Publications (13)94.34 Total impact
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Article: Explaining the type Ia supernova PTF 11kx with a violent-prompt merger scenario
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ABSTRACT: We argue that the multiple shells of circumstellar material (CSM) and the supernovae (SN) ejecta interaction with the CSM starting 59 days after the explosion of the Type Ia SN (SN Ia) PTF 11kx, are best described by a violent prompt merger. In this prompt merger scenario the common envelope (CE) phase is terminated by a merger of a WD companion with the hot core of a massive asymptotic giant (AGB) star. In most cases the WD is disrupted and accreted onto the more massive core. However, in the rare cases where the merger takes place when the WD is denser than the core, the core will be disrupted and accreted onto the cooler WD. In such cases the explosion might occur with no appreciable delay, i.e., months to years after the termination of the CE phase. This, we propose, might be the evolutionary route that could lead to the explosion of PTF 11kx. This scenario can account for the very massive CSM within ~1000 AU of the exploding PTF 11kx star, for the presence of hydrogen, and for the presence of shells in the CSM.07/2012; -
Article: An upper limit to the secular variation of the gravitational constant from white dwarf stars
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ABSTRACT: A variation of the gravitational constant over cosmological ages modifies the main sequence lifetimes and white dwarf cooling ages. Using an state-of-the-art stellar evolutionary code we compute the effects of a secularly varying G on the main sequence ages and, employing white dwarf cooling ages computed taking into account the effects of a running G, we place constraints on the rate of variation of Newton's constant. This is done using the white dwarf luminosity function and the distance of the well studied open Galactic cluster NGC 6791. We derive an upper bound G'/G ~ -1.8 10^{-12} 1/yr. This upper limit for the secular variation of the gravitational constant compares favorably with those obtained using other stellar evolutionary properties, and can be easily improved if deep images of the cluster allow to obtain an improved white dwarf luminosity function.05/2011; -
Article: A white dwarf cooling age of 8 Gyr for NGC 6791 from physical separation processes.
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ABSTRACT: NGC 6791 is a well studied open cluster that it is so close to us that can be imaged down to very faint luminosities. The main-sequence turn-off age ( approximately 8 Gyr) and the age derived from the termination of the white dwarf cooling sequence ( approximately 6 Gyr) are very different. One possible explanation is that as white dwarfs cool, one of the ashes of helium burning, (22)Ne, sinks in the deep interior of these stars. At lower temperatures, white dwarfs are expected to crystallize and phase separation of the main constituents of the core of a typical white dwarf ((12)C and (16)O) is expected to occur. This sequence of events is expected to introduce long delays in the cooling times, but has not hitherto been proven. Here we report that, as theoretically anticipated, physical separation processes occur in the cores of white dwarfs, resolving the age discrepancy for NGC 6791.Nature 05/2010; 465(7295):194-6. · 36.28 Impact Factor -
Article: 16th European White Dwarfs Workshop
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ABSTRACT: The 16th European Workshop on White Dwarfs was held in Barcelona, Spain, from 30 June to 4 July 2008 at the premises of the UPC. Almost 120 participants from Europe (France, Germany, United Kingdom, Italy, and several others), America (USA, Canada, Argentina, Brazil, and Chile), and other continents (Australia, South Africa, . . . ) attended the workshop. Among these participants were the most relevant specialists in the field. The topics covered by the conference were: White dwarf structure and evolution Progenitors and Planetary Nebulae White dwarfs in binaries: cataclysmic variables, double degenerates and other binaries White dwarfs, dust disks and planetary systems Atmospheres, chemical composition, magnetic fields Variable white dwarfs White dwarfs in stellar clusters and the halo White Dwarfs as SNIa progenitors The programme included 54 talks, and 45 posters. The oral presentations were distributed into the following sessions: Luminosity function, mass function and populations White dwarf structure and evolution White dwarf ages White dwarf catalogs and surveys Central stars of planetary nebulae Supernovae progenitors White dwarfs in novae and CVs Physical processes in white dwarfs and magnetic white dwarfs Disks, dust and planets around white dwarfs Pulsating white dwarfs Additionally we had a special open session about Spitzer and white dwarfs. The Proceedings of the 16th European Workshop on White Dwarfs are representative of the current state-of-the-art of the research field and include new and exciting results. We acknowledge the very positive attitude of the attendants to the workshop, which stimulated very fruitful discussions that took place in all the sessions and after the official schedule. Also, the meeting allowed new collaborations tp start that will undoubtedly result in significant advances in the research field. We also acknowledge the willingness of the participants to deliver their contributions before the final deadline. We sincerely thank them. The white dwarf community has been steadily growing since the first white dwarf workshop, held in Kiel (Germany) in 1974. Some of the participants in the first colloquium have already effectively retired; others – although officially retired – continue to attend successive workshops, Professor Weidemann, one of the first organizers, being a leading example. We hope we will be able to continue counting on them for many years. A very graphical view of the evolution of the field can be found in the homepage of Professor Detlev Koester, who has collected pictures of almost all the previous workshops:. Additionally, several astronomers coming from related fields have joined our (not so) small community. Most importantly, several generations of young scientists gave their first talks in these workshops. In summary our community is an active one, and we have close, durable and solid ties of friendship. We are optimistic and we foresee that the spirit of the previous workshops will continue in future editions. We would like to express our deepest gratitude to our sponsors: The Universitat Politècnica de Catalunya (UPC), the Institut de Ciències de l'Espai (CSIC), the Institute for Space Studies of Catalonia (IEEC), the Spanish Ministry of Education and Science, the Generalitat de Catalunya, the Ajuntament de Barcelona, the School of Civil Engineering of Barcelona and UPCnet. Finally, the IEEC staff and our graduate students have enthusiastically supported the organization of the workshop in every single detail; without them we would have not succeeded. We thank them especially. Also, we acknowledge the task of the Scientific Organizing Committee, which gave their full support in all the scientific tasks. Enrique García-Berro, UPC Margarida Hernanz, ICE (CSIC) Jordi Isern, ICE (CSIC) Santiago Torres, UPC EditorsJournal of Physics Conference Series 07/2009; 172(1):011001. -
Article: The white dwarf luminosity function – II. The effect of the measurement errors and other biases
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ABSTRACT: The disc white dwarf luminosity function is an important tool for studying the solar neighbourhood, since it allows the determination of several Galactic parameters, the most important one being the age of the Galactic disc. However, only the method has been employed so far for observationally determining the white dwarf luminosity function, whereas for other kind of luminosity functions several other methods have been frequently used. Moreover, the procedures to determine the white dwarf luminosity function are not free of biases. These biases have two different origins: they can either be of statistical nature or a consequence of the measurement errors. In a previous paper we carried out an in-depth study of the first category of biases for several luminosity function estimators. In this paper we focus on the biases introduced by the measurement errors and on the effects of the degree of contamination of the input sample used to build the disc white dwarf luminosity function by different kinematical populations. To assess the extent of these biases we use a Monte Carlo simulator to generate a controlled synthetic population and analyse the behaviour of the disc white dwarf luminosity function for several assumptions about the magnitude of the measurement errors and for several degrees of contamination, comparing the performances of the most robust luminosity function estimators under such conditions.Monthly Notices of the Royal Astronomical Society 07/2007; 378(4):1461 - 1470. · 4.90 Impact Factor -
Chapter: Classification of the White Dwarf Populations Using Neural Networks
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ABSTRACT: The existence of an observational luminosity function for halo white dwarfs could provide valuable information about the age, the star formation rate and the initial mass function of the halo population. However, the main problem is the scarce number of white dwarfs already identified as halo stars. We use an artificial intelligence algorithm to classify the population of spectroscopically identified white dwarfs [1], thus allowing us to identify potential halo white dwarfs and to improve the significance of its luminosity function.02/2006: pages 391-393; -
Article: Simulating Gaia performances on white dwarfs
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ABSTRACT: One of the most promising space missions of the European Space Agency is the astrometric satellite Gaia, which will provide very precise astrometry and multicolour photometry, for all 1.3 billion objects to V∼ 20, and radial velocities with accuracies of a few km s−1 for most stars brighter than V∼ 17. Consequently, full homogeneous six-dimensional phase-space information for a huge number of stars will become available. Our Monte Carlo simulator has been used to estimate the number of white dwarfs potentially observable by Gaia. From this we assess the white dwarf luminosity functions that Gaia will obtain and discuss in depth the scientific returns of Gaia in the specific field of white dwarf populations. Scientifically attainable goals include, among others, a reliable determination of the age of the Galactic disc, a better knowledge of the halo of the Milky Way and the reconstruction of the star formation history of the Galactic disc. Our results also demonstrate the potential impact of a mission such as Gaia within the context of current understanding of white dwarf cooling theory.Monthly Notices of the Royal Astronomical Society 06/2005; 360(4):1381 - 1392. · 4.90 Impact Factor -
Chapter: Number Counts of White Dwarfs: The Impact of GAIA
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ABSTRACT: In the next years, several space missions will be devoted to measure with very high accuracy the motions of a sizeable fraction of the stars of our Galaxy. The most promising one is the ESA astrometric satellite GAIA, which will provide very precise astrometry (< 10 μas in parallax and < 10 μas yr−1 in proper motion at V ∼ 15, increasing to 0.2 mas yr−1 at V ∼ 20) and multicolor photometry, for all 1.3 billion objects to V ∼ 20, and radial velocities with accuracies of a few km s−1 for most stars brighter than V ∼ 17. Consequently, full homogeneous six-dimensional phase-space information for a huge number of white dwarfs will become available. Our Monte Carlo simulator has been used to estimate the number of white dwarfs potentially observable by GAIA. Our results show which could be the impact of a mission like GAIA in the current understanding of our Galaxy. Scientific attainable goals include, among others, a reliable determination of the age of our galactic disk, a better knowledge of the structure of the halo of the Milky Way or the reconstruction of the past history of the Star Formation Rate of the galactic disk.12/2004: pages 15-24; -
Article: High‐proper‐motion white dwarfs and halo dark matter
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ABSTRACT: The interpretation of the old, cool white dwarfs recently found by Oppenheimer et al. is still controversial. Whereas these authors claim that they have finally found the elusive ancient-halo white dwarf population that contributes significantly to the mass budget of the galactic halo, there have been several other contributions that argue that these white dwarfs are not genuine halo members but, instead, thick-disc stars. We show here that the interpretation of this sample is based on the adopted distances, which are obtained from a colour–magnitude calibration, and we demonstrate that when the correct distances are used a sizeable fraction of these putative halo white dwarfs belong indeed to the disc population. We also perform a maximum likelihood analysis of the remaining set of white dwarfs and we find that they most probably belong to the thick-disc population. However, another possible explanation is that this sample of white dwarfs has been drawn from a 1:1 mixture of the halo and disc white dwarf populations.Monthly Notices of the Royal Astronomical Society 10/2002; 336(3):971 - 978. · 4.90 Impact Factor -
Article: Monte Carlo simulations of the disc white dwarf population
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ABSTRACT: In order to understand the dynamical and chemical evolution of our Galaxy it is of fundamental importance to study the local neighbourhood. White dwarf stars are ideal candidates to probe the history of the solar neighbourhood, since these `fossil' stars have very long evolutionary time-scales and, at the same time, their evolution is relatively well understood. In fact, the white dwarf luminosity function has been used for this purpose by several authors. However, a long-standing problem arises from the relatively poor statistics of the samples, especially at low luminosities. In this paper we assess the statistical reliability of the white dwarf luminosity function by using a Monte Carlo approach.Monthly Notices of the Royal Astronomical Society 12/1998; 302(1):173 - 188. · 4.90 Impact Factor -
Article: Neural Network identification of halo white dwarfs
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ABSTRACT: The white dwarf luminosity function has proven to be an excellent tool to study some properties of the galactic disk such as its age and the past history of the local star formation rate. The existence of an observational luminosity function for halo white dwarfs could provide valuable information about its age, the time that the star formation rate lasted, and could also constrain the shape of the allowed Initial Mass Functions (IMF). However, the main problem is the scarce number of white dwarfs already identified as halo stars. In this Letter we show how an artificial intelligence algorithm can be succesfully used to classify the population of spectroscopically identified white dwarfs allowing us to identify several potential halo white dwarfs and to improve the significance of its luminosity function. Comment: 15 pages, 3 postscript figures. Accepted for publication in ApJ Letters, uses aasms4.sty09/1998; -
Article: Using self-organizing maps to identify potential halo white dwarfs.
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ABSTRACT: We present the results of an unsupervised classification of the disk and halo white dwarf populations in the solar neighborhood. The classification is done by merging the results of detailed Monte Carlo (MC) simulations, which reproduce very well the characteristics of the white dwarf populations in the solar neighborhood, with a catalogue of real stars. The resulting composite catalogue is analyzed using a competitive learning algorithm. In particular we have used the so-called self-organized map. The MC simulated stars are used as tracers and help in identifying the resulting clusters. The results of such an strategy turn out to be quite satisfactory, suggesting that this approach can provide an useful framework for analyzing large databases of white dwarfs with well determined kinematical, spatial and photometric properties once they become available in the next decade. Moreover, the results are of astrophysical interest as well, since a straightforward interpretation of several recent astronomical observations, like the detected microlensing events in the direction of the Magellanic Clouds, the possible detection of high proper motion white dwarfs in the Hubble Deep Field and the discovery of high velocity white dwarfs in the solar neighborhood, suggests that a fraction of the baryonic dark matter component of our galaxy could be in the form of old and dim halo white dwarfs.Neural Networks 16(3-4):405-10. · 2.18 Impact Factor -
Article: A white dwarf cooling age of 8[thinsp]Gyr for NGC 6791 from physical separation processes
Nature 465(7295):194-196. · 36.28 Impact Factor
Top co-authors
Top Journals
Institutions
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1998–2010
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Polytechnic University of Catalonia
- Department of Applied Physics (FA)
Barcelona, Catalonia, Spain
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2007
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Spanish National Research Council
- Institute of Space Sciences
Madrid, Madrid, Spain
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2006
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IEEC Institute of Space Studies of Catalonia
Barcelona, Catalonia, Spain
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2002
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Institut de Ciències de l'Espai
Sabadell, Catalonia, Spain
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