigui, aproximadament un 1 % de la població estel·lar galàctica. El principal objectiu científic de Gaia és quantificar la formació estel·lar en les primeres etapes i la subsegüent evolució dinàmica, química i de formació estel·lar en la nostra galàxia. Respondrà preguntes, com ara quan es van formar les estrelles a la Via Làctia, quan i com s'ha format la galàxia, i quina és la seva distribució de matèria fosca. La completesa de les observacions és fins a V = 20 mag, amb una precisió d'aproximadament 20 µ as a magnitud 15. La informació astromètrica es complementa amb informació astrofísica, obtinguda a bord mitjançant espectrofotometria i espectroscòpia, fet que permetrà derivar la composició química i l'edat de les estrelles. A més, Gaia observarà desenes de milers de sistemes planetaris extrasolars, uns 105 - 106 cossos menors del nostre sistema solar, milions de galàxies a l'Univers proper, i 500.000 quàsars llunyans. Proporcionarà un seguit de nous testos estrictes a la relativitat general i la cosmologia. L'estimació és que, una vegada processades les dades adquirides per Gaia, el volum total de dades serà del voltant d'un petabyte. El repte del processament de dades és l'estreta relació que hi ha entre la informació astromètrica i l'astrofísica, que implica una solució global que millora la determinació dels paràmetres dels instruments, l'actitud del satèl·lit i les propietats dels objectes observats de manera iterativa. El Consorci per al Processament i l'Anàlisi de Dades és la col·laboració europea responsable de la preparació i l'execució del processament de dades.The Gaia astrometric mission is one of the next two cornerstones of the European Space Agency's science program. It was approved in 2000 and the launch is foreseen by August 2012. Gaia will continuously scan the entire sky for five years, yielding positional and velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars throughout our Galaxy and beyond, i.e., about 1% of the galactic stellar population. Gaia's main scientific goal is to quantify early formation and the subsequent dynamic and chemical evolution of the Milky Way and its history of star formation. It will provide insight into questions such as: When did the stars in our Galaxy form? When and how was it assembled? What is the distribution of dark matter? The stellar survey will have a completeness to V = 20 mag, with an accuracy of about 20 µas at 15 mag. The astrometric information will be combined with astrophysical data acquired through on-board spectrophotometry and spectroscopy, allowing the chemical composition and age of the stars to be derived. In addition, Gaia will observe tens of thousands of extra-solar planetary systems, some 105–106 minor bodies in our solar system, millions of galaxies in the nearby universe, and some 500,000 distant quasars. It will also provide a number of stringent new tests of general relativity and cosmology. Data acquired and processed as a result of the Gaia mission are estimated to amount to about 1 petabyte. The challenging problem is the close relationship between astrometric and astrophysical data, which involves a global iterative solution that updates instruments parameters, the attitude of the satellite, and the properties of the observed objects. The Data Processing and Analysis Consortium is a joint European effort in charge of preparation and execution of data processing

ECOLOGV AT AN INFORMAL LEARNING

During 1986 and 1 987, an itinerant exhibition on "Ecology" written by Professor Margalef was followed in eight cities in Catalonia, (NE Spain). An extensive survey was carried out that included a survey on visitors' opinions and an experimental study on learning. This paper studies the relationships between opinions on the different environments of the exhibition (in terms of "Like", "Dislike" and "Surprise"), the physical and formal contents of the environments, and the time spent by visitors in front of each. We also analyse the results of an experiment on learning applied to students from four different age levels who used the exhibition as a complement to their formal studies. The experiment evaluated the most liked and the most disliked topics in the exhibition. The factors studied which could have sorne effect on marks obtained in an examination were: a) seeing the exhibition; b) having prepared something on ecology at school before visiting the exhibition; c) receiving a general introduction on how to look at an exhibition, just before the visit. The frequency of positive opinions on a given environment is inversely related to its density of information and directly related to the time spent looking at it. Students using the exhibition as a complement to their formal education only benefit if they like the exhibition (studied environment by environment). Having prepared something on ecology at school before visiting the exhibition has striking effects on teacher trainees, which raises serious questions about the way formal teaching is often carried out