Transitions between symmetric and nonsymmetric regimes in binary-mixture convection
- Meca Alvarez, Esteban; Mercader Calvo, María Isabel; Ramírez de la Piscina Millán, Laureano
We present here a comprehensive picture of the different bifurcations found for small to moderate Rayleigh number in binary-mixture convection with lateral heating and negative separation ratio (S). The present work connects the symmetric regime found for pure fluid (S=0)[Mercader et al 2005] with the fundamentally nonsymmetric regime found for S=-1 [Meca et al 2004a-2004b]. We give a global context as well as an interpretation for the different associations of bifurcations found, and in particular we interpret an association of codimension-two bifurcations in terms of a higher codimension
bifurcation never found, to our knowledge, in the study of an extended system.
Novel ionospheric activity indicator specifically tailored for GNSS users
- Sanz Subirana, Jaume; Juan Zornoza, José Miguel; González Casado, Guillermo; Prieto Cerdeira, Roberto; Schlüter, S.; Orús Pérez, Raul
This work introduces a novel ionospheric activity indicator useful for identifying disturbed periods affecting performance for GNSS users, at regional level. This indicator is based in the “Along Arc TEC Rate (AATR) and can be easily computed from GNSS data. The AATR indicator has been assessed over more than one Solar Cycle (2002-2013) involving 140 receivers distributed world-wide. Results show that it is well correlated with the ionospheric activity and, unlike other global indicators linked to the geomagnetic activity (i.e. DST, Ap), it is sensitive to regional behaviour the ionosphere and identifies specific effects on GNSS users. Moreover from a...
Super- and massive AGB stars - IV. Final fates initial-to-final mass relation
- Doherty, Carolyn L.; Gil Pons, Pilar; Siess, Lionel; Lattanzio, John C.; Lau, Herbert B.
We explore the final fates of massive intermediate-mass stars by computing detailed stellar models from the zero-age main sequence until near the end of the thermally pulsing phase. These super-asymptotic giant branch (super-AGB) and massive AGB star models are in the mass range between 5.0 and 10.0 M circle dot for metallicities spanning the range Z = 0.02-0.0001. We probe the mass limits M-up, M-n and M-mass, the minimum masses for the onset of carbon burning, the formation of a neutron star and the iron core-collapse supernovae, respectively, to constrain the white dwarf/electron-capture supernova (EC-SN) boundary. We provide a theoretical...
White dwarf evolutionary sequences for low-metallicity progenitors: The impact of third dredge-up
- Althaus, Leandro G.; Camisassa, Maria E; Miller Bertolami, Marcelo M; Corsico, Alejandro H.; García-Berro Montilla, Enrique
Context. White dwarfs are nowadays routinely used as reliable cosmochronometers, allowing several stellar populations to be dated.; Aims. We present new white dwarf evolutionary sequences for low-metallicity progenitors. This is motivated by the recent finding that residual H burning in low-mass white dwarfs resulting from Z = 0.0001 progenitors is the main energy source over a significant part of their evolution.; Methods. White dwarf sequences have been derived from full evolutionary calculations that take the entire history of progenitor stars into account, including the thermally pulsing and the post-asymptotic giant branch (AGB) phases.; Results. We show that for progenitor metallicities...
Constraining the double-degenerate scenario for Type Ia supernovae from merger ejected matter
- Levanon, Naveh; Soker, Noam; García-Berro Montilla, Enrique
We follow the mass expelled during the WD-WD merger process in a particular case of the double-degenerate (DD) scenario for Type Ia supernovae (SNe Ia), and find that the interaction of the SN ejecta with the resulting wind affects the early (first day) light-curve in a way that may be in conflict with some SN Ia observations, if the detonation occurs shortly after the merger, i.e. (10(3) s less than or similar to t(exp) less than or similar to 1 d). The main source of the expelled mass is a disc-wind, or jets that are launched by the accretion disc...
White dwarf dynamical interactions
- Aznar Siguan, Gabriela
Merging white dwarfs is a promising channel to trigger Type Ia supernovae, known as the double degenerate scenario. Supernovae are stellar explosions that radiate as much energy as any ordinary star is expected to emit over its entire life span, outshining briefly the whole hosting galaxy. They enrich the interstellar medium with higher mass elements and trigger the formation of new stars by the produced expanding shock. Additionally, Type Ia supernovae have been used as standard candles and have allowed the discovery that the universe was expanding at an accelerating rate. Despite the important role that Type Ia supernovae play...
Super and massive AGB stars - III. nucleosynthesis in metal-poor and very metal-poor stars - Z = 0.001 and 0.0001
- Doherty, Carolyn L.; Gil Pons, Pilar; Lau, Herbert B.; Lattanzio, John C.; Siess, Lionel; Campbell, Simon W
We present a new grid of stellar models and nucleosynthetic yields for super-AGB stars with metallicities Z = 0.001 and 0.0001, applicable for use within galactic chemical evolution models. Contrary to more metal-rich stars where hot bottom burning is the main driver of the surface composition, in these lower metallicity models the effect of third dredge-up and corrosive second dredge-up also have a strong impact on the yields. These metal-poor and very metal-poor super-AGB stars create large amounts of 4He, 13C, 14N and 27Al as well as the heavy magnesium isotopes 25Mg and 26Mg. There is a transition in yield...
Determinación y parametrización de propiedades radiativas de plasmas para la simulación y análisis de experimentos de Astrofísica de Laboratorio
- Espinosa Vivas, Guadalupe
Programa de doctorado: Sistemas inteligentes y aplicaciones numéricas en Ingeniería
Comunicaciones presentadas en la IV Asamblea Nacional de Astronomía y Astrofísica, Santiago de Compostela
- Sevilla, Miguel J.; Camacho, Antonio G.; Romero, P.
- Deformación de una tierra elástica por efecto de marea.
- Comparación de series de nutación.
- Programa "ARIES 2 ML" para reducción de posiciones de estrellas.
Homothetic motions and Newtonian cosmology
- Jaen Herbera, Javier; Molina Compte, Alfred
We construct a homothetic covariant Newtonian gravitation theory which unifies inertial homothetic forces and gravitational fields. This is achieved through an equivalence principle based on a local homothetic frame of motion. As a consequence, we can obtain a coherent Newtonian cosmology which admits a cosmological principle and leads to the Friedman equations for a dust universe. Finally we prove that this gravity theory can be obtained as the non-relativistic limit of a class of metrics in General Relativity. The Friedmann–Lemaître–Robertson–Walker metric and its limit are also studied.
The unreasonable effectiveness of experiments in constraining nova nucleosynthesis
- Parikh, Anuj Ramesh
Classical nova explosions arise from thermonuclear ignition in the envelopes of accreting white dwarfs in close binary star systems. Detailed observations of novae have stimulated numerous studies in theoretical astrophysics and experimental nuclear physics. These phenomena are unusual in nuclear astrophysics because most of the thermonuclear reaction rates thought to be involved are constrained by experimental measurements. This situation allows for rather precise statements to be made about which measurements are still necessary to improve the nuclear physics input to astrophysical models. We briefly discuss desired measurements in these environments with an emphasis on recent experimental progress made to better...
Latest generation white dwarf cooling models : theory and applications
- Renedo Rouco, Isabel
White dwarfs are the most common stellar evolutionary end-point. Moreover, they can be considered as reliable cosmic clocks to infer the age of a wide variety of stellar populations, including globular and open clusters. Consequently, there is a considerable interest in the study of white dwarf cooling models.
In this thesis we used two different approaches. From a theorical perspective, we computed a set of new cooling white dwarfs sequences which incorporates the most up-to-date physical inputs for precision white dwarf cosmochronology and for asteroseismological studies of ZZ Ceti stars. Moreover, we studied the role of 22Ne diffusion in the...
Recuperación de información astronómica : nuevas perspectivas de análisis de la cartografía celeste histórica
- Alonso Lifante, María Pilar
La mejora de la descripción de contenidos de recursos especializados en general, y de astronómicos en particular, es todavía una asignatura pendiente de las Ciencias de la Documentación. Actualmente existe gran cantidad de información astronómica histórica de interés recogida en diversos tipos de documentos que se conservan en archivos y bibliotecas astronómicas de todo el mundo. Entre estos documentos se encuentran los denominados catálogos y atlas de estrellas, así como imágenes astrofotográficas, todavía compilados en la actualidad aunque en formatos bien diferentes y con datos mucho más precisos. Sin embargo, las medidas procedentes de observaciones varios siglos atrás siguen atrayendo...
Underground study of the 17O(p,alpha)18F reaction relevant for explosive hydrogen burning
- Di Leva, A; Scott, D.A.; Caciolli, A.; Formicola, A.; Strieder, F.; Aliotta, M.; Anders, M.; Bemmerer, D.; Broggini, C.; Corvisiero, P.; Elekes, Z.; Fulop, Zs.; Gervino, G.; Guglielmetti, G.; Gustavino, C.; Gyurky, Gy.; Imbriani, G.; José Pont, Jordi; Junker, M.; et al., .
The 17O(p,γ )18F reaction affects the production of key isotopes (e.g., 18F and 18O) in the explosive hydrogen burning that powers classical novae. Under these explosive conditions, the reaction rate is dominated by contributions from a narrow resonance at Ec.m.= 183 keV and by the combined contributions of direct capture
and low-energy tails of broad resonances. At present, the astrophysical reaction rate is not well constrained because of the lack of data in the energy region appropriate to classical novae.
Procesos para una Astronomía que le aporte a Colombia
- Duque Escobar, Gonzalo
High-resolution smoothed particle hydrodynamics simulations of the merger of binary white dwarfs
- Lorén Aguilar, Pablo; Isern Vilaboy, Jordi; García-Berro Montilla, Enrique
Context. The coalescence of two white dwarfs is the final outcome of a sizeable fraction of binary stellar systems. Moreover, this
process has been proposed to explain several interesting astrophysical phenomena.
Aims. We present the results of a set of high-resolution simulations of the merging process of two white dwarfs.
Methods. We use an up-to-date Smoothed Particle Hydrodynamics code which incorporates very detailed input physics and an
improved treatment of the artificial viscosity. Our simulations have been done using a large number of particles (~ 4 × 105
cover the full range of masses and chemical compositions of the coalescing white dwarfs. We also...
Sinergia y pertinencia en las ciencias básicas
- Duque Escobar, Gonzalo
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
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...
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...