Mostrando recursos 121 - 140 de 194

  1. Reaction rates for the s-process neutron source Ne-22+alpha

    Longland, Richard Leigh; Iliadis, Christian; Karakas, A.I.
    The 22Ne(α, n)25Mg reaction is an important source of neutrons for the s-process. In massive stars responsible for the weak component of the s-process, 22Ne(α, n)25Mg is the dominant source of neutrons, both during core helium burning and in carbon-shell burning. For the main s-process component produced in asymptotic giant branch (AGB) stars, the 13C(α, n)16O reaction is the dominant source of neutrons operating during the interpulse period, with the 22Ne + α source affecting mainly the s-process branchings during a thermal pulse. Rate uncertainties in the competing 22Ne(α, n)25Mg and 22Ne(α, γ)26Mg reactions result in large variations of s-process...

  2. Recent advances in the modelling of classical novae and type I X-ray bursts

    José Pont, Jordi; Casanova Bustamante, Jordi; Parikh, Anuj Ramesh; García-Berro Montilla, Enrique
    Classical nova outbursts and type I X-ray bursts are thermonuclear stellar explosions driven by charged-particle reactions. Extensive numerical simulations of nova explosions have shown that the accreted envelopes attain peak temperatures between 0.1 and 0.4 GK, for about several hundred seconds, and therefore, their ejecta is expected to show signatures of significant nuclear activity. Indeed, it has been claimed that novae play some role in the enrichment of the interstellar medium through a number of intermediate-mass elements. This includes 17O, 15N, and 13C, systematically overproduced in huge amounts with respect to solar abundances, with a lower contribution to a number...

  3. Optimal low-thrust transfers between libration point orbits

    Ren, Yuan; Pergola, Pierpaolo; Fantino, Elena; Thiere, B.
    Over the past three decades, ballistic and impulsive trajectories between libration point orbits (LPOs) in the Sun–Earth–Moon system have been investigated to a large extent. It is known that coupling invariant manifolds of LPOs of two different circular restricted three-body problems (i.e., the Sun–Earth and the Earth–Moon systems) can lead to significant mass savings in specific transfers, such as from a low Earth orbit to the Moon’s vicinity. Previous investigations on this issuemainly considered the use of impulsive maneuvers along the trajectory. Here we investigate the dynamical effects of replacing impulsive V’s with low-thrust trajectory arcs to connect LPOs using invariant manifold dynamics. Our investigation shows that the...

  4. Estimating the rate and luminosity function of all classes of GRBs

    Balastegui Manso, Andreu; Canal, Ramon; Ruiz-Lapuente, Pilar
    The aim of the present work is to estimate the rate and luminosity functions of short, intermediate and long gamma-ray bursts (GRBs) by fitting their intensity distributions wih parameterized explosion rates and luminosity functions. The results show that the parameters of the rate and luminosity function for long GRBs can be calculated with an accuracy of 10-30%. However, some parameters of intermediate and short GRBs have large uncertainties. An important conclusion is that there was initially a large outburst in the frequency of long GRBs, and consequently a large outburst in the star-formation rate, if they come from collapsars. Finally,...

  5. Dynamical behavior of asteroids near resonance: the 4:1 gap and the 7:2 group

    Grau Sánchez, Miguel; González Casado, Guillermo
    A comparative study of the evolution of the Sun–Jupiter–Asteroid system near the 4:1 and 7:2 resonances is performed by means of two techniques that proceed differently from the Hamiltonian corresponding to the planar restricted elliptic three-body problem. One technique is based on the classical Schubart averaging while the other is based on a mapping method in which the perturbing part of the Hamiltonian is expanded and the resulting terms are ordered according to a weight function that depends on the powers of eccentricities and the coefficients of the terms. For the mapping method the effect of Saturn on the asteroidal evolution is introduced and the degree...

  6. Comparative testing of four ionospheric models driven with GPS measurements

    Zandbergen, R.; Feltens, Joachim; Angling, M; Jackson Booth, N; Jakowski, Norbert; Hoque, Mainul; Hernández Pajares, Manuel; Aragón Ángel, María Ángeles; Orús Pérez, Raül
    In the context of the European Space Agency/European Space Operations Centre funded Study “GNSS Contribution to Next Generation Global Ionospheric Monitoring,” four ionospheric models based on GNSS data (the Electron Density Assimilative Model, EDAM; the Ionosphere Monitoring Facility, IONMON v2; the Tomographic Ionosphere model, TOMION; and the Neustrelitz TEC Models, NTCM) have been run using a controlled set of input data. Each model output has been tested against differential slant TEC (dSTEC) truth data for high (May 2002) and low (December 2006) sunspot periods. Three of the models (EDAM, TOMION, and NTCM) produce dSTEC standard deviation results that are broadly consistent with each other and with standard deviation spreads...

  7. Star visibility and tracking from the Space Station

    Bernacca, Pier Luigi; Facchinetti, Claudia; Fantino, Elena
    Purpose of the present study is to provide algorithms for and examples of how to simulate star visibility and tracking by a Telescope attached to the main truss of the International Space Station (ISS). The sky visibility of a Telescope is limited by accommodation constraints on the truss, by obstructions caused by Station’s structural elements along with other payloads, by Sun and Moon’s light and by ram atomic Oxygen. It is also limited by Station’s orbit and attitude. The above limiting agents have been modeled vis-a-vis NASA nominal specifications and knowledge of the ambient environment. These models have been used to...

  8. Nucleosynthesis during the merger of white dwarfs and the origin of R Coronae Borealis stars

    Longland, Richard Leigh; Lorén Aguilar, Pablo; José Pont, Jordi; García-Berro Montilla, Enrique; Althaus, Leandro Gabriel; Isern Vilaboy, Jordi
    Many hydrogen-deficient stars are characterized by surface abundance patterns that are hard to reconcile with conventional stellar evolution. Instead, it has been suggested that they may represent the result of a merger episode between a helium and a carbon–oxygen white dwarf. In this Letter, we present a nucleosynthesis study of the merger of a 0.4M helium white dwarf with a 0.8M carbon–oxygen white dwarf, by coupling the thermodynamic history of Smoothed Particle Hydrodynamics particles with a post-processing code. The resulting chemical abundance pattern, particularly for oxygen and fluorine, is in qualitative agreement with the observed abundances in R Coronae Borealis...

  9. Improvement of retrieved FORMOSAT-3/COSMIC electron densities validated by ionospheric sounder measurements at Jicamarca

    Aragón Ángel, María Ángeles; Liou, Y.-A.; Lee, C.-C.; Reinisch, B.W.; Hernández Pajares, Manuel; Juan Zornoza, José Miguel; Sanz Subirana, Jaume
    Inversion techniques applied to GPS‐LEO radio occultation data allow the retrieval of accurate and worldwide‐distributed refractivity profiles, which, in the case of the ionosphere, can be converted into electron densities providing information regarding the electron content distribution in this atmospheric region. In order to guarantee the accuracy of the electron density retrievals, two key points should be taken into account: the horizontal gradients of the electronic distribution and the topside electron content above the LEO orbit. The deployment in April 2006 of the satellite Constellation Observing System for Meteorology Ionosphere and Climate (FORMOSAT‐3/COSMIC), carrying GPS receivers on board, provides valuable radio occultation data with global and almost uniform coverage...

  10. The influence of uncertainties in the O-15(alpha, gamma) Ne-19 reaction rate on models of type I X-Ray bursts

    Davids, B.; Cyburt, Richard H.; José Pont, Jordi; Mythili, Subramanian
    We present aMonte Carlo calculation of the astrophysical rate of the 15O(α,γ)19Ne reaction based on an evaluation of published experimental data. By considering the likelihood distributions of individual resonance parameters derived from measurements, estimates of upper and lower limits on the reaction rate at the 99.73% confidence level are derived in addition to the recommended, median value. These three reaction rates are used as input for three separate calculations of Type I X-ray bursts (XRBs) using spherically symmetric, hydrodynamic simulations of an accreting neutron star. In this way the influence of the 15O(α,γ)19Ne reaction rate on the peak luminosity, recurrence...

  11. Search for a diffuse flux of high-energy ¿µ with the ANTARES neutrino telescope

    Petrovic, J.; Piattelli, P.; Guillard, G.; Picot-Clemente, N.; Picq, C.; Neff, M.; Hallewell, G.; Palioselitis, D.; Halladjian, G.; Pavalas, G.E.; Heijboer, A.J.; Spurio, M.; Taiuti, M.; Lamare, P.; Stolarczyk, Th.; Larosa, G.; Kopper, C.; Kooijman, P.; Kulikowskiy, V.; Sapienza, P.; Kouchner, A.; Van Haren, H.; Schöck, F.; Bogazzi, C.; Bigongiari, C.; Biagi, S.; Vecchi, M.; Kappes, A.; Bertin, V.; Vannoni, G.; Katz, U.; Bazzotti, M.; Payre, P.; Van Elewyck, V.; Kalantar-Nayestanaki, N.; Basa, S.; Vallage, B.; Kalekin, O.; Baret, B.; De Jong, M.; Auer, R.; Kadler, M.; De Wolf, E.; Popa, V.; Aubert, J.J.; Wijnker, G.; Astraatmadja, T.; Vernin, P.; Bou-Cabo, M.; Hsu, C.C.; Tasca, L.; Höbl, J.; Toscano, S.; Herold, B.; Pradier, T.; Hernández Rey, J.J.; Tamburini, C.; Hello, Y.; Assis Jesus, A.C.; Aguilar, J.A.; Fuda, J.L.; Al Samarai, Imen; Galata, S.; Albert, A.; Gay, P.; André, Michel; Giacomelli, G.; Anghinolfi, M.; Gómez González, J.P.; Anton, G.; Graf, K.; Anvar, S.; Ardid, M.; Rujoiu, M.; Russo, G.V.; Roensch, K.; Rostovtsev, A.; Fritsch, U.; Riccobene, Giorgio; Folger, F.; Richardt, C.; Flaminio, V.; Racca, C.; Fehr, F.; Reed, C.; Salesa, F.; Drouhin, D.; Presani, E.; Eberl, T.; Dornic, D.; Dorosti, Q.; Escoffier, S.; Emanuele, U.; Ernenwein, J.P.; Dekeyser, I.; Donzaud, C.; Deschamps, A.; Cottini, N.; Coyle, Pascal; Curtil, C.; Decowski, M.P.; Chiarusi, T.; Circella, M.; Coniglione, R.; Costantini, H.; Charvis, Ph.; Cecchini, S.; Carr, J.; Cârloganu, C.; Carminati, G.; Camarena, F.; Capone, A.; Brunner, J.; Busto, J.; Bouwhuis, M.C.; Brown, A.M.; Naumann, C.; Yepes, H.; Motz, H.; Zaborov, D.; Zornoza, J.D.; Zúñiga, J.; Martinez Mora, J.A.; Mazure, A.; Marcelin, M.; Margiotta, A.; Morganti, M.; Moscoso, L.; Meli, A.; Montarulli, T.; Mangano, S.; Lucarelli, F.; Loucatos, S.; Lefèvre, D.; Shanidze, R.; Lim, G.; Schuller, J.P.; Lo Presti, D.; Spies, A.; Loehner, H.; Simeone, F.; Steijger, J.J.M.; Lahmann, R.
    A search for a diffuse flux of astrophysical muon neutrinos, using data collected by the ANTARES neutrino telescope is presented. A (0.83 × 2π) sr sky was monitored for a total of 334 days of equivalent live time. The searched signal corresponds to an excess of events, produced by astrophysical sources, over the expected atmospheric neutrino background. The observed number of events is found compatible with the background expectation. Assuming an E−2 flux spectrum, a 90% c.l. upper limit on the diffuse νμ flux of E2Φ90% = 5.3 × 10−8 GeVcm−2 s−1 sr−1 in the energy range 20 TeV–2.5 PeV is obtained. Other signal models with...

  12. The Berduc L6 chondrite fall: meteorite characterization, trajectory, and orbital elements

    Trigo Rodríguez, Josep Maria; Llorca Piqué, Jordi; Madiedo, J. M.; Tancredi, Gonzalo; Edwards, Wayne; Rubin, Alan E.; Weber, Patrick
    Abstract–The fall of the Berduc meteorite took place on April 7, 2008, at 01 h 02 min 28 s ± 1 s UTC. A daylight fireball was witnessed by hundreds of people from Argentina and Uruguay, and also recorded by an infrasound array in Paraguay. From the available data, the fireball trajectory and radiant have been reconstructed with moderate accuracy. The modeled trajectory was tested to fit the infrasound and strewn field data. From the computed apparent radiant a = 87 ± 2 and d = )11 ± 2 and taking into account a range of plausible initial velocities, we obtained a range of orbital solutions....

  13. The complex structure of HH 110 as revealed from Integral Field Spectroscopy

    López, R.; García-Lorenzo, B.; Sánchez, S.F.; Gomez, G.; Estalella Boadella, Robert; Riera Mora, M. Ángeles

  14. New cooling sequences for old white dwarfs

    Renedo Rouco, Isabel; Althaus, Leandro Gabriel; Miller Bertolami, Marcelo M; Romero, A.D.; Córsico, Alejandro Hugo; Rohrmann, Rene Daniel; García-Berro Montilla, Enrique
    We present full evolutionary calculations appropriate for the study of hydrogen-rich DA white dwarfs. This is done by evolving white dwarf progenitors from the zero-age main sequence, through the core hydrogen-burning phase, the helium-burning phase, and the thermally pulsing asymptotic giant branch phase to the white dwarf stage. Complete evolutionary sequences are computed for a wide range of stellarmasses and for two different metallicities, Z = 0.01, which is representative of the solar neighborhood, and Z = 0.001, which is appropriate for the study of old stellar systems, like globular clusters. During the white dwarf cooling stage, we self-consistently compute the phase in which nuclear reactions...

  15. Revisiting the theoretical DBV (V777 Her) instability strip: The MLT theory of convection

    Córsico, Alejandro Hugo; Althaus, Leandro Gabriel; Miller Bertolami, Marcelo M; García-Berro Montilla, Enrique
    We reexamine the theoretical instability domain of pulsating DB white dwarfs (DBV or V777 Her variables). We performed an extensive g-mode nonadiabatic pulsation analysis of DB evolutionary models considering a wide range of stellar masses, for which the complete evolutionary stages of their progenitors from the ZAMS, through the thermally pulsing AGB and born-again phases, the domain of the PG1159 stars, the hot phase of DO white dwarfs, and then the DB white dwarf stage have been considered. We explicitly account for the evolution of the chemical abundance distribution due to time-dependent chemical diffusion processes. We examine the impact of...

  16. Seismological constraints on the high-gravity DOV stars PG 2131+066 and PG 1707+427

    Córsico, Alejandro Hugo; Althaus, Leandro Gabriel; Miller Bertolami, Marcelo M; García-Berro Montilla, Enrique
    A seismological study of the pulsating PG1159 stars PG2131+066 and PG 1707+427 is presented. We perform extensive adiabatic computations of g-mode pulsation periods of PG1159 evolutionary models with stellar masses ranging from 0.530 to 0.741M⊙. We constrain the stellar mass of PG2131+066 and PG 1707+427 by comparing the observed period spacing of each star with the theoretical asymptotic period spacings and with the average of the computed period spacings. We also employ the individual observed periods to find representative seismological models for both stars.

  17. Testing the initial-final mass relationship of white dwarfs

    Catalán Ruiz, Silvia; Isern Vilaboy, Jordi; García-Berro Montilla, Enrique; Ribas Canudas, Ignasi
    In this contribution we revisit the initial-final mass relationship of white dwarfs, which links the mass of a white dwarf with that of its progenitor in the main-sequence. Although this function is of paramount importance to several fields in modern astrophysics, it is still not well constrained either from the theoretical or the observational points of view. We present here a revision of the present semi-empirical initial-final mass relationship using all the available data and including our recent results obtained from studying white dwarfs in common proper motion pairs. We have also analyzed the results obtained so far to provide some clues on the dependence of this...

  18. The gravitational wave emission from white dwarf interactions in globular clusters

    Lorén Aguilar, Pablo; Lobo Gutiérrez, José Alberto; Isern Vilaboy, Jordi; García-Berro Montilla, Enrique
    In the dense central regions of globular clusters close encounters of two white dwarfs are relatively frequent. The estimated frequency is one or more strong encounters per star in the lifetime of the cluster. Such encounters should be then potential sources of gravitational wave radiation. Thus, it is foreseeable that these collisions could be either individually detected by LISA or they could contribute significantly to the background noise of the detector. We compute the pattern of gravitational wave emission from these encounters for a sufficiently broad range of system parameters, namely the masses, the relative velocities and the distances of the two white dwarfs involved in the...

  19. Optimal Interferometric Maneuvers for Distributed Telescopes

    Díaz Aguiló, Marc; Mandy, C; Sáenz Otero, Alvar; Miller, D
    The scientfic community has proposed several missions to expand our knowledge about the universe, its formation and search for distant Earth-like planets. Most of the present space-based observation missions have reached angular resolution limits, therefore the potential benefits concerning angular resolution and intensity that can be reaped from the realization of interferometry within a distributed satellite telescope have led to the proposal of several multi-spacecraft systems. Among these missions synthetic imaging space based interferometers, consisting of multiple telescope apertures flying in controlled formation in order to combine received information from each of the flotilla members are nowadays the subject of interesting research. The objective of synthesizing...

  20. Population Synthesis of Post-Common Envelope White-Dwarf-Main-Sequence Binaries in the Sloan Digital Sky Survey

    Torres Gil, Santiago; Camacho Díaz, Judit; Rebassa-Mansergas, Alberto; Zorotovic, Monica; Schreiber, Mathias R.; García-Berro Montilla, Enrique

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