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Nomenclatura Unesco > (21) Astronomía y Astrofísica
(2101) Cosmología y cosmogonía (2102) Medio interplanetario
(2103) Astronomía optica (2104) Planetología
(2105) Radioastronomía (2106) Sistema solar
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Mostrando recursos 1 - 20 de 600

1. The white dwarf population of tri-axial haloes - Torres Gil, Santiago; Camacho Díaz, Judit; García-Berro Montilla, Enrique
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...

2. Monte Carlo simulations of post-common-envelope white dwarf + main sequence binaries: The effects of including recombination energy - Zorotovic, Monica; García-Berro Montilla, Enrique; Schreiber, Mathias R.; Camacho Díaz, Judit; Torres Gil, Santiago; Rebassa Mansergas, Alberto; Gänsicke, Boris T.
Context. Detached white dwarf + main sequence (WD+MS) post-common-envelope binaries (PCEBs) are perhaps the most suitable objects for testing predictions of close-compact binary-star evolution theories, in particular, common-envelope (CE) evolution. Consequently, the population of WD+MS PCEBs has been simulated by several authors in the past and the predictions have been compared with the observations. However, most of those theoretical predictions did not take into account the possible contributions to the envelope ejection from additional sources of energy (mostly recombination energy) stored in the envelope. Aims. Here we update existing binary population models of WD+MS PCEBs by assuming that in addition to...

3. On the origin of high-field magnetic white dwarfs - García-Berro Montilla, Enrique; Torres Gil, Santiago; Loren Aguilar, Pablo; Aznar Siguan, Gabriela; Camacho Díaz, Judit; Kulebi, Baybar; Isern Vilaboy, Jordi; Althaus, Leandro Gabriel; Corsico, Alejandro H.
Every two years, white dwarf researchers and enthusiasts meet to exchange their knowledge and discuss recent developments in white dwarf theory and observations. These proceedings are from the 18th European White Dwarf Workshop held at Pedagogical University of Cracow (Krakow, Poland) on 13th - 17th August, 2012. The scientific topics discussed in this Workshop included: pulsating white dwarfs; luminosity function, mass distribution, and populations; white dwarf structure and evolution; white dwarf catalogs and surveys; central stars of planetary nebulae; supernova progenitors; white dwarfs in novae and cataclysmic variables; white dwarfs in detached binaries; physical processes in white dwarfs and magnetic...

4. Double degenerate mergers as progenitors of high-field magnetic white dwarfs - García-Berro Montilla, Enrique; Lorén Aguilar, Pablo; Aznar Siguan, Gabriela; Torres Gil, Santiago; Camacho Díaz, Judit; Althaus, Leandro Gabriel; Córsico, Alejando Hugo; Kulebi, Baybar; Isern Vilaboy, Jordi
High-field magnetic white dwarfs have been long suspected to be the result of stellar mergers. However, the nature of the coalescing stars and the precise mech anism that produces the magnetic field are still unknown. Here we show that the hot, convective, diffe rentially rotating corona present in the outer layers of the remnant of the merger of two degenerate cores is able to produce magnetic fields of the required strength that do not decay for long timescales. We also show, using an state-of-the-art Monte Carlo simulator, that the expected number of high-field magn etic white dwarfs produced in this way is consistent with that found in the Solar neighborhood.

5. Monte Carlo simulations of post-common-envelope white dwarf plus main sequence binaries: comparison with the SDSS DR7 observed sample - Camacho Díaz, Judit; Torres Gil, Santiago; García-Berro Montilla, Enrique; Zorotovic, Monica; Schreiber, Mathias R.; Rebassa-Mansergas, Alberto; Nebot Gómez-Moran, Ada; Gänsicke, Boris T.
Context. Detached white dwarf + main sequence (WD+MS) systems represent the simplest population of post-common envelope binaries (PCEBs). Since the ensemble properties of this population carries important information about the characteristics of the common-envelope (CE) phase, it deserves close scrutiny. However, most population synthesis studies do not fully consider the effects of the observational selection biases of the samples used to compare with the theoretical simulations.; Aims. Here we present the results of a set of detailed Monte Carlo simulations of the population of WD+MS binaries in the Sloan Digital Sky Survey (SDSS) Data Release 7.; Methods. We used up-to-date...

6. White dwarfs with hydrogen-deficient atmospheres and the dark matter content of the Galaxy - Torres Gil, Santiago; Camacho Díaz, Judit; Isern Vilaboy, Jordi; García-Berro Montilla, Enrique
Peer Reviewed

7. Observational and Numerical Simulation Study of a Sequence of Eight Atmospheric Density Currents in Northern Spain - Soler Duffour, Maria Rosa; Udina, Mireia; Ferreres Soler, Enriqueta
A sequence of eight atmospheric density current fronts occurred in consecutive days are identified and analyzed using micrometeorological time series and numerical simulations. Observations were collected in the context of the INTERCLE project, which took place from September 2002 to November 2003 at the CIBA (Research Centre for the Lower Atmosphere) site located over the northern Spanish plateau. Numerical simulations used the Weather Research and Forecast (WRF) model with fine horizontal resolution (1 km). Both observations and simulations agree that the arrival of the density currents are characterized by a sharp change in temperature, wind velocity, wind direction and specific...

8. Cobalt-56 gamma-ray emission lines from the type Ia supernova 2014J - Churazov, Eugene; Sunyaev, Rashid; Isern Vilaboy, Jordi; Knodlseder, Jurgen; Jean, Pierre; Lebrun, François; Chugai, Nikolai; Grebenev, Sergei; Bravo Guil, Eduardo; Sazonov, Sergei; Renaud, Matthieu
A type Ia supernova is thought to be a thermonuclear explosion of either a single carbon–oxygen white dwarf or a pair of merging white dwarfs. The explosion fuses a large amount of radioactive 56Ni. After the explosion, the decay chain from 56Ni to 56Co to 56Fe generates ¿-ray photons, which are reprocessed in the expanding ejecta and give rise to powerful optical emission. Here we report the detection of 56Co lines at energies of 847 and 1,238 kiloelectronvolts and a ¿-ray continuum in the 200–400 kiloelectronvolt band from the type Ia supernova 2014J in the nearby galaxy M82. The line...

9. Cobalt-56 gamma-ray emission lines from the type Ia supernova 2014J - Churazov, Eugene; Sunyaev, Rashid; Isern Vilaboy, Jordi; Knodlseder, Jurgen; Jean, Pierre; Lebrun, François; Chugai, Nikolai; Grebenev, Sergei; Bravo Guil, Eduardo; Sazonov, Sergei; Renaud, Matthieu
A type Ia supernova is thought to be a thermonuclear explosion of either a single carbon–oxygen white dwarf or a pair of merging white dwarfs. The explosion fuses a large amount of radioactive 56Ni. After the explosion, the decay chain from 56Ni to 56Co to 56Fe generates ¿-ray photons, which are reprocessed in the expanding ejecta and give rise to powerful optical emission. Here we report the detection of 56Co lines at energies of 847 and 1,238 kiloelectronvolts and a ¿-ray continuum in the 200–400 kiloelectronvolt band from the type Ia supernova 2014J in the nearby galaxy M82. The line...

10. Comparison of theoretical white dwarf cooling timescales (Research Note) - Salaris, Maurizio; Althaus, Leandro Gabriel; García-Berro Montilla, Enrique
Context. An accurate assessment of white dwarf cooling times is paramount so that white dwarf cosmochronology of Galactic populations can be put on more solid grounds. This issue is particularly relevant in view of the enhanced observational capabilities provided by the next generation of extremely large telescopes, that will offer more avenues to use white dwarfs as probes of Galactic evolution and test-beds of fundamental physics. Aims. We estimate for the first time the consistency of results obtained from independent evolutionary codes for white dwarf models with fixed mass and chemical stratification, when the same input physics is employed in...

11. The post-merger magnetized evolution of white dwarf binaries: The double-degenerate channel of sub-Chandrasekhar type Ia supernovae and the formation of magnetized white dwarfs - Ji, Suoqing; Fisher, Robert T.; García-Berro Montilla, Enrique; Tzeferacos, Petros; Jordan, George C.; Lee, Dongwook; Loren Aguilar, Pablo; Cremer, Pascal; Behrends, Jan
Type Ia supernovae (SNe Ia) play a crucial role as standardizable cosmological candles, though the nature of their progenitors is a subject of active investigation. Recent observational and theoretical work has pointed to merging white dwarf binaries, referred to as the double-degenerate channel, as the possible progenitor systems for some SNe Ia. Additionally, recent theoretical work suggests that mergers which fail to detonate may produce magnetized, rapidly rotating white dwarfs. In this paper, we present the first multidimensional simulations of the post-merger evolution of white dwarf binaries to include the effect of the magnetic field. In these systems, the two...

12. Measurement of the 58Ni(a, g) 62Zn reaction and its astrophysical impact - Quinn, Samantha J.; Spyrou, Artemis; Bravo Guil, Eduardo
Cross section measurements of the 58Ni(a,¿)62Zn reaction were performed in the energy range Ea=5.5to9.5 MeV at the Nuclear Science Laboratory of the University of Notre Dame, using the NSCL Summing NaI(Tl) detector and the ¿-summing technique. The measurements are compared to predictions in the statistical Hauser-Feshbach model of nuclear reactions using the SMARAGD code. It is found that the energy dependence of the cross section is reproduced well but the absolute value is overestimated by the prediction. This can be remedied by rescaling the a width by a factor of 0.45. Stellar reactivities were calculated with the rescaled a width...

13. Measurement of the 58Ni(a, g) 62Zn reaction and its astrophysical impact - Quinn, Samantha J.; Spyrou, Artemis; Bravo Guil, Eduardo
Cross section measurements of the 58Ni(a,¿)62Zn reaction were performed in the energy range Ea=5.5to9.5 MeV at the Nuclear Science Laboratory of the University of Notre Dame, using the NSCL Summing NaI(Tl) detector and the ¿-summing technique. The measurements are compared to predictions in the statistical Hauser-Feshbach model of nuclear reactions using the SMARAGD code. It is found that the energy dependence of the cross section is reproduced well but the absolute value is overestimated by the prediction. This can be remedied by rescaling the a width by a factor of 0.45. Stellar reactivities were calculated with the rescaled a width...

14. Modulación de fase para interferometría láser homodina - Terán Miranda, Marcelo
[ANGLÈS] Gravitational waves were predicted by Albert Einstein as a direct implication of the theory of General Relativity (1915). Although there are compelling experimental evidences of its existence, its detection has not been possible to the date. LISA (Laser interferometer Space Antenna) mission and its precursor mission LISA Pathfinder were designed as a complementary to terrestrial detectors, like LIGO and VIRGO, in order to obtain direct detection of gravitational waves at the frequency range of 100 μHz < f < 0.1 Hz. In this spectral range, the Universe is rich in gravitational waves sources and the sensitivity of terrestrial detectors...

15. The effects of metallicity on the Galactic disk population of white dwarfs - Cojocaru, Elena Ruxandra; Torres Gil, Santiago; Isern Vilaboy, Jordi; García-Berro Montilla, Enrique
Context. It has been known for a long time that stellar metallicity plays a significant role in the determination of the ages of the different Galactic stellar populations, when main sequence evolutionary tracks are employed. Aims. Here, we analyze the role that metallicity plays on the white dwarf luminosity function of the Galactic disk, which is often used to determine its age. Methods. We employ a Monte Carlo population synthesis code that accounts for the properties of the population of Galactic disk white dwarfs. Our code incorporates the most up-to-date evolutionary cooling sequences for white dwarfs with hydrogen-rich and hydrogen-deficient...

16. A search for neutrino emission from the Fermi bubbles with the ANTARES telescope - Adrian Martinez, Silvia; Albert, A.; Al Samarai, Imen; André, Michel; Anton, G.; Anvar, S.; Ardid, M.; Astraatmadja, T.; Baret, B.; Basa, S.; Bertin, V.; Biagi, S.; Bogazzi, C.; Bouhou, B.; Brunner, J.; Morganti, M.; Schmidt, J.; Stolarczyk, Th.
Analysis of the Fermi-LAT data has revealed two extended structures above and below the Galactic Centre emitting gamma rays with a hard spectrum, the so-called Fermi bubbles. Hadronic models attempting to explain the origin of the Fermi bubbles predict the emission of high-energy neutrinos and gamma rays with similar fluxes. The ANTARES detector, a neutrino telescope located in the Mediterranean Sea, has a good visibility to the Fermi bubble regions. Using data collected from 2008 to 2011 no statistically significant excess of events is observed and therefore upper limits on the neutrino flux in TeV range from the Fermi bubbles...

17. Automatic source detection in astronomical images - Masias Moyset, Marc
The use of automatic algorithms to detect astronomical sources (stars, galaxies, gas, dust or cosmic rays) becomes of great importance because of the increasing amount of astronomical images and the inefficiency and inaccuracy of manual inspection. We exhaustively analyze the state of the art on this topic, presenting a new classification of techniques and pointing out their main strengths and weaknesses. A complementary quantitative evaluation of some of the most remarkable methods found in the literature is also provided. Moreover, we present three different proposals based on different strategies to detect faint sources in radio images, and another proposal to...

18. Astronomia e Astrofísica em figuras - Petry, Mauricio Gasparin

19. The effects of metallicity on the Galactic disk population of white dwarfs - Cojocaru, Elena Ruxandra; Torres Gil, Santiago; Isern Vilaboy, Jordi; García-Berro Montilla, Enrique
Context. It has been known for a long time that stellar metallicity plays a significant role in the determination of the ages of the different Galactic stellar populations, when main sequence evolutionary tracks are employed. Aims. Here, we analyze the role that metallicity plays on the white dwarf luminosity function of the Galactic disk, which is often used to determine its age. Methods. We employ a Monte Carlo population synthesis code that accounts for the properties of the population of Galactic disk white dwarfs. Our code incorporates the most up-to-date evolutionary cooling sequences for white dwarfs with hydrogen-rich and hydrogen-deficient...

20. O ensino de fundamentos de astronomia e astrofísica na modalidade a distância para alunos de graduação - Müller, Alexei Machado
O número de cursos na modalidade a distância tem aumentado consideravelmente no mundo, porém existe um grande receio por parte de muitos que o ensino nessa modalidade tenha qualidade inferior ao apresentado na modalidade presencial. Contudo a qualidade do ensino não decorre da presença de todos os envolvidos num mesmo local, e sim da implementação de ações que facilitem o processo de aprendizagem. Esse trabalho teve como objetivo produzir um módulo didático, em hipermídia, para a disciplina de Fundamentos de Astronomia e Astrofísica, a ser ministrada na modalidade a distância aos alunos do curso de licenciatura em Física e a...

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