Mostrando recursos 141 - 160 de 194

  1. The upper mass limit for the formation of TP-SAGB stars and the dredge-out phenomenon

    Gil Pons, Pilar; Doherty, Carolyn L.
    We have computed the evolution of Super-AGB stars from the main sequence and up to a few hundred thermal pulses, with special attention to the low metallicity cases (Z = 10 10; 10 5; 10 4 and 10 3). Our computations have been performed using time– dependent mixing and new opacity tables that admit variations in the abundances of carbon and oxygen. By following the evolution along the main central burning stages and the early TP-SAGB, we resolve the upper mass limits for the formation of TP-SAGB stars and determine the mass range at which the dredge-out phenomenon occurs. This phenomenon involves the merger of a convective...

  2. The white dwarf cooling sequence of NGC 6791: an unique tool for stellar astrophysics

    García-Berro Montilla, Enrique; Torres Gil, Santiago; Renedo Rouco, Isabel; Camacho Díaz, Judit; Althaus, Leandro Gabriel; Córsico, Alejandro Hugo; Salaris, Maurizio; Isern Vilaboy, Jordi
    Context. NGC 6791 is a well-studied, metal-rich open cluster that is so close to us that it can be imaged down to luminosities fainter than that of the termination of its white-dwarf cooling sequence, thus allowing for an in-depth study of its white dwarf population. Aims. White dwarfs carry important information about the history of the cluster. We use observations of the white-dwarf cooling sequence to constrain important properties of the cluster stellar population, such as the existence of a putative population of massive helium-core white dwarfs, and the properties of a large population of unresolved binary white dwarfs. We also investigate the use...

  3. Un planeta con dos soles. ¿Tatooine o Kepler-16b?

    Moreno Lupiáñez, Manuel
    La existencia de un mundo con atardeceres dobles, similar al que se mostró en la película "Star Wars" hace más de 30 años, ya es un hecho científico. La misión Kepler, de la Nasa, ha logrado la primera detección directa de un planeta circumbinario (que orbita alrededor de dos estrellas a la vez) a 200 años luz de distancia de la Tierra.

  4. Absolute determination of the Na-22(rho, gamma)Mg-23 reaction rate in novae

    José Pont, Jordi; Caggiano, J. A.; Hutcheon, D. A.; Vockenhuber, C.; Buchmann, L.; Sallaska, A.L.; Wrede, C.; Garcia, A.; Storm,, D. W.; Brown, T. A. D.; Ruiz, C.; Snover, K.A.; Ottewell, D.
    Gamma-ray telescopes in orbit around the earth are searching for evidence of the elusive radionuclide 22Na produced in novae. Previously published uncertainties in the dominant destructive reaction, 22Na(p,γ)23Mg, indicated new measurements in the proton energy range of 150 to 300 keV were needed to constrain predictions. We have measured the resonance strengths, energies, and branches directly and absolutely by using protons from the University of Washington accelerator with a specially designed beam line, which included beam rastering and cold vacuum protection of the 22Na implanted targets. The targets, fabricated at TRIUMF-ISAC, displayed minimal degradation over a ∼20 C bombardment as...

  5. The LISA pathfinder DMU and radiation monitor

    Wass, P.; Araujo, H.; Fernandez Sopuerta, Carlos; Sanjuan, J.; Ramos Castro, Juan José; Nofrarias, M.; Mateos, I.; Lloro, I.; Canizares, P.; Chmeissani, M.; Conchillo, A.; Díaz Aguiló, Marc; García-Berro Montilla, Enrique; Gesa, L.; Gibert, Fabien; Grimani, C.
    The LISA PathfinderDMU(Data Management Unit) flight model was formally accepted by ESA andASDon 11 February 2010, after all hardware and software tests had been successfully completed. The diagnostics items are scheduled to be delivered by the end of 2010. In this paper, we review the requirements and performance of this instrumentation, specially focusing on the Radiation Monitor and the DMU, as well as the status of their programmed use during mission operations, on which work is ongoing at the time of writing.

  6. Is the metallicity of their host galaxies a good measure of the metallicity of Type Ia supernovae?

    Bravo Guil, Eduardo; Badenes Montoliu, Carles
    The efficient use of Type Ia supernovae (SNIa) for cosmological studies requires knowledge of any parameter that can affect their luminosity in either systematic or statistical ways. Observational samples of SNIa commonly use the metallicity of the host galaxy, Zhost, as an estimator of the supernova progenitor metallicity, ZIa, that is one of the primary factors affecting SNIa magnitude. Here, we present a theoretical study of the relationship between ZIa and Zhost. We follow the chemical evolution of homogeneous galaxy models together with the evolution of the supernova rates in order to evaluate the metallicity distribution function, MDF( Z), i.e. the probability that the logarithm of the...

  7. Funció de distribució de les velocitats de les estrelles a l'entorn del Sol

    Cubarsí Morera, Rafael

  8. Secondary fe-peak nuclei in the tycho supernova remnant

    Badenes Montoliu, Carles; Bravo Guil, Eduardo; Hughes, J.P.
    The Mn to Cr mass ratio in supernova ejecta has recently been proposed as a tracer of Type Ia SN progenitor metallicity. We review the advantages and problems of this observable quantity, and discuss them in the framework of two Galactic supernova remnants: the well known Tycho SNR and W49B, an older object that has been tentatively classified as Type Ia. The fluxes of the Mn and Cr Ka lines in the X-ray spectra of these SNRs observed by the Suzaku and ASCA satellites suggest progenitors of supersolar metallicity for both objects.

  9. Monte Carlo simulations of the formation channels of SNeIb. PoS(SUPERNOVA)008

    Camacho Díaz, Judit; Torres Gil, Santiago; García-Berro Montilla, Enrique
    We present a Monte Carlo simulator of the population of binary stars within the solar neighborhood. We have used the most updated models for stellar evolution, a complete treatment of the Roche lobe over ow episodes, as well as a full implementation of the orbital evolution. Special emphasis has been placed on processes leading to the formation of binary systems in which one of the members is a white dwarf. As a preliminary application of our Monte Carlo simulator we have performed a statistical study of the scenarios leading to type Ib supernovae events within our Galaxy

  10. The elusive nature of the r-stars

    Domínguez, Inmaculada; Piersanti, Luciano; Cabezón Gómez, Rubén Martín; Zamora, O.; García Senz, Domingo; Abia, C.; Straniero, Oscar
    R stars are carbon stars, less luminous and hotter than the carbon stars evolving along the AGB phase. Thus, their carbon enrichment cannot be a consequence of the third dredge-up, a fact also in agreement with the lack of s-element enhancements in their envelopes. Since their discovery the absence of binaries has lead to the conclusion that a previous merger might play a fundamental role in the observed chemical composition, likely through non-standard mixing at the time of the He-flash. On the other hand numerical simulations, in which the He-flash is artificially located close to the edge of a degenerate...

  11. Estudio del horizonte local

    Ros Ferré, Rosa Maria
    El estudio del horizonte es fundamental para poder facilitar las primeras observaciones de los alumnos en un centro educativo. Un simple modelo, que debe realizarse para cada centro, nos permite facilitar el estudio y la comprensión de los primeros rudimentos astronómicos. El modelo construido se presenta a su vez como un sencillo modelo de reloj ecuatorial y a partir de él se pueden construir otros modelos (horizontal y vertical).

  12. Monte Carlo simulations of the binary white dwarf population: a progress report

    Camacho Díaz, Judit; Torres Gil, Santiago; García-Berro Montilla, Enrique

  13. Monte Carlo simulations of the post-common envelope white dwarf-main sequence binary population

    Camacho Díaz, Judit; Torres Gil, Santiago; García-Berro Montilla, Enrique; Zorotovic, Monica; Schreiber, Mathias R.
    Postprint (published version)

  14. The contribution of red dwarfs and white dwarfs to the halo dark matter

    Torres Gil, Santiago; Camacho Díaz, Judit; Isern Vilaboy, Jordi; García-Berro Montilla, Enrique

  15. The effects of the Observational Selection Criteria on the post common envelope white dwarf-main sequence binary population

    Camacho Díaz, Judit; Torres Gil, Santiago; García-Berro Montilla, Enrique; Zorotovic, Mónica; Schreiber, Mathias R.; Rebassa-Mansergas, Alberto
    We present a detailed Monte Carlo simulator of the Galactic population of binary stars. Preliminary results are presented for the white dwarf-main sequence (WD+MS) binary population resulting from a common envelope (CE) episode. We also study the effects of the observational selection criteria on different color-color diagrams, for different binding energy parameters, l , and common envelope efficiencies, aCE. Finally, we also compare our results with the identified population of white dwarf-main sequence binaries in the SDSS

  16. Algorithm specification for the Magnetic Diagnostics onboard LPF

    Díaz Aguiló, Marc; García-Berro Montilla, Enrique; Lobo Gutiérrez, José Alberto
    Document tècnic per la missió espacial LISA Pathfinder. Missió espacial de l'Agència Espacial Europea (ESA).

  17. Monte Carlo simulations of the binary white dwarf population: a progress report

    Camacho Díaz, Judit; Torres Gil, Santiago; García-Berro Montilla, Enrique
    We present a detailed Monte Carlo simulator of the population of binary stars within the solar neighborhood. We have used the most updated models for stellar evolution, a complete treatment of the Roche lobe overflow episodes, as well as a full implementation of the orbital evolution. Special emphasis has been placed on processes leading to the formation of binary systems in which one of the members is a white dwarf.

  18. Measurement of the 197-Au(n,gamma) cross section at n TOF: towards a new standard

    Calviño Tavares, Francisco; Cortés Rossell, Guillem Pere; Poch Parés, Agustí; Pretel Sánchez, Carme
    Two different detectors and techniques are employed at n TOF facility, at CERN, to improve the accuracy of the neutron capture cross section of 197Au(n,γ): a total absorption calorimeter and a set of C6D6. The accurate knowledge of this cross section is of great importance for all the (n,γ) reactions study. The neutron capture cross section and nuclear resonce parameters of the 197Au have been measured in the energy range of 1 eV to 1 kev. The present work shows in average a good agreement with evaluated data libraries, although sizeable differences have been observed for some resonances. Two new resonances have also been discovered....

  19. Simultaneous measurement of the neutron capture and fission yields of 233-U

    Calviño Tavares, Francisco; Cortés Rossell, Guillem Pere; Poch Parés, Agustí; Pretel Sánchez, Carme
    We have measured the neutron capture and fission cross section of 233U at the neutron time-of-flight facility n TOF at CERN in the energy range from 1 eV to 1 MeV with high accuracy by using a high performance 4π BaF2 Total Absorption Calorimeter (TAC) as a detection device. The method, based on the TAC energy response study, allowing to disentangle between γ’s originating from fission and capture will be presented as well as the first very preliminary results.

  20. Neutron resonance spectroscopy at n TOF at CERN

    Calviño Tavares, Francisco; Cortés Rossell, Guillem Pere; Poch Parés, Agustí; Pretel Sánchez, Carme
    Neutron resonance spectroscopy plays an important role in the investigation of neutron induced reaction cross sections and nuclear structure in the MeV excitation range. Neutron time-of-flight facilities are the most used installations to explore neutron resonances. In this paper we describe the basic features of neutron resonance spectroscopy together with recent results from the time-of-flight facility n TOF at CERN.

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