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  • Monte Carlo Simulations of the Population of Single and Binary White Dwarfs of our Galaxy  Open access

     Camacho Díaz, Judit
    Defense's date: 2014-06-19
    Universitat Politècnica de Catalunya
    Theses

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    Degut a que les nanes blanques són l'etapa final de l'evolució de la gran majoria de les estrelles, aporten informació molt important sobre l'evolució química de la nostra galàxia, la taxa de formació d'estrelles, i la seva estructura i dinàmica. En aquesta tesi es presta atenció a dos problemes astrofísics relacionats tot i que diferents que involucren les nanes blanques.El primer d'aquests problemes es refereix a la naturalesa i la real ubicació dels successos de microlents en la direcció del Gran Núvols de Magallanes (LMC) que continua essent un misteri. Els principals grups d'observació, MACHO i EROS, es troben en disputa entre si, tot i que s'ha aconseguit cert consens en els punts més importants.El segon dels problemes que abordem en aquesta tesi és també un problema obert. Els sistemes binaris compactes representen el punt clau de diversos fenòmens interessants en la nostra galàxia i en altres galàxies. De fet, la gran majoria de binàries compactes es formen a través d'almenys un episodi d'embolcall comú. Tot i que els conceptes bàsics de l'evolució durant la fase d'embolcall comú són més aviat simples, els detalls encara estan lluny de ser ben entesos.Per aclarir aquests problemes, s'ha utilitzat un simulador Monte Carlo ja existent. Hem ampliat aquest simulador incloent-hi els models més recents de refredament de nanes blanques, així com un model detallat de la nostra galàxia i del LMC per tal d'emular els experiments dels equips MACHO i EROS. A més, s'ha inclòs la població de nanes vermelles i s'ha realitzat una anàlisi conjunta de les aportacions d'ambdues poblacions al contingut total de matèria fosca de la nostra galàxia. D'altra banda, s'ha estudiat la contribució de la subpoblació de nanes blanques amb atmosferes d'hidrogen deficient .D'altra banda, el nostre codi de Monte Carlo s'ha ampliat per analitzar els sistemes compostos per una nana blanca i un estel de la seqüència principal que han evolucionat a través d'una fase d'embolcall comú. S'ha implementat de forma detallada diversos processos físics, incloent-hi una descripció completa de l'episodi de transferència de massa, un tractament complet de l'episodi de desbordament del lòbul de Roche, marees gravitacionals i l'evolució orbital del sistema binari. Així mateix, hem inclòs detalladament tots els diferents criteris de selecció i biaixos observacionals.Els resultats de les nostres simulacions de Monte Carlo dels experiments de microlents mostren un bon acord amb els resultats dels equips EROS i MACHO. Les nostres troballes mostren que ni les nanes blanques ni les nanes vermelles poden ser els principals contribuents a la profunditat òptica dels microlents en la direcció de la LMC. Aquests fets reforcen la idea, prèviament assenyalada per altres estudis, que la profunditat òptica trobada per l'equip MACHO és molt probablement una sobreestimació, potser a causa de la contaminació de microlents de la pròpia LMC, entre d'altres possibles explicacions .Pel que fa al segon punt d'aquesta tesi, les nostres simulacions Monte Carlo reprodueixen correctament les propietats de la població de WD + MS PCEBs. El millor ajust s'obté per models amb fraccions de l'energia interna inferiors al ~20% , i valors per al paràmetre d'eficiència de l'embolcall comú inferiors a ~0,3.En conclusió , el treball presentat en aquesta tesi suposa un important pas endavant no només en la limitació de la naturalesa dels descobriments de microlents , sinó també en la validació dels models per a les poblacions de nanes blanques observades de la nostra Galàxia. Per no esmentar el fet que posa les bases per a moltes altres missions en curs i previstes , i com ajuda als observadors en les seves prediccions.

    Since white dwarfs are the final stage of the evolution of the vast majority of stars, they carry important information about the chemical evolution of our Galaxy, its star formation rate, and its structure and dynamics. This thesis pays attention to two related but distinct astrophysical problems involving white dwarfs. The first of these problems concern the nature and the location of the microlensing events towards the Large Magellanic Clouds (LMC), which still remains a mystery. The main observational groups, MACHO and EROS, are in dispute each, yet agreement has now been reached in some of the most important points. The second of the problems we address in this thesis is an open problem as well. Close compact binaries are at the heart of several interesting phenomena in our Galaxy as well. Close compact binaries are formed through at least one common envelope episode. Even though the basics concepts of the evolution during a common envelope phase are rather simple, the details are still far from being well understood. To shed light on these problems, we used an existing Monte Carlo simulator. We expanded this simulator integrating the most up-to-date white dwarfs cooling models as well as detailed modeling of our Galaxy and the LMC in order to mimic both the MACHO and EROS experiments. Additionally, we included the red dwarf population and performed a joint analysis of the contributions of both populations to the dark matter content of our Galaxy. Moreover, we studied the contribution of the subpopulation of white dwarfs with hydrogen-deficient atmospheres. On the other hand, our Monte Carlo code has been expanded to deal with those systems composed by a white dwarf and a main sequence star, which have evolved through a common episode. A detailed implementation of several different physical processes, including a full description of the mass transfer episode, a complete treatment of the Roche lobe overflow episode, gravitational tides and orbital evolution of the binary system, was performed. Furthermore, in our treatment we carefully included all the different selection criteria and observational biases. This allowed us to make a meaningful comparison with the available data, besides examining the role played by the binding energy parameter and by the common envelope parameter, not to mention the role played by the distribution of secondary masses of the binary systems. The results of our Monte Carlo simulations of the microlensing experiments show agreement with the findings of the EROS and MACHO survey. Our findings show that neither white dwarfs nor red dwarfs can be major contributors to the microlensing depth towards the LMC. These facts reinforce the idea, previously pointed by others studies, that the optical depth found by the MACHO survey is highly likely an overestimate, probably due to contamination of self-lensing objects, amid other possible explanations. Concerning the second point of this thesis, our Monte Carlo simulations correctly reproduce the properties of the observed population of post-common envelope white dwarf plus main sequence binaries, once biases are taken into account. The best-fit models are obtained with fractions less than ~20% of the internal energy contributing to the ejection of the star progenitor¿s envelope, and values for the common-envelope efficiency parameter less than ~0.3. To conclude, the work presented in this thesis poses an important step forward not only in constraining the microlensing discoveries, but also in validating models for the observed white-dwarf populations of our Galaxy.

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    A population synthesis study of the luminosity function of hot white dwarfs  Open access

     Torres Gil, Santiago; Garcia-berro Montilla, Enrique; Krzesinski, Jurek; Kleinman, Scot J.
    Astronomy and astrophysics
    Date of publication: 2014-03-05
    Journal article

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    Context. We present a coherent and detailed Monte Carlo simulation of the population of hot white dwarfs. We assess the statistical significance of the hot end of the white dwarf luminosity function and the role played by the bolometric corrections of hydrogen-rich white dwarfs at high effective temperatures. Aims. We use the most up-to-date stellar evolutionary models and implement a full description of the observational selection biases to obtain realistic simulations of the observed white dwarf population. Methods. Our theoretical results are compared with the luminosity function of hot white dwarfs obtained from the Sloan Digital Sky Survey (SDSS), for both DA and non-DA white dwarfs. Results. We find that the theoretical results are in excellent agreement with the observational data for the population of white dwarfs with hydrogen deficient atmospheres (non-DA white dwarfs). For the population of white dwarfs with hydrogen-rich atmospheres (white dwarfs of the DA class), our simulations show some discrepancies with the observations for the brightest luminosity bins, namely those corresponding to luminosities larger than ~10 L.These discrepancies can be attributed to the way in which the masses of the white dwarfs contributing to this luminosity bin have been computed, as most of them have masses smaller than the theoretical lower limit for carbon-oxygen white dwarfs. Conclusions. We conclude that the way in which the observational luminosity function of hot white dwarfs is obtained is very sensitive to the particular implementation of the method used to derive the masses of the sample. We also provide a revised luminosity function for hot white dwarfs with hydrogen-rich atmospheres. © ESO, 2014.

    Context. We present a coherent and detailed Monte Carlo simulation of the population of hot white dwarfs. We assess the statistical significance of the hot end of the white dwarf luminosity function and the role played by the bolometric corrections of hydrogen-rich white dwarfs at high effective temperatures. Aims. We use the most up-to-date stellar evolutionary models and implement a full description of the observational selection biases to obtain realistic simulations of the observed white dwarf population. Methods. Our theoretical results are compared with the luminosity function of hot white dwarfs obtained from the Sloan Digital Sky Survey (SDSS), for both DA and non-DA white dwarfs. Results. We find that the theoretical results are in excellent agreement with the observational data for the population of white dwarfs with hydrogen deficient atmospheres (non-DA white dwarfs). For the population of white dwarfs with hydrogen-rich atmospheres (white dwarfs of the DA class), our simulations show some discrepancies with the observations for the brightest luminosity bins, namely those corresponding to luminosities larger than ~10 L.These discrepancies can be attributed to the way in which the masses of the white dwarfs contributing to this luminosity bin have been computed, as most of them have masses smaller than the theoretical lower limit for carbon-oxygen white dwarfs. Conclusions. We conclude that the way in which the observational luminosity function of hot white dwarfs is obtained is very sensitive to the particular implementation of the method used to derive the masses of the sample. We also provide a revised luminosity function for hot white dwarfs with hydrogen-rich atmospheres. © ESO, 2014.

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    The effects of metallicity on the Galactic disk population of white dwarfs  Open access

     Cojocaru, Elena Ruxandra; Torres Gil, Santiago; Isern Vilaboy, Jordi; Garcia-berro Montilla, Enrique
    Astronomy and astrophysics
    Date of publication: 2014-06
    Journal article

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    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 atmospheres for both carbon-oxygen and oxygen-neon cores. We use two different models to assess the evolution of the metallicity: the first, where the adopted metallicity is constant with time but with a moderate dispersion, and the second where the metallicity increases with time. Results. We found that our theoretical results are in a very satisfactory agreement with the observational luminosity functions obtained from the Sloan Digital Sky Survey (SDSS) and from the SuperCOSMOS Sky Survey (SSS). These results are independent of the adopted age-metallicity law. In particular, we found that the age-metallicity law has no noticeable impact in shaping the bright branch of the white dwarf luminosity function and that the position of its cut-off is almost insensitive to the adopted age-metallicity relationship. Conclusions. Because the shape of the bright branch of the white dwarf luminosity function is insensitive to the age-metallicity law, it can be safely employed to test the theoretical evolutionary sequences, while its location provides a robust indicator of the age of the Galactic disk due to the limited sensitivity of the position of the drop-off to the distribution of metallicities.

    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 atmospheres for both carbon-oxygen and oxygen-neon cores. We use two different models to assess the evolution of the metallicity: the first, where the adopted metallicity is constant with time but with a moderate dispersion, and the second where the metallicity increases with time. Results. We found that our theoretical results are in a very satisfactory agreement with the observational luminosity functions obtained from the Sloan Digital Sky Survey (SDSS) and from the SuperCOSMOS Sky Survey (SSS). These results are independent of the adopted age-metallicity law. In particular, we found that the age-metallicity law has no noticeable impact in shaping the bright branch of the white dwarf luminosity function and that the position of its cut-off is almost insensitive to the adopted age-metallicity relationship. Conclusions. Because the shape of the bright branch of the white dwarf luminosity function is insensitive to the age-metallicity law, it can be safely employed to test the theoretical evolutionary sequences, while its location provides a robust indicator of the age of the Galactic disk due to the limited sensitivity of the position of the drop-off to the distribution of metallicities

  • Explaining the Type Ia supernova PTF 11kx with a violent prompt merger scenario

     Garcia-berro Montilla, Enrique; Torres Gil, Santiago; Camacho Diaz, Judit; Soker, Noam; Kashi, Amit
    Monthly notices of the Royal Astronomical Society
    Date of publication: 2013-05
    Journal article

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    We argue that the multiple shells of circumstellar material (CSM) and the supernovae (SNe) ejecta interaction with the CSM starting 59 d after the explosion of the Type Ia SN 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 white dwarf (WD) companion with the hot core of a massive asymptotic giant branch star. In most cases, the WD is disrupted and accreted on to 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 on to 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 similar to 1000 au of the exploding PTF 11kx star, for the presence of hydrogen, and for the presence of shells in the CSM.

  • Enanas blancas: progenitores, evolución, pulsaciones y explosiones

     Diaz Aguiló, Marc; Renedo Rouco, Isabel; Sala Cladellas, Gloria; Escartin Vigo, Jose Antonio; Loren Aguilar, Pablo; Garcia Senz, Domingo; Torres Gil, Santiago; Camacho Díaz, Judit; Garcia-berro Montilla, Enrique
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  • Monte Carlo simulations of the luminosity function of hot white dwarfs

     Torres Gil, Santiago; Garcia-berro Montilla, Enrique; Krzesinski, Jurek; Kleinman, Scot J.
    European White Dwarf Workshop
    Presentation's date: 2012-08
    Presentation of work at congresses

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    We present a detailed Monte Carlo simulation of the population of the hot branch of the white dwarf luminosity function. We used the most up-to-date stellar evolutionary models and we implemented a full description of the observational selection biases. Our theoretical results are compared with the luminosity function of hot white dwarfs obtained from the Sloan Digital Sky Survey (SDSS), for both DA and non-DA white dwarfs. For non-DA white dwarfs we find an excellent agreement with the observational data, while for DA white dwarfs our simulations show some discrepancies with the observations for the brightest luminosity bins, those corresponding to L greater than or similar to 10 L-circle dot.

  • An upper limit to the secular variation of the gravitational constant from white dwarf stars

     Garcia-berro Montilla, Enrique; Loren Aguilar, Pablo; Torres Gil, Santiago; Althaus, Leandro G.; Isern Vilaboy, Jordi
    Journal of cosmology and astroparticle physics
    Date of publication: 2011-05
    Journal article

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  • The Cooling of White Dwarfs and a Varying Gravitational Constant

     Garcia-berro Montilla, Enrique; Althaus, Leandro G.; Torres Gil, Santiago; Loren Aguilar, Pablo; Corsico, Alejandro H.; Isern Vilaboy, Jordi
    Astrophysics and space science proceedings
    Date of publication: 2011
    Journal article

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  • The evolution of white dwarfs with a varying gravitational constant

     Althaus, Leandro G.; Corsico, Alejandro H.; Torres Gil, Santiago; Loren Aguilar, Pablo; Isern Vilaboy, Jordi; Garcia-berro Montilla, Enrique
    Astronomy and astrophysics
    Date of publication: 2011-03
    Journal article

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  • Double degenerate mergers as progenitors of high-field magnetic white dwarfs

     Garcia-berro Montilla, Enrique; Loren Aguilar, Pablo; Aznar Siguan, Gabriela; Torres Gil, Santiago; Camacho Díaz, Judit; Althaus, Leandro G.; Córsico, Alejando Hugo; Kulebi, Baybar; Isern Vilaboy, Jordi
    Astrophysical journal
    Date of publication: 2011-04-10
    Journal article

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    The white-dwarf cooling sequence of NGC 6791: a unique tool for stellar evolution  Open access

     Garcia-berro Montilla, Enrique; Torres Gil, Santiago; Renedo Rouco, Isabel; Camacho Díaz, Judit; Althaus, Leandro G.; Córsico, Alejandro H.; Salaris, Mauricio; Isern Vilaboy, Jordi
    Astronomy and astrophysics
    Date of publication: 2011-09
    Journal article

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    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 of white dwarfs to disclose the presence of cluster subpopulations with a different initial chemical composition, and we obtain an upper bound to the fraction of hydrogen-deficient white dwarfs. Methods. We use a Monte Carlo simulator that employs up-to-date evolutionary cooling sequences for white dwarfs with hydrogenrich and hydrogen-deficient atmospheres, with carbon-oxygen and helium cores. The cooling sequences for carbon-oxygen cores account for the delays introduced by both 22Ne sedimentation in the liquid phase and by carbon-oxygen phase separation upon crystallization. Results. We do not find evidence for a substantial fraction of helium-core white dwarfs, and hence our results support the suggestion that the origin of the bright peak of the white-dwarf luminosity function can only be attributed to a population of unresolved binary white dwarfs. Moreover, our results indicate that if this hypothesis is at the origin of the bright peak, the number distribution of secondary masses of the population of unresolved binaries has to increase with increasing mass ratio between the secondary and primary components of the progenitor system. We also find that the observed cooling sequence appears to be able to constrain the presence of progenitor subpopulations with different chemical compositions and the fraction of hydrogen-deficient white dwarfs. Conclusions. Our simulations place interesting constraints on important characteristics of the stellar populations of NGC 6791. In particular, we find that the fraction of single helium-core white dwarfs must be smaller than 5%, that a subpopulation of stars with zero metallicity must be <∼12%, while if the adopted metallicity of the subpopulation is solar the upper limit is ∼8%. Finally, we also find that the fraction of hydrogen-deficient white dwarfs in this particular cluster is surprinsingly small (<∼6%).

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

     Torres Gil, Santiago; Camacho Díaz, Judit; Rebassa-Mansergas, Alberto; Zorotovic, Monica; Schreiber, Mathias R.; Garcia-berro Montilla, Enrique
    Evolution of Compact Binaries
    Presentation's date: 2011-05-06
    Presentation of work at congresses

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  • The white dwarf population of tri-axial haloes

     Torres Gil, Santiago; Camacho Díaz, Judit; Garcia-berro Montilla, Enrique
    Date of publication: 2010
    Book chapter

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

     Camacho Díaz, Judit; Torres Gil, Santiago; Garcia-berro Montilla, Enrique; Zorotovic, Mónica; Schreiber, Mathias R.
    Date of publication: 2010
    Book chapter

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  • The effects of the observational selection criteria on the post-common envelope white dwarf-main sequence binary population

     Camacho Díaz, Judit; Torres Gil, Santiago; Garcia-berro Montilla, Enrique; Zorotovic, Monica; Schreiber, Mathias R.; Rebassa-Mansergas Mansergas, Alberto
    Date of publication: 2010
    Book chapter

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  • White dwarfs with hydrogen-deficient atmospheres and the dark matter content of the Galaxy

     Torres Gil, Santiago; Camacho Díaz, Judit; Isern Vilaboy, Jordi; Garcia-berro Montilla, Enrique
    Astronomy and astrophysics
    Date of publication: 2010-02
    Journal article

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

     Camacho Díaz, Judit; Torres Gil, Santiago; Garcia-berro Montilla, Enrique; Zorotovic, Monica; Schreiber, Mathias R.
    AIP Conference proceedings
    Date of publication: 2010
    Journal article

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  • A white dwarf cooling age of 8 Gyr for NGC 6791 from physical separation processes

     Garcia-berro Montilla, Enrique; Torres Gil, Santiago; Althaus, Leandro Gabriel; Renedo Rouco, Isabel; Loren Aguilar, Pablo; Corsico, Alejandro H.; Rohrmann, Rene Daniel; Salaris, Mauricio; Isern Vilaboy, Jordi
    Nature
    Date of publication: 2010-05-13
    Journal article

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  • Physics of compact objects: I.Theorical modeling and observations of stellar explosions

     Casanova Bustamante, Jordi; Loren Aguilar, Pablo; Camacho Díaz, Judit; Sala Cladellas, Gloria; Renedo Rouco, Isabel; Garcia-berro Montilla, Enrique; Bravo Guil, Eduardo; Garcia Senz, Domingo; Torres Gil, Santiago; Longland, Richard Leigh; Parikh, Anuj Ramesh; José Pont, Jordi
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  • Physics of Compact Objects: explosive nucleosynthesis and evolution

     José Pont, Jordi; Camacho Díaz, Judit; Torres Gil, Santiago; Renedo Rouco, Isabel; Garcia Senz, Domingo; Sala Cladellas, Gloria; Casanova Bustamante, Jordi; Garcia-berro Montilla, Enrique
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    The effects of the Observational Selection Criteria on the post common envelope white dwarf-main sequence binary population  Open access

     Camacho Díaz, Judit; Torres Gil, Santiago; Garcia-berro Montilla, Enrique; Zorotovic, Mónica; Schreiber, Mathias R.; Rebassa-Mansergas, Alberto
    17th European Workshop on White Dwarfs
    Presentation's date: 2010
    Presentation of work at congresses

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    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

  • Study of binary systems after a common envelope episode

     Torres Gil, Santiago; Camacho Díaz, Judit; Zorotovic, Monica; Schreiber, Mathias R.
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  • The white dwarf cooling age of NGC 6791

     Garcia-berro Montilla, Enrique; Althaus, Leandro G.; Torres Gil, Santiago; Loren Aguilar, Pablo; Renedo Rouco, Isabel; Corsico, Alejandro H.; Isern Vilaboy, Jordi; Salaris, Maurizio; Rohrmann, Rene Daniel
    European White Dwarf Workshop
    Presentation's date: 2010-08
    Presentation of work at congresses

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  • The white dwarf population of tri-axial haloes

     Torres Gil, Santiago; Camacho Díaz, Judit; Garcia-berro Montilla, Enrique
    European White Dwarf Workshop
    Presentation's date: 2010
    Presentation of work at congresses

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    Monte Carlo simulations of the post-common envelope white dwarf-main sequence binary population  Open access

     Camacho Díaz, Judit; Torres Gil, Santiago; Garcia-berro Montilla, Enrique; Zorotovic, Monica; Schreiber, Mathias R.
    International Conference on Binaries: in celebration of Ron Webbink's 65th birthday
    Presentation's date: 2010-06
    Presentation of work at congresses

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  • White dwarfs, red dwarfs and halo dark matter

     Garcia-berro Montilla, Enrique; Torres Gil, Santiago; Camacho Díaz, Judit; Isern Vilaboy, Jorge
    Journal of physics: conference series
    Date of publication: 2009
    Journal article

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    The nature of the microlensing events observed by the MACHO team towards the LMC still remains controversial. Low-mass substellar objects and stars with masses larger than ~ 1M¿ have been ruled out, while stars of ~ 0.5 M¿ are the most probable candidates. This means that the microlenses should be either red or white dwarfs. Consequently, we assess jointly the relative contributions of both types of stars to the mass budget of the Galactic halo. We use a Monte Carlo code that incorporates up-to-date evolutionary sequences of both red dwarfs and white dwarfs as well as detailed descriptions of both our Galaxy and the LMC and we compare the synthetic populations obtained with our simulator with the results obtained by the MACHO and EROS experiments. We find that the contribution of the red dwarf population is not enough to explain the number of events measured by the MACHO team. Even though, the optical depth obtained in our simulations almost doubles that obtained when taking into account the white dwarf population alone. Finally, we also find that the contribution to the halo dark matter of the entire population under study is smaller than 10%, at the 95% confidence level.

  • On the origin of white dwarfs with carbon-dominated atmospheres: the case of H1504+65

     Althaus, Lg; Corsico, Ah; Torres Gil, Santiago; Garcia-berro Montilla, Enrique
    Astronomy and astrophysics
    Date of publication: 2009-02
    Journal article

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    Monte Carlo simulations of the binary white dwarf population: a progress report  Open access

     Camacho Díaz, Judit; Torres Gil, Santiago; Garcia-berro Montilla, Enrique
    Journal of physics: conference series
    Date of publication: 2009
    Journal article

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    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.

  • Axions and the white dwarf luminosity function

     Isern Vilaboy, Jorge; Catalán Ruiz, Silvia; Garcia-berro Montilla, Enrique; Torres Gil, Santiago
    Journal of physics: conference series
    Date of publication: 2009-06-01
    Journal article

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  • Astronomy and Astrophysics, Consolidated Research Group

     Garcia-berro Montilla, Enrique; Camacho Díaz, Judit; Torres Gil, Santiago
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  • Two challenges for modern stellar evolution: supernova progenitors and AGB stars

     Garcia-berro Montilla, Enrique; Camacho Díaz, Judit; Torres Gil, Santiago
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  • DOS RETOS PARA LA EVOLUCION ESTELAR MODERNA:PROGENITORES DE SUPERNOVA Y ESTRELLAS AGB

     Casanova Bustamante, Jordi; Cabezón Gómez, Rubén Martín; Garcia Senz, Domingo; Torres Gil, Santiago; Renedo Rouco, Isabel; Loren Aguilar, Pablo; Camacho Díaz, Judit; Sala Cladellas, Gloria; Escartin Vigo, Jose Antonio; González Villafranca, Alberto; Garcia-berro Montilla, Enrique
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  • GRUP D'ASTRONOMIA I ASTROFÍSICA

     Torres Gil, Santiago; Renedo Rouco, Isabel; González Villafranca, Alberto; Bravo Guil, Eduardo; Cabezón Gómez, Rubén Martín; Garcia Senz, Domingo; Diaz Aguiló, Marc; José Pont, Jordi; Riera Mora, M. Angeles; Loren Aguilar, Pablo; Camacho Díaz, Judit; Sala Cladellas, Gloria; Escartin Vigo, Jose Antonio; Casanova Bustamante, Jordi; Garcia-berro Montilla, Enrique
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  • Análisis de la aplicación de nuevas metodologias docentes en ingenieria

     Bruna Escuer, Pere; Calvete Manrique, Daniel; Crespo Artiaga, Daniel; Pilar, Gil; Gutierrez, Jordi; Torres Gil, Santiago; Alonso Maleta, Maria Aranzazu
    VI Taller Iberoamericano de Educación en Ciencia e Ingeniería de Materiales (TIECIM)
    Presentation's date: 2008-12-02
    Presentation of work at congresses

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    Monte Carlo simulations of the binary white dwarf population: a progress report  Open access

     Camacho Díaz, Judit; Torres Gil, Santiago; Garcia-berro Montilla, Enrique
    16th European White Dwarfs Workshop
    Presentation's date: 2008-06
    Presentation of work at congresses

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    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.

  • White dwarfs, red dwarfs and halo dark matter

     Garcia-berro Montilla, Enrique; Torres Gil, Santiago; Camacho Díaz, Judit; Isern Vilaboy, Jorge
    16th European White Dwarfs Workshop
    Presentation's date: 2008
    Presentation of work at congresses

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  • Axions and the cooling of white dwarfs stars

     Garcia-berro Montilla, Enrique; Torres Gil, Santiago
    Astrophysical journal
    Date of publication: 2008-01
    Journal article

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    The contribution of red dwarfs and white dwarfs to the halo dark matter  Open access

     Torres Gil, Santiago; Camacho Díaz, Judit; Isern Vilaboy, Jordi; Garcia-berro Montilla, Enrique
    Astronomy and astrophysics
    Date of publication: 2008
    Journal article

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

     Camacho Díaz, Judit; Torres Gil, Santiago; Garcia-berro Montilla, Enrique
    Date of publication: 2007
    Book chapter

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    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

  • Monte Carlo simulations of the Galactic binary population. Monte Carlo simulations of the formation channels of SNeIb

     Camacho Díaz, Judit; Torres Gil, Santiago; Garcia-berro Montilla, Enrique
    Supernovae: lights in the darkness (XXIII trobades Científiques de la Mediterrània)
    Presentation's date: 2007-08
    Presentation of work at congresses

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    The contribution of Oxygen-Neon white dwarfs to the MACHO content of the Galactic halo  Open access

     Camacho Díaz, Judit; Torres Gil, Santiago; Villaboy, Isern J; Althaus, L; Garcia-berro Montilla, Enrique
    Astronomy and astrophysics
    Date of publication: 2007-08
    Journal article

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    Context. The interpretation of microlensing results towards the Large Magellanic Cloud (LMC) still remains controversial. White dwarfs have been proposed to explain these results and, hence, to contribute significantly to the mass budget of our Galaxy. However, several constraints on the role played by regular carbon-oxygen white dwarfs exist. Aims. Massive white dwarfs are thought to be made of a mixture of oxygen and neon. Correspondingly, their cooling rate is larger than those of typical carbon-oxygen white dwarfs and they fade to invisibility in short timescales. Consequently, they constitute a good candidate for explaining the microlensing results. Methods. Here, we examine in detail this hypothesis by using the most recent and up-to-date cooling tracks for massive white dwarfs and a Monte Carlo simulator which takes into account the most relevant Galactic inputs. Results.We find that oxygen-neon white dwarfs cannot account for a substantial fraction of the microlensing depth towards the LMC,independently of the adopted initial mass function, although some microlensing events could be due to oxygen-neon white dwarfs. Conclusions.The white dwarf population contributes at most a 5% to the mass of the Galactic halo.

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    The white dwarf luminosity function - II. The effect of the measurement errors and other biases  Open access

     Torres Gil, Santiago; Garcia-berro Montilla, Enrique; Isern Vilaboy, Jordi
    Monthly notices of the Royal Astronomical Society
    Date of publication: 2007-07
    Journal article

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    Context. The interpretation of microlensing results towards the Large Magellanic Cloud (LMC) still remains controversial. White dwarfs have been proposed to explain these results and, hence, to contribute significantly to the mass budget of our Galaxy. However, several constraints on the role played by regular carbon-oxygen white dwarfs exist. Aims. Massive white dwarfs are thought to be made of a mixture of oxygen and neon. Correspondingly, their cooling rate is larger than those of typical carbon-oxygen white dwarfs and they fade to invisibility in short timescales. Consequently, they constitute a good candidate for explaining the microlensing results. Methods. Here, we examine in detail this hypothesis by using the most recent and up-to-date cooling tracks for massive white dwarfs and a Monte Carlo simulator which takes into account the most relevant Galactic inputs. Results.We find that oxygen-neon white dwarfs cannot account for a substantial fraction of the microlensing depth towards the LMC,independently of the adopted initial mass function, although some microlensing events could be due to oxygen-neon white dwarfs. Conclusions.The white dwarf population contributes at most a 5% to the mass of the Galactic halo.

  • The white dwarf luminosity function: measurement errors and estimators

     Torres Gil, Santiago; Garcia-berro Montilla, Enrique
    15th European Workshop on White Dwarfs
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    The white dwarf luminosity function . I. Statistical errors and alternatives  Open access

     Geijo, E M; Torres Gil, Santiago; Vilaboy, Isern I J; Garcia-berro Montilla, Enrique
    Monthly notices of the Royal Astronomical Society
    Date of publication: 2006-07
    Journal article

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    The white dwarf luminosity function is an important tool for the study of the solar neighbourhood, since it allows the determination of the age of the Galactic disc. Over the years, several methods have been proposed to compute galaxy luminosity functions, from the most simple ones – counting sample objects inside a given volume – to very sophisticated ones – like the C- method, the STY method or the Choloniewski method, among others. However, only the 1/Vmax method is usually employed in computing the white dwarf luminosity function and other methods have not been applied so far to the observational sample of spectroscopically identified white dwarfs – in sharp contrast with the situation when galaxy luminosity functions are derived from a large variety of samples. Moreover, the statistical significance of the white dwarf luminosity function has also received little attention and a thorough study still remains to be done. In this paper, we study, using a controlled synthetic sample of white dwarfs generated using a Monte Carlo simulator, which is the statistical significance of the white dwarf luminosity function and which are the expected biases. We also present a comparison between different estimators for computing the white dwarf luminosity function. We find that for sample sizes large enough the 1/Vmax method provides a reliable characterization of the white dwarf luminosity function, provided that the input sample is selected carefully. Particularly, the 1/Vmax method recovers well the position of the cut-off of the white dwarf luminosity function. However, this method turns out to be less robust than the Choloniewski method when the possible incompletenesses of the sample are taken into account. We also find that the Choloniewski method performs better than the method in estimating the overall density of white dwarfs, but misses the exact location of the cut-off of the white dwarf luminosity function.

  • The Late stages of stellar evolution : stellar explosions and non-interacting white dwarfs in the UV

     Hernanz Carbó, Margarita; Dominguez, I.; Garcia-berro Montilla, Enrique; Garcia Senz, Domingo; Barstow, M.A.; Bravo Guil, Eduardo; Gonzalez-Riestra, R.; Isern, J.; José Pont, Jordi; Torres Gil, Santiago
    Date of publication: 2006-12
    Book chapter

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  • Las poblaciones fósiles de la galaxia: progenitores, propiedades y aplicaciones.

     Garcia-berro Montilla, Enrique; Torres Gil, Santiago; Bravo Guil, Eduardo
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  • Ayudas de investigación a grupos consolidados de la Generalitat de Catalunya

     Garcia-berro Montilla, Enrique; Torres Gil, Santiago
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  • Simulating Gaia performances on white dwarfs

     Torres Gil, Santiago; Garcia-berro Montilla, Enrique
    Monthly notices of the Royal Astronomical Society
    Date of publication: 2005-05
    Journal article

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