Pulsating White Dwarfs
Asteroseismology of white dwarfs with fully evolutionary models Alejandra D. Romero, Alejandro H. Córsico, Leandro G. Althaus, & Marcelo M. Miller Bertolami Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Argentina acorsico@fcaglp.unlp.edu.ar
White dwarf asteroseismology fully exploits the comparison between the observed pulsation periods in white dwarf stars and the periods computed for appropriate theoretical models. It allows us to infer details of the origin, internal structure and evolution of these old and compact stars. In this work, we present the results of an asteroseismological analysis of ZZ Ceti (or DAV) stars and V777 Her (or DBV) stars on the basis of a new set of fully evolutionary DA (H- rich envelope) and DB (He- rich envelope) white dwarf models characterized by detailed chemical profiles from the centre to the surface. This is the first work aimed at an asteroseismological analysis of DAV and DBV stars that employs evolutionary white dwarf models computed from the ZAMS through the thermally pulsing and mass loss phases on the AGB, the domain of planetary nebulae, and finally the white dwaf stage. We perform a kind of "ensemble asteroseismology" on a large set of DAV stars, an approach that provides for the first time, valuable information about the distribution of H envelope thicknesses of DA white dwarfs. Among the targets of our study, we include also the recently discovered DAV star WD J191643.83+393849.7 (Hermes et al. 2011) and DBV star KIC 8626021 ({\O}stensen et al. 2011) located in the field of view of the Kepler Mission.
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Theoretical seismic properties of low-mass white dwarfs: first results Alejandro H. Córsico, Alejandra D. Romero, Leandro G. Althaus, & J. J. Hermes Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Argentina acorsico@fcaglp.unlp.edu.ar
In recent years, many low-mass ($\lesssim 0.45 M_{\odot}$) white-dwarf stars supposed to harbour cores made of He have been detected in the field of the Milky Way and in several galactic globular and open clusters. Until recently, no objects of this kind showed photometric variability. This situation has changed recently with the exciting discovery of SDSS J184037.78+642312.3, the first pulsating low-mass white-dwarf star. Motivated by this extremely important finding, and in view of the very valuable asteroseismological potential of these objects, we present here a detailed adiabatic and nonadiabatic pulsational study applied to low-mass He-core white dwarfs with masses ranging from $0.17$ to $0.46 M_{\odot}$, based on full evolutionary models representative of these objects. This study is aimed to provide a theoretical basis from which to interpret future observations of variable low-mass white dwarfs.
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An Analytical Phase-Centric Approach to O-C Analysis James Dalessio (1), Judith L. Provencal (1), Harry L. Shipman (1), Brad N. Barlow (2) 1: Department of Physics and Astronomy, University of Delaware; 2: Department of Astronomy and Astrophysics, The Pennsylvania State University, United States dalessio.james@gmail.com
The O-C (observed minus calculated) method is a fundamental tool for time domain astronomy. Much of the existing O-C formalism focuses on long period variations and discreet observations of times of maximum light. We produce phase-centric formalism more appropriate for short period variables like white dwarfs and derive an analytical model for O-C under all combinations of frequency and signal travel time variation. We also investigate degenerate terms in the analytical model and discuss some pitfalls of white dwarf O-C analysis.
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New insights on the asteroseismological study of R548 Noemi Giammichele University of Montreal, Canada noemi@astro.umontreal.ca
We present a complete asteroseismological study of the pulsating white dwarf R548 based on fits to newly detected periods and the use of the forward method. Based on an unexploited CFHT/LAPOUNE broadband photometric campaign of high S/N, we are able to obtain a finer frequency spectrum and uncover two triplets, two doublets, and two singlets. The low-amplitude pulsator R548, located in the hotter region of the ZZ Ceti instability strip, shows a stable and quite uncomplicated light curve. For that matter R548 is an ideal candidate for carrying on a complete asteroseismological analysis within the framework of the adiabatic approximation to obtain optimized atmospherical parameters. A more precise picture of the internal structure and composition of R548 will then be unraveled.
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Extreme amplitude variations of the pulsating DB white dwarf PG 1456+103 observed
with the Whole Earth Telescope Gerald Handler Nicolaus Copernicus Astronomical Center, Poland gerald@camk.edu.pl
PG 1456+103 was chosen as a WET target because it exhibited a complicated pulsation pattern not resolvable from a two-site photometric campaign (Handler, Metcalfe & Wood 2002). Pre-WET observations however showed that the pulsations had almost completely disappeared. They grew in amplitude during the WET run to reach their "normal" values one month after the global network observations. We document the amplitude changes and attempt to interpret them along with asteroseismic inferences.
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Discovery of pulsations in He-core, extremely low mass WDs JJ Hermes University of Texas at Austin, United States jjhermes@astro.as.utexas.edu
After an extensive search, we detail the discovery of the first extremely low mass (< 0.2 Msun), putatively He-core pulsating WD, SDSSJ1840+6423. This DA is by far the coolest and the lowest-mass pulsating WD, with an effective temperature of 9100 ± 170 K and log g = 6.22 ± 0.06, which corresponds to a mass of ~0.17 M_sun. This low-mass pulsating WD greatly extends the DAV (or ZZ Ceti) instability strip, effectively bridging the log g gap between WDs and main-sequence stars. We detect high-amplitude variability on timescales exceeding 4000 s, with a non-sinusoidal pulse shape. Our observations also suggest that the variability is multi-periodic. The star is in a 4.6 hr binary with another compact object, most likely another WD.
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Whole Earth Telescope Observations of BPM31594 and EC04207-4748 Judith Provencal University of Delaware and Mt. Cuba Observatory, United States jlp@udel.edu
We present preliminary results of Whole Earth Telescope (WET) observations of BPM31594 and EC04207-4748. Both targets were observed during XCOV28, from October to December 2011. These stars are bright, large amplitude pulsators. Both are potential targets for convective light curve fitting.
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The Puoko-nui CCD Time-series Photometer P. R. Chote and D. J. Sullivan Victoria University of Wellington, New Zealand denis.sullivan@vuw.ac.nz
We have developed a flexible CCD photometer that is built around a Princeton Instruments 1k x 1k frame transfer CCD that we operate without a shutter. The frame transfers and hence the exposure times are initiated by an external GPS conditioned signal that is produced by a custom microprocessor unit. This microprocessor receives signals from a GPS receiver and communicates time stamps to the data acquisition computer via a USB serial connection. While observing we run custom software "simultaneously" in separate threads on the acquistion computer that extract photometry from the CCD frames, calculate the evolving DFTs and display appropriate results on a monitor. When mounted on the 1m telescope at Mt John University Observatory in NZ we are able to autoguide the instrument using a small SBIG CCD attached to an offset guiding box. Our photometer is ideal for monitoring the pulsating white dwarfs stars.
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Whole Earth Telescope observations of the ZZ Ceti pulsator HS 0507+0434B Gerard Vauclair Institut de Recherche en Astrophysique et Planetologie (IRAP), France (Metropolitan) gvauclair@irap.omp.eu
HS 0507+0434B has been the main target of the WET campaign in November-December 2011. I will present the preliminary results of the data reduction and analysis.
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The PG1159 star SDSS J0349-0059 is a GW Virginis star Brian Warner, Patrick Woudt University of Cape Town, South Africa Brian.Warner@uct.ac.za
Among the hot hydrogen-deficient subdwarfs known as PG1159 stars there are 19 that show non-radial pulsations and are known as GW Vir stars Quirion (Comm. in Asteroseismology 159, 99, 2009). We find from high speed photometry in 2007 and 2009 of the PG1159 star SDSS J0349-0059 that it is a GW Vir star with principal periods at 418.9, 416.4, 349.0 and 517.8 s.
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Luminosity Function, mass distribution and populations
White dwarf population statistical analysis Monika Rybicka, Krzysztof Krzeszowski, Agnieszka Słowikowska University of Zielona Góra, Poland rybicka.monia@gmail.com
Villanova University White Dwarf Catalog contains almost 13 000 white dwarfs (WDs). Different WD types show different properties (e.g. Brightness, magnetic field). We present population wide statistical analysis of various WD properties. Analysis includes, but is not limited to e.g. distribution analysis and correlations. The analysis is performed using Python and R programming languages.
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Monte Carlo simulations of the hot white dwarf luminosity function Santiago Torres Universitat Politecnica de Catalunya, Spain santi@fa.upc.edu
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, for both DA and non-DA white dwarfs. We find an excellent agreement with the observational data for non-DA white dwarfs and a paucity of white dwarfs of the DA type at very high effective temperatures.
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White Dwarf structure and evolution
Assessing the impact of axion emission in the cooling of white dwarf Marcelo Miguel Miller Bertolami Univ. Nacional de La Plata, Argentina mmiller@fcaglp.unlp.edu.ar
Recently, it has been shown that the shape of the luminosity function of white dwarfs can be a very powerful tool to check for the possible existence of axions, a proposed but not yet detected weakly interacting particle. In order to make a correct assessment of the impact of the axion emission in the cooling of white dwarfs, detailed models that take into account the feedback of the axion emission into the thermal structure of the white dwarf are needed. In this work we present computations of white dwarf cooling sequences that take into account the effect of axion emission in a self consistent way by means of full stellar evolution computations. Then, we analyze the impact of the axion emission in the white dwarf luminosity function and derive constraints on the possible axion masses.
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Towards a standardised line list for G191-B2B, and other DA type objects. Simon Preval, M. A. Barstow, J. Holberg, N. J. Dickinson University of Leicester, United Kingdom sp267@le.ac.uk
We present a comprehensive analysis of the far UV spectrum of G191-B2B over the range of 900-1700A using co-added data from the FUSE and STIS archives. While previous identifications made by Holberg et al 2003 are re-affirmed in this work, it is found that some absorption features may have been overlooked. Future work includes extending this detailed analysis to a wider range of DA objects, in the expectation that a more complete analysis of their atmospheres can be realised.
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UV Spectroscopy of DO-Type White Dwarfs: PG 1034+001 and PG 0038+199 M. Mahsereci, T. Rauch, K. Werner, & J. W. Kruk Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Germany rauch@astro.uni-tuebingen.de
We present results of a NLTE spectral analysis of the two DO-type white dwarf stars PG 1034+001 and PG 0038+199.
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(F)UV Spectroscopy of Hot, Hydrogen-Rich Post-AGB Stars M. Ziegler, T. Rauch, K. Werner, & J. W. Kruk Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Germany rauch@astro.uni-tuebingen.de
We present spectral analyses of 15 DAO- and O(H)-type central star that represent well the stellar extremely hot, hydrogen-rich post-AGB evolution. We analyze high-resolution and high-S/N UV spectra obtained with FUSE and HST/STIS with models that comprise state-of-the-art fully metal-line blanketed NLTE stellar model atmospheres as well as models of the interstellar line absorption.
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Determination of the core composition of white dwarfs in M67 Amélie Simon, G. Fontaine, P. Brassard Université de Montréal, Canada amelie@astro.umontreal.ca
As the rates of helium thermonuclear burning are uncertain, the exact proportions of carbon and oxygen in the cores of white dwarfs are still unknown. But the cooling time depend on such a proportion. Hence, the luminosity functions for populations of white dwarfs with various compositions will not be the same. By comparing theoretical luminosity functions computed for populations of white dwarfs with different ratios of carbon and oxygen, with the observed luminosity function of M67, star cluster for which we have a precise knowledge of its age, we are able to infer the mean proportion of carbon and oxygen in the white dwarfs of M67. I will present the computation of 100 state-of-the-art evolutionary sequences that include convection, stellar wind, accretion and the latest results on the equations of state, radiative and conductive opacities.
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Observations and Modelling of DQ White Dwarfs Tommi Vornanen University of Turku, Finland ttvorn@utu.fi
We present observations and modelling of 12 DQ white dwarfs. Spectropolarimetric observations were made with FORS/VLT and ALFOSC/NOT. Modelling is based on the method presented in Berdyugina et al (2005). We use the model to fit the C_2 absorption bands to get atmospheric parameters in different configurations, including stellar spots and stratified atmospheres, searching for the best possible fit.
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White Dwarf catalogs and surveys
Studies of white dwarfs with a Low-cost EUV observatory Martin Barstow University of Leicester, United Kingdom mab@le.ac.uk
The various demands on funding agencies make it difficult to sustain the level of expenditure required to provide the broad range of space astronomy missions that the research community would like to have available. Multi-billion pound/dollar observatories such Chandra, XMM-Newton and HST have been enormously successful, but JWST has been delayed and plans for an equivalent large X-ray mission seem to be on-hold. Furthermore, the medium size ESA and NASA missions provide only a small number of opportunities over the next decade. Much exciting and important science, by default, will not be done. If satellite mission costs could be reduced significantly, by a factor of 5-10, we would open up a new parameter space of opportunity that is not currently offered by any agency. Significant improvement in instrument technology coupled with simplification of optical systems and the development of efficient, high performance small satellite platforms and ground systems has led to the prospect of the development of some low-cost opportunities. In this paper, we outline one such possible mission, based on a successful sounding rocket-borne payload. This comprises a high throughput normal incidence extreme ultraviolet spectrometer, with the design adapted for accommodation on the SSTL 300 platform. We make use of a segmented diffraction grating to provide an overall wavelength coverage from ~170-250Å by tuning the multi-layers of the individual elements to different, overlapping ranges. We outline the capability and science goals of the mission, and how they influence the design and operation of the satellite platform. We conclude with a discussion of how missions of this type operating both as constellations and as formation flying sparse apertures, could offer a scientifically viable alternative to monolothic 'great observatory' missions in the future.
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A catalogue of integrated Halpha fluxes for ~1100 Galactic planetary nebulae Ivan Bojicic Macquarie University, Australia ivan.bojicic@mq.edu.au
We present new determinations of the integrated Halpha flux for ~1100 Galactic planetary nebulae measured from the Southern H-Alpha Sky Survey Atlas (SHASSA) and its northern counterpart, the Virginia Tech Spectral-Line Survey (VTSS). This catalogue is the largest homogeneous database of its kind, tripling the number of currently available measurements.
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White Dwarfs with Gaia Silvia Catalan University of Hertfordshire, United Kingdom s.catalan@herts.ac.uk
The Gaia mission (ESA) will begin observing very soon (launch is scheduled in 2013) and the scientific community is preparing for the maximal scientific return. Gaia will determine positions, parallaxes and proper motions for a relevant fraction of the stars in our Galaxy (∼ 1% of the Galaxy). This census will be complete for all sources in the sky with G < 20, improving considerably the number of faint white dwarfs (WDs) and members of the halo population. Gaia will be very helpful to detect WD close to the cut-off in luminosity and even fainter. Using synthetic stellar spectral energy distribution libraries and the most recent Gaia transmission curves, we derive Gaia colours of three different kinds of WD (pure-H, pure-He and Mixed composition with H/He= 0.1). Relationships and colour-colour diagrams between different common photometric systems (Johnson-Cousins, SDSS and 2MASS) and Gaia are provided allowing making predictions of how WDs will look like in Gaia BP/RP spectrophotometry. We also compare the estimations of number and types of WD that will be observed considering different simulators: the Gaia Universe Model Simulator (GUMS), used in the preparation of Gaia mission, and one developed specifically for the study of WD populations (Napiwotzky, 2009). Our estimations provide that some thousands of cool WDs (Teff<5000K) will be detected for the first time with Gaia.
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A preliminary spectroscopic analysis of Hyades white dwarfs Alexandros Gianninas University of Oklahoma, United States alexg@nhn.ou.edu
Schilbach & Roser (2012) present kinematic and photometric data for 37 white dwarfs including the 10 classical Hyades white dwarfs (von Hippel, 1998) but also for a number of white dwarfs that fulfil the same kinematic and photometric criteria and are co-moving with the cluster. If these are indeed former cluster members, the number of confirmed Hyades white dwarfs could effectively be doubled. It so happens that many of the white dwarfs in Schilbach & Roser (2012), be they confirmed Hyades members or not, are included in the sample of Gianninas et al. (2011). Consequently, we are in a position to perform a spectroscopic analysis of the cluster members using the most recent generation of model atmospheres coupled with high signal-to-noise ratio observations of each star. Of particular interest is a new determination of the mean mass of the Hyades white dwarfs which has previously been shown to be higher than the mean mass of field white dwarfs.
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Prospects for cool WD science from PanSTARRS Nigel Hambly Institute for Astronomy, Edinburgh University, United Kingdom nch@roe.ac.uk
We discuss the prospects for new deep, wide-angle surveys of the Galactic white dwarf populations using data from Pan-STARRS: the Panoramic Survey Telescope & Rapid Response System.
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Determining radial velocities of white dwarfs with Gaia without spectra?
Stefan Jordan, Jos de Bruijne Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Germany
jordan@ari.uni-heidelberg.de
The poster discusses the possibility and limitations to measure radial velocities astrometrically by means of the perspective acceleration with the Gaia satellite. Spectroscopically Gaia can only measure radial velocities with the Radial Velocity Spectrometer in the wavelength range from 8470-8740 \AA where white dwarfs usually do not show any spectral features. Therefore, it would be desirable to measure radial velocity astrometrically by the change of the parallax during the 5 year mission of the satellite. If additionally radial velocities from the H$_alpha$ NLTE cores would be available such an astrometric determination would allow to disentangle the gravitational red shift. In this poster a crude approximation is performed in order to see whether this is possible.
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A Spectroscopic Census of White Dwarfs Within 40 parsecs of the Sun Marie-Michèle Limoges Université de Montréal, Canada limoges@astro.umontreal.ca
We describe here the basis of the method that will lead to a catalog of white dwarfs within 40 parsecs of the Sun, which will significantly increase the completeness of the current census. White dwarf candidates are identified from the SUPERBLINK proper motion database, allowing us to investigate stars down to a proper motion limit as low as 40 mas yr-1. This sample minimizes the kinematic bias and has the potential to provide a statistically complete census of white dwarfs to a significantly larger distance. The selection criteria and distance estimates are based on a combination of color-magnitude and reduced proper motion diagrams. Spectroscopic observation campaigns reveals 195 newly identified white dwarfs. The atmospheric parameters for a sample of 86 spectroscopically confirmed white dwarfs is presented. Our sample is rich in objects of particular astrophysical interest, such as white dwarfs with M dwarf companions, and unresolved double degenerate binary candidates. Finally, we present white dwarfs identified as candidates within the 20 pc sample.
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Synthetic light curves of born again events: First Results Marcelo Miguel Miller Bertolami Univ. Nacional de La Plata, Argentina mmiller@fcaglp.unlp.edu.ar
The development of surveys which will be able to cover a large region of the sky several times per year will allow the massive detection of transient events taking place in timescales of years. In particular, this projects will allow the detection of stars undergoing slow eruptions as those expected in the post-AGB evolution (LTP, VLTP scenarios). In order to identify those transients which correspond with late helium flashes the development of synthetic lightcurves of those events is mandatory. In this connection we present first results of a project aimed at computing grids of theoretical light curves of born again stars and other slow eruptive events.
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Theoretical White Dwarf Spectra via the Internet: Quality Control Ellen Ringat Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Germany ringat@astro.uni-tuebingen.de
The first decade of the Virtual Observatory (VO) build up services and tools for data conservation, handling, processing, analysis, etc. A new challenge in the immensely growing VO in operation is continuous quality control at different authority levels. Here we shed light on various aspects of theoretical white dwarf spectra that are provided via the registered TheoSSA VO service. We present benchmark tests that enable the VO user to judge their quality.
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Spectroscopic and photometric studies of white dwarfs in the Hyades Tremblay, P.-E., Schilbach, E., Roeser, S., Jordan, S., Goldman, B., Ludwig, H.-G. Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Germany ptremblay@lsw.uni-heidelberg.de
The Hyades cluster is known to harbour ten so-called classical white dwarf members. Numerous studies through the years have predicted that more than twice this amount of white dwarfs should be associated with the cluster. Reasons for this discrepancy could be that white dwarfs are ejected from the cluster due to kicks in the late phases of stellar evolution or that wrong assumptions have been made on the high-mass tail of the IMF. On the other hand, it is also possible that white dwarf members outside of the tidal radius have not yet been identified. Using the PPMXL catalog of proper motions and positions, members of our group have proposed 17 new Hyades white dwarf candidates. We will review the Hyades membership of these candidates by using spectroscopic and photometric observations, as well as simulating the contamination from field white dwarfs.
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Central stars of planetary nebulae
Central stars of Milky Way bulge planetary nebulae Krzysztof Gesicki Centrum Astronomii UMK, Poland Krzysztof.Gesicki@astri.umk.pl
The kinematical method for deriving the masses of central stars of planetary nebulae has been re-callibrated with the Milky Way bulge high quality data. The new data allow for discussion of the star formation history of the bulge.
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A Heavy-Weight post_AGB Star: The Exciting Star of the Planetary Nebula NGC 246 Thomas Rauch, E. Ringat, K. Werner, & J. W. Kruk Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Germany rauch@astro.uni-tuebingen.de
We present the NLTE spectral analysis of one of the most massive PG 1159-type stars, the central star of the planetary nebula NGC 246.
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SN Progenitors
Supernova type Ia progenitors as supersoft X-ray sources Mikkel Nielsen Dept. of Astrophysics, Radboud University Nijmegen, Netherlands M.Nielsen@astro.ru.nl
Supernova type Ia progenitors as supersoft X-ray sources. The nature of type Ia supernova progenitors remains unclear, despite more than 30 years of research. Two progenitor scenarios are normally considered: that of a massive white dwarf accreting material from a non-degenerate companion (the single-degenerate scenario), and that of a merging double white dwarf binary (the double-degenerate scenario). The X-ray signatures of the two scenarios are expected to be quite different, and we expect to detect 'naked', nearby, single-degenerate progenitors as supersoft X-ray sources (van den Heuvel et al. 1992). However, so far, searches of the Chandra archive has yielded 10 non-detections and one possible, but somewhat ambiguous, detection (Nielsen et al. 2012). We discuss this search and the implications for determining the nature of type Ia supernova progenitors, as well as the possible importance of obscuration by local material lost from the progenitor systems into the circumbinary region (Nielsen et al. in prep.).
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White Dwarfs in Detached Binaries
White dwarf - Brown dwarf binaries: The use of white dwarfs in the calibration
of ultracool atmospheres. Avril Day-Jones Universidad de Chile, Chile adjones@das.uchile.cl
We present our program to identify white dwarf- brown dwarf binary systems from sky surveys such as SuperCOSMOS, SDSS, 2MASS and UKIDSS. Systems containing a white dwarf and a brown dwarf are rare but can be used to place constraints on the age of the binary, making them valuable benchmark systems. It is currently not possible to calculate brown dwarf ages from models alone and white dwarfs provide an opportunity to aid the calibration of these models. We present preliminary findings of our benchmark binary search and review the level of constraints currently provided by benchmark objects. Finally we describe the niche age space that white dwarf - brown dwarf binary systems can provide and look at how more systems may be identified in future surveys, such as VISTA and WISE.
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Detection of the orbital motion of RE J0317-853 & LB 9802 Katherine Lawrie University of Leicester, United Kingdom kal27@le.ac.uk
We have photometrically monitored RE J0317-853, a rapidly rotating (P=725s), highly magnetic (300MG<B<800MG), massive (M~1.3Msun) white dwarf, since 1994 to determine whether any changes have occurred in the arrival time of the maximum flux. The O-C analysis reveals we have detected changes in the arrival time of maximum flux for RE J0317-853, consistent with that expected from the orbital motion of the wide binary pair of RE J0317-853 and LB 9802, proving they are in a bound system. An orbital period of ~2095 years is obtained, agreeing with estimates by Kulebi et al. (2010), although we are as yet unable to constrain the eccentricity of the system. In addition, a parabolic fit to the residuals gives an upper limit on the spin-down timescale of 10^9 years, which is comparable to the spin-down expected by magnetic-dipole radiation assuming a minimum B-field of 800 MG.
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A versatile and accurate tidal capture code for the use with the stellar population
synthesis models. Niyas Madappattu Alikutty Macquarie University, Australia niyas.alikutty@mq.edu.au
The tide raised by a companion on a giant primary star can play a very important role both on the primary and on the orbital elements. Depending on the strength of the tide, the companion can be captured into a common envelope and go on to form a close binary or a merger. The tides raised by companions heavier than approximately 0.1 solar masses can also transfer enough angular momentum from the orbit to the giant's spin, thus significantly affecting the primary's rotation rate. We have developed a code that implements tides using the formalism of Zahn (1989) with a variable tidal strength and using accurate stellar evolutionary tracks calculated with the Modules for Experiments in Stellar Astrophysics (MESA) code. By using fitting formulae we have derived prescriptions to determine capture radii, timescales, and primary rotation rates as a function of companion and primary masses, as well as different mass-loss mechanisms and tidal strength parameters. These can be implemented into stellar population synthesis models. The effects of uncertainties on the stellar evolutionary calculations, for example during the thermally pulsating asymptotic giant branch phase are evaluated.
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Investigations of a new eclipsing cataclysmic variable HBHA 4705-03 D.G. Yakin, V.F. Suleimanov, V.V. Shimansky, V.V. Vlasyuk, O.I. Spiridonova Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Germany suleimanov@astro.uni-tuebingen.de
We present results of photometric and spectroscopic investigations of the eclipsing disc cataclysmic variable star HBHA\,4705-03. Emission spectra of the system are similar to the spectra of UX UMa and show broad one-peaked hydrogen and ionized helium emission lines which are become double-peaked near the eclipse. Doppler maps for the hydrogen lines demonstrate that a significant part of the emission arises near the inner Lagrange point due to an irradiation of the vertically extended bright spot and the secondary by the inner disc hard radiation. Masses of the components ($M_{\rm WD} = 0.54 \pm 0.10 M_{\odot}$ and $M_{\rm RD} = 0.45 \pm 0.05~ M_{\odot}$), and the orbit inclination ($i = 71.^{\circ}8 \pm 0.^{\circ}7$) were estimated using the information about the eclipse duration and the radial velocity amplitude obtained using HeI lines. We simulate light curves of the system and estimate the mass accretion rate ($\dot M = 2\times 10^{17}$\,g\,s^{-1}$) and the bright spot geometry.
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Physical Processes in White Dwarfs and Magnetic White Dwarfs
Very fast photometric and X-ray observations of the intermediate polar V2069 Cygni
(RX J2123.7+4217) Ilham Nasiroglu, Agnieszka Słowikowska, Gottfried Kanbach, Frank Haberl, Monika Rybicka University of Zielona Góra, Poland rybicka.monia@gmail.com
We present fast timing photometric observations of the intermediate polar V2069 Cygni (RX J2123.7+4217) using the Optical Timing Analyzer (OPTIMA) at the 1.3-m telescope of Skinakas Observatory. The optical (450-950 nm) light curve of V2069 Cygni was measured with sub-second resolution for the firsttime during 2009 July and revealed a double-peaked pulsation with a period of 743.38 +/- 0.25 s. A similar double-peaked modulation was found in the simultaneous Swift satellite observations. We suggest that this period represents the spin of the white dwarf accretor. Moreover, we present results from a detailed analysis of the XMM-Newton observation, which also shows a double-peaked modulation, however shifted in phase, with a period of 742.35 +/- 0.23 s. The X-ray spectra obtained from the XMM-Newton European Photon Imaging Camera (EPIC) instruments were modelled by a plasma emission and a soft blackbody component with a partial covering photoelectric absorption model with a covering fraction of 0.65. An additional Gaussian emission line at 6.385 keV with an equivalent width of 243 eV is required to account for fluorescent emission from neutral iron. The iron fluorescence (~6.4 keV) and Fe XXVI lines (~6.95 keV) are clearly resolved in the EPIC spectra. In the Porb -- Pspin diagram of intermediate polars, V2069 Cyg shows a low spin-to-orbit ratio of ~0.0276 in comparison with ~0.1 for other intermediate polars.
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Disk, Dust and Planets Around White Dwarfs
Frequency of Debris Disks at White Dwarfs Sara Barber The University of Oklahoma, United States sara.d.barber@me.com
The prevailing view of exoplanetary systems in post main-sequence is that asteroid analogues persist at a significant fraction of white dwarf remnants. These asteroids are likely to be scattered due to interactions with giant planets within the system and become tidally disrupted when passing close to the compact stellar remnant. The resulting debris disk can produce a detectable infrared excess. We present a sample of 119 cool hydrogen atmosphere white dwarfs from the Palomar-Green catalogue and find 5 with excess radiation in the infrared, translating to a $4.2^{+2.7}_{-1.2}\%$ frequency of debris disks. We extrapolate this result to main-sequence stars using the initial-final mass relation and conclude that a given main-sequence star of mass 1 − 7M⊙ has at least a 4.2% chance of hosting planets. Conversely, this result can be interpreted as a limit on disk lifetimes as a fraction of white dwarf cooling timescales. From this, we find that the average total accretion mass for our sample is about 0.003 − 3.4 times the mass of Pluto or 0.0006 − 0.6 times the mass of the Moon, indicating that white dwarfs may accrete moons and planets as well as Solar System asteroid analogues.
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Distribution of patterns and flow dynamics in accreting white dwarfs Daniela Boneva Space Research and Technology Institute, Bulgaria danvasan@space.bas.bg
In the diversity of white dwarf stars population it is clear that the behavior of the disc flow is not common and uniform for all the close binary stars. It is quite affected both by the influences of mass transfer parameters: velocity and density, and by the gravitational tidal effects. We aim to examine and compare the morphology of whole disc’s flows, implying the data of DN and DA types of white dwarfs in the calculations. It is employed with two different numerical codes and box-framed schemes in the models are proposed. The results demonstrate of how the dense patterns and waves evolve in the studying types of white dwarfs. An effect of their development to the whole disc’s shape and inner structure configuration is shown. We find a close relation between cooling - heating processes in the binary system and the patterns distribution there.
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Non-LTE Analysis of Gaseous Planetary Debris Disks around Single White Dwarfs Stephan Hartmann Kepler Center for Astro and Particle Physics, Germany hartmann@astro.uni-tuebingen.de
For several years now there is an evermore growing number of single white dwarfs detected showing a high flux excess in the infrared part of their spectra. Among other discussed explanations the idea of an evolved central object shredding parts of its surrounding planetary system was brought forward and high metallicity and mass of the hereby formed dusty debris disks fits the observed data very well. Most of the time spectral analysis of these objects focuses on the accreted material within the white dwarf's atmosphere, where it produces notable spectral signatures. Since some of those polluted white dwarfs do not only seem to host a dusty but also a gaseous disk we on the other hand decided to performed calculations to synthesize the spectral features of the disks gas content itself. This method provides the only possibility so far, to study the disk's material directly, before it is accreted onto the white dwarf.
We will present our latest detailed non-LTE modeling results obtained with our Tübingen Accretion Disk code AcDc. For some of the observed systems we looked at the spectral impact of the disk's surface density, effective temperature, or chemical mixture. Also investigations on the radial extensions and disk geometries were performed using the gas disk hallmark, the Ca II IR triplet.
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Thermohaline instabilities induced by heavy element accretion onto white dwarfs:
consequences on the derived accretion rates. Morgan Déal, Sylvie Vauclair, Gérard Vauclair Institut de Recherche en Astrophysique et Planétologie (IRAP), Toulouse, France gvauclair@irap.omp.eu
Heavy elements are observed in the atmospheres of many DA and DB white dwarfs, and their presence is attributed to the accretion of matter coming from debris discs. Several authors have deduced accretion rates from the observed abundances, taking into account the mixing induced by the convective zones and the gravitational settling. The obtained values are different for DA and DB white dwarfs. Here we show that an important process was forgotten in all these computations: thermohaline mixing, induced by the inverse mu-gradient built during the accretion process. Taking this mixing into account leads to an increase of the derived accretion rates, specially for DA white dwarfs, and modifies the conclusions.
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Investigating AM Her Cataclysmic Variables with the Optical Pulsar Timing Analyzer (OPTIMA). Agnieszka Słowikowska, Krzysztof Goździewski, Ilham Nasiroglu, Gottfried
Kanbach, Arne Rau, Krzysztof Krzeszowski
University of Zielona Góra, Poland aga@astro.ia.uz.zgora.pl
In this work, we focus on short--period eclipsing binaries that belong to the group of Cataclysmic Variables (CVs). They are known as Polars and Intermediate Polars, closely resembling their prototype AM Her. These binary stars consists of a red dwarf and highly magnetic white dwarf, whose orbital periods are a few hours only. Monitoring eclipses of these typically faint sources demand high resolution, precision photometry. We describe the very recent results obtained for two example CVs, HU Aqr and DQ Her with the help of a particular instrument OPTIMA.
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