| Tuesday 22 August 2006 (morning sessions 1/2) |
|
Welcome and Introductory address
|
| 09:00-09:30 | P. Harmanec (Czech Rep.) and E. Guinan (USA)
An Overview of Binary and Multiple Stars as Critical Tools & Tests in Contemporary Astrophysics – The Dawn of the Century of Discovery
The new and exciting developments in the studies of binary and multiple stars are discussed. An overview is given of the major topics and themes of IAU Symposium 240. These include new observing techniques and reduction methods for the study of binary and multiple star systems as well as the important astrophysical quantities that can be uncovered from such observations. Emphasis is given to new developments that include results from high resolution interferometry and high precision photometry and spectroscopy as well as results from multi-wavelength and panoramic photometry programs of binaries both inside and outside the Galaxy. Also discussed are the uses of binary and multiple star systems as critical tools for the study and tests of many important aspects of modern astrophysics. To give a few examples, binary and multiple stars are playing major roles in (1) testing stellar evolution theory (by providing fundamental stellar quantities), (2) cosmology (standard candles for improving the cosmic distance scale), (3) probes of galactic structure (e.g. from fragile binaries), as well as (4) providing tests of stellar structure and General Relativity (apsidal motion studies). Also binary systems with accreting degenerate components (like CVs and XBs) provide miniature laboratories of the study of accretion processes found in AGN galaxies. These are but a few out a very large number of exciting topics discussed at the symposium. Also discussed are the new classes of binary stars that include binary systems with planetary and brown dwarf components. The future of the study of binary stars also will be briefly addressed and discussions of new opportunities and the challenges with upcoming new instrumentation, telescopes and space missions will be be noted. For example, one major (but very exciting) problem will be how get the most scientific rewards from the huge number (millions) of additional binaries expected to be discovered from wide field synoptic surveys both from the ground and from space.
This work was, in part, sponsored by Grants from the US National Science Foundation and NASA which we gratefully acknowledge. Also I would like to acknowledge travel support from a grant from the NSF to the AAS.
|
|
I. New Observing Techniques and Reduction Methods
|
|
Observing with high angular and spectral resolution
|
| 09:30-10:10 | H. McAlister (USA)
Overview of Multiple-Aperture Interferometry Binary Star Results from the Northern Hemisphere
Long-baseline optical interferometry can nearly close the gap in selection space between astrometric and spectroscopic detection of binary star systems, bringing the complementary powers of astrometry and spectroscopy to bear on a complete dynamical understanding of such systems, particularly including the determination of the masses of the individual stellar components. In the case of double-lined spectroscopic systems, their resolution by long-baseline interferometry also yields the orbital parallax and hence the luminosities of the individual stars. In some of these cases, the angular diameters of one or more components are accessible, and so a complete specification of a star in terms of its mass, radius and luminosity is made.
The northern hemisphere is now equipped with several interferometers of unprecedented capability in terms of their baseline sizes, numbers of telescopes and telescope apertures. These instruments, most notably the Navy Prototype Optical Interferometer near Flagstaff and the Palomar Testbed Interferometer at Mt. Palomar Observatory, have produced very significant results of a number of interesting systems fulfilling interferometry's promise to produce fundamental astrophysical data at levels of accuracy that challenge or confirm astrophysical theory. Now scientifically operational, the CHARA Array on Mt. Wilson can be expected to contribute productively to this field as well.
This paper will summarize the binary star results from northern interferometers and give specific examples of their broad impact on binary star astronomy.
|
| 10:10-10:30 | J. Davis (Australia)
Overview of Multiple-Aperture Interferometry Binary Star Results from the Southern Hemisphere
The first multiple-aperture interferometric study of a binary system, in which the power of combining interferometric and spectroscopic data was demonstrated, was made from the Southern Hemisphere. The observations of Alpha Virginis with the Narrabri Stellar Intensity Interferometer (NSII), made in 1966 and 1970, were combined with spectroscopic and photometric data to yield the mass, radius and luminosity of the primary component as well as an accurate distance to the system. The NSII also revealed a number of stars, previously thought to be single, to be binary systems but the instrument lacked the capability to determine their orbits. Several of these systems have subsequently been shown to be spectroscopic binaries and, more recently, the Sydney University Stellar Interferometer (SUSI) has been used to determine interferometric orbits for some of them. In combination with spectroscopic data the SUSI results have led to accurate values for the masses of early type stars and accurate distances to the systems. Gamma 2 Velorum, the brightest Wolf-Rayet binary system, has recently been observed with SUSI to determine its orbit and, in combination with spectroscopic data, to determine the masses for the O-type giant and Wolf-Rayet (WC8) component stars and the distance to the system. The status and future plans for the SUSI programme will be described.
The other Southern Hemisphere multiple-aperture optical/IR interferometric instrument is the European Southern Observatory’s Very Large Telescope Interferometer (VLTI). To data few observations of binary systems have been made with the VLTI but the status and plans for the future will be outlined.
|
| 10:30-10:50 | M. Shao (USA)
Space-based Long Baseline Interferometry for a New Era of Binary Star Research
Long baseline interferometry in space offers new observational capabilities that are unmatched by other facilities. This paper describes the capabilities of the SIM Planet Quest mission for the study of binary stars, across a broad range of stellar types. Approved key projects include studies of binaries where the companion could be as small as terrestrial planet to potentially supermassive black hole binaries and many common and uncommon objects inbetween. SIM has several observational capabilities to study binaries. The most obvious is astrometry. But in addition to 1 microarcsecond relative astrometry SIM has the capability to make astrometric measurements in an inertial frame to ˜4 uas.
While astrometric accuracy is the main reason for SIM, an interferometer In space should be capable of very accurate fringe amplitude measurements. For binaries where both objects are luminous and separated by more than a few 10’s milliarcsecond SIM can measure both component’s position and relative intensities at multiple wavelengths.
|
| 10:50-11:20 | Y. Balega (Russia)
Interferometry with single telescopes
visible and IR speckle interferometry, adaptive optics, HST FGS, other single-aperture techniques |
| 11:20-11:50 | A. Hatzes (Germany)
High Precision Stellar Radial Velocity Measurements
Over the past 50 years the typical stellar radial velocity measurement error has decreased from about 1000 m/s to the current best precision of about 1 m/s, or more than two orders of magnitude. This increase in precision has produced an explosion in the number of extrasolar planets that have been discovered. Modern day radial velocity measurements are now pushing the mass detection limits for sub-stellar companions from Jupiter- to Neptune or "super Earth" masses. I will review the various radial velocity measurement techniques in use today and their advantages and disadvantage. Recent results from the detection of extrasolar planets will also be presented. Although precise stellar radial velocity measurements have highlighted the field of extrasolar planets, these are still a valuable tool for the study binary stars. I will discuss the impact such high precision radial velocity measurements may have on future studies of binary stars. |
|
Poster highlights 15 min
|
| | F.C. Fekel
Spectroscopic Binary Candidates For Interferometers
We present a progress report on a program to improve the orbits of known spectroscopic binaries that are potential targets for ground-based optical interferometers, such as the CHARA array and PTI. The combination of such observations results in three-dimensional orbits that produce very accurate masses (uncertainties of 0.1-0.2% in the best cases) as well as orbital parallaxes that are generally more precise than those from Hipparcos. Additional analyses determine other basic parameters of the stars. The components can then be compared with theoretical evolutionary tracks. Extensive observing began in 2002 April, and we are currently obtaining high-resolution, red-wavelength spectra at McDonald Observatory, Kitt Peak National Observatory, and Fairborn Observatory. For 40 systems we have accumulated 10 or more spectra that show resolved components. Results to date are highlighted. |
| | A. Richichi
Interferometric investigations of eclipsing binaries as a key to an improved distance scale
Binary and multiple systems constitute one of the main tools to obtain fundamental stellar parameters, such as masses, radii, effective temperatures and distances. One especially fortunate, and at the same time rare, occurrence is that of double-lined eclipsing binaries with well-detached components. In this special case, it is possible to obtain a full solution of all orbital and stellar parameters, with the exception of the effective temperature of one star, which is normally estimated from spectral type, reddening-corrected photometric colors, or derived from atmospheric analysis of the spectrum. Long-baseline interferometry at facilities such as the ESO VLTI is beginning to have the capability to measure directly the angular separation and the angular diameter of some selected eclipsing binary systems, and we have proposed such observations with the AMBER instrument.
In particular, we aim at deriving directly the effective temperature of at least one of the components in each binary system by iterative convergence of the orbital solution and of the interferometric measurements, thereby avoiding any assumptions or required external calibration in the global solution through the Wilson-Devinney method. We will also obtain an independent check of the results of this latter method for what concerns the distance to the systems.This represents a first step towards a global calibration of eclipsing binaries as distance indicators. Our results will also contribute to the effective temperature scale for hot stars.The extension of this approach to a wider sample of eclipsing binaries could provide an independent method to assess the distanceto the LMC.
|
| Tuesday 22 August 2006 (afternoon sessions 3/4) |
|
New possibilities for standard observational techniques
|
| 12:00-12:30 | I. Ribas (Spain)
The Orbit and Properties of the BD+60 73 + IGRJ00370+612 Supergiant X-Ray Binary
Spectrograms of the blue and H alpha regions of BD+60 73 obtained with the Cassegrain spectrograph on the David Dunlap Observatory 1.88 m telescope have been measured for radial velocities. These measures confirm that BD+60 73 is a single-line spectroscopic binary with the same period, 15.665 d, as the x-ray flux variations of IGRJ00370+612. The x-ray maxima occur at or just after the time of periastron passage, even though the eccentricity e=0.37 does not seem large enough to produce a large increase in the mass flux at the position of the compact object at the time of periastron passage. The mass function combined with a plausible range of possible masses for a neutron star companion yields primary masses within the range expected for the spectral type of BD+60 73. The compact companion cannot be a black hole unless the supergiant has an exceptionally high mass for its B1Ib spectral type or the inclination of the orbit is very low. The H alpha line shows weak, variable emission, but we have insufficient data to test whether these variations are correlated with orbital phase. We note, as have other authors, that BD+60_73 is projected on the sky within the bounds of Cas OB5. It also lies close to the “adolescent” supernova remnant CTB1. However, the binary system has a radial velocity of approximately -40 km/s with respect to Cas OB5.
|
| 12:30-13:00 | A. Bonanos (USA)
Over 7000 eclipsing binaries have been discovered in the Local Group through various variability surveys in the last decade. Measuring fundamental parameters of these eclipsing binaries has become feasible with 8 meter class telescopes, making it possible to use eclipsing binaries as distance indicators. Distances with eclipsing binaries provide an independent method for calibrating the extragalactic distance scale and thus determining the Hubble constant. I will review the distance determinations to eclipsing binaries in the LMC, SMC and M31 and present the DIRECT Project distance determination to a detached binary in M33.
|
| 13:00-13:30 | B. Mason (USA)
The database of visual double star data has experienced tremendous changes, doubling in size during the last 25 years and growing at an ever increasing rate. Interferometric techniques have allowed the database to extend to much closer separation (and shorter periods), while longer timebases and higher-precision wide-field surveys have increased our knowledge of common proper motion pairs at the widest separations.
These changes in the database are highlighted, describing the evolution of methods of observation (both historically and the past few years) and the effectiveness of these various methods in different regimes of separation/period space. The various niches for wide- and narrow-field work as applied to double and multiple stars are examined and the different types of information which each can provide are also highlighted.
After more than 20 years of successful work, speckle interferometry and conventional CCD astrometry have replaced filar micrometry and photography as the preferred classical techniques. Indeed, most work in filar micrometry is now being done by amateurs, although much of that community is also switching to CCDs and other electronic techniques.
Despite the significant growth of the double star database, much still remains to be done, such as finding lost pairs, filling in missing parameters so that observing programs may be more efficient at observing stars appropriate to their capabilities, and providing at least approxmate kinematic descriptions.
Work on pairs described as neglected at the time of the last major WDS data release (2001) is given as a specific example of recent improvements, and finally the continued need to publish data using classical double star parameters is discussed.
|
| 13:30-13:45 | W. Hartkopf (USA)
Due to improvements in technology (interferometers, precision radial-velocity techniques, etc.), the traditional separation/period regimes of "wide" and "close" binaries are witnessing increasing overlap. This is expected to lead to increasing confusion in component identification when systems are studied using multiple techniques, since different observing techniques have adopted their own (often dissimilar) rules for designation of these components.
A quick overview will be given of the Washington Multiplicity Catalog, an effort to mitigate this confusion by creating a common nomenclature scheme for all types of stellar and sub-stellar companions.
|
|
Improved methods of data analysis
|
| 13:45-14:25 | H. Hensberge (Belgium) & K. Pavlovski (Croatia)
Modern Techniques for the Analysis of Spectroscopic Binaries
Spectroscopic binaries are fundamental sources of precise basic stellar parameters. Composite spectra of multiple systems are used to determine orbital parameters, and more recently to reconstruct component spectra. Techniques used to obtain these goals include measurement of positions of single spectral lines, cross-correlation using template spectra or hardware masks, two-dimensional cross-correlation, determination of broadening functions, subtraction of a template for the primary component, Doppler tomography, spectral separation and spectral disentangling. An overview of these techniques will be given pointing out relations between them, basic limitations, strengths and, when appropriate, implications for the observing strategy.
The second part of the talk will be devoted to a more detailed discussion of spectral separation and disentangling techniques using either the Fourier components of the composite spectra or their representation in velocity (logarithmic wavelength) space, with the aim to give the potential user insight in equivalence and practical differences between different approaches. An evaluation of the risks due to near-singularity of the involved equations and due to bias in the observations is made in the case of spectral separation of binary stars.
|
|
Poster highlights 40 min
|
| | N.R. Evans
Polaris: Mass and Multiplicity
Polaris, the nearest and brightest classical Cepheid, is a member of at least a triple system. It has a wide (18'') physical companion, the F-type dwarf Polaris B. Polaris itself is a single-lined spectroscopic binary with an orbital period of 30 years (Kamper, 1996, JRASC, 90, 140). By combining Hipparcos measurements of the instantaneous proper motion with long-term measurements and the Kamper radial-velocity orbit, Wielen et al. (2000, A&A;, 360, 399) have predicted the astrometric orbit of the close companion. Using the Hubble Space Telescope and the Advanced Camera for Surveys' High-Resolution Channel with an ultraviolet (F220W) filter, we have now directly detected the close companion. Based on the Wielen et al. orbit, the Hipparcos parallax, and our measurement of the separation (0.17 arcsec), we find a mass of 4.3 +/- 1.1 Msun for the Cepheid and 1.25 +/- 0.20 Msun for the close companion. These preliminary values will be refined as a result of additional HST observations scheduled for the next 3 years.
We have also obtained a Chandra ACIS-I image of the Polaris field.Two distant companions C and D do not have X-rays and hence are not young enough to be physical companions of the Cepheid. There is one additional stellar X-ray source in the field, located 253'' from Polaris A, which is a possible companion. Further investigation of such a distant companion is valuable to confirm the full extent of the system.
Support for this work was provided by grants HST-GO-10593.01-A and NAS8-03060, and also Chandra grant GO6-7011A and Chandra X-ray Center NASA Contract NAS8-39073 .
|
| | EJM Van den Besselaar
DE CVn: A Bright, Eclipsing Red Dwarf – White Dwarf Binary
DE CVn is a relatively unstudied eclipsing binary where one of the components is an M dwarf. Its brightness makes it an ideal system for a detailed study in the context of common-envelope evolution of a detached white dwarf – red dwarf binary with a relatively short orbital period (~8.7 hours). We present a detailed study of the basic parameters (e.g. orbital period, components' masses, spectral type) for this system from photometric and spectroscopic studies. The eclipses observed during several photometric observing runs were used to derive the ephemeris. We have used spectroscopic data to derive the radial velocity variations of the emission lines and these are used to determine the components' masses and the orbital separation. The secondary component in DE CVn is an M3 main-sequence star and the primary star, which is not visible in the spectra, is a cool white dwarf with a temperature of ~8000 K. From the photometry and spectroscopy together, we have set a limit on the binary inclination. This system is a post-common-envelope system where the progenitor of the present day white dwarf was a low-mass star (M<2 Msun). The time before DE CVn becomes a semi-detached system is longer than the Hubble time.
|
| | LPR Vaz
The Eclipsing Triple System U Ophiuchi Revisited
The absolute dimensions of the mid B-type eclipsing triple system U Oph were determined through a fully consistent analysis, taking into account both the exceptionally short period (˜21.2 yr) apsidal motion and both the third light and the light-time orbit around a tertiary star (period of ~38.4 yr). A new ephemeris was determined with the exact method proposed by Lacy and 353 - 229 primary, 124 secondary - times of minimum (selected out of 482 - 312 primary and 170 secondary - times from the literature, many referring to the same minimum). A modified version of the Wilson-Devinney (WD) code, adapted to treat systems with apsidal motion and/or light-time orbit effect with arbitrary atmosphere models for the stellar fluxes, was used to simultaneously analyze the 4 light (uvby–Hbeta system, obtained with the Strömgren Automatic Telescope at ESO, La Silla, Chile) and the radial velocity curves (Coudé spectrograph at the ESO 1.5 m telescope), with both the least-squares and the SIMPLEX minimization methods.
The derived absolute dimensions of U Oph and those of other 3 systems, whose components have similar masses, namely V760 Sco, MU Cas and DI Her, are used to control and compare the evolutionary models of the Padova Group and the ones by Claret, with the astrophysical quantities log g, log Teff, log M and the derived luminosities.
|
| | P. Hadrava
New Trends in Disentangling of the Spectra of Multiple Stars
The method of spectra disentangling has been applied in many studies on different stellar systems at various distances up to the Andromeda Galaxy. In some of these applications the underlying assumptions are not precisely satisfied. This is why new generalizations of the method are needed. Ways to overcome these problems will be discussed in the present contribution. |
| | R. Koehler
Binary Stars in the Orion Nebula Cluster
We report on a high-spatial-resolution survey for binary stars in the periphery of the Orion Nebula Cluster, at 5 – 15 arcmin (0.65 – 2 pc) from the cluster center.
We observed 228 stars with adaptive optics systems, in order to find companions at separations of 0.13 – 1.12 arcsec (60 – 500 AU), and detected 13 new binaries. Combined with the results of Petr (1998), we have a sample of 275 objects, about half of which have masses from the literature and high probabilities to be cluster members. We used an improved method to derive the completeness limits of the observations, which takes into account the elongated point spread function of stars at relatively large distances from the adaptive optics guide star. The multiplicity of stars with masses >2 Msun is found to be significantly larger than that of low-mass stars.
The companion star frequency of low-mass stars is comparable to that of main-sequence M-dwarfs, less than half that of solar-type main-sequence stars, and 3.5 to 5 times lower than in the Taurus-Auriga and Scorpius-Centaurus star-forming regions. We find the binary frequency of low-mass stars in the periphery of the cluster to be the same or only slightly higher than for stars in the cluster core (<3 arcmin from θ1C Ori). This is in contrast to the prediction of the theory that the low binary frequency in the cluster is caused by the disruption of binaries due to dynamical interactions. There are two ways out of this dilemma: Either the initial binary frequency in the Orion Nebula Cluster was lower than in Taurus-Auriga, or the Orion Nebula Cluster was originally much denser and dynamically more active.
|
| Wednesday 23 August 2006 (morning sessions 5/6) |
|
Improved methods of data analysis (continued)
|
| 15:00-15:15 | G. Peters (USA)
Bipolar Jets, Hot Interaction regions, and Colliding Winds in OB Interacting Binaries
Spectroscopic observations in the FUV during the past two decades have provided us with a wealth of information on plasma flows and interactions in OB interacting binary systems. In the 1980-90s data from the IUE spacecraft revealed a high temperature interaction region apparently associated with the gas stream impact and confirmed infall and outflow of gas stream material. In addition interaction regions associated with shocks due to colliding winds in close O-type binaries were discovered. More recently observations of Algol systems with OB mass gainers with the FUSE spacecraft have provided evidence of bipolar flows in several systems and revealed a well-defined accretion hot spot at the site of the gas stream impact in U Cep. In this talk the major plasma components associated with mass transfer that have been discovered by FUV spectroscopy are discussed with emphasis given to the newest observations. |
| 15:15-15:30 | G. Peters (USA)
Studying Magnetic Activity in Cataclysmic Binaries Using Near-IR Spectroscopy
Chromospheric activity on the secondary stars of cataclysmic variables (CVs) is a key ingredient for angular momentum loss from the system via magnetic braking. This effect is thought to drive the evolution of the system and is invoked to explain a number of observed properties of CV light curves, such as long-term modulations and high/low states. However, obtaining observational support for this magnetic activity has proven difficult. We present a new method of studying chromospheric activity on the secondary stars of CVs, using near-IR spectral features. We discuss in particular the magnetic CV (polar) AM Herculis, in which satellites to the H-alpha emission line are interpreted as arising from magnetically confined gas streams (prominences). This phenomenon provides a new technique for mapping magnetic structures on CV secondaries, and advances our understanding of the nature of magnetic structures and activity on CV secondaries.
|
| 15:30-16:00 | M. Richards (USA)
|
| 16:00-16:30 | K. Strassmeier (Germany)
Doppler imaging and eclipse maps of spotted stars
Many of the interesting spotted stars are in close binaries, where one can find almost any rotational period due to the rotational synchronization with the orbital motion. Binaries are thus good laboratories to study the impact of particular astrophysical parameters that nature usually does not make easily observable. On rapidly-rotating stars, we may indirectly resolve the surface by a tomographic imaging technique and map the surface temperature distribution as a proxy of the (predominantly radial) magnetic field. Binaries are not as straightforward to map as single stars and I will show some examples where it was successful and some where it failed. Eclipses help to further constrain the solution from line-profile variations and may give some clues on the amount of unresolved features in the images. I present one case of a bright giant of 100 solar luminosities in a close binary with even a deformed surface geometry but otherwise solar-type behavior. One of the basic goals is to learn about the impact of inter-binary magnetic fields on the evolution of binaries and stars in general and to provide conclusive constraints for numerical MHD models. |
| 16:30-17:00 | T. ten Brummelaar (Australia/USA)
comments on the first half of the symposium |
| 17:00-17:30 | R. Wilson (USA)
Models of Binary Star Observables over the Triennium
Innovation in synthesis and analysis of time-wise binary star observables (light curves, radial velocity curves, etc.) continued above its usual brisk pace over the triennium (mid-2003 to mid 2006), stimulated by planned space missions, by large surveys such as ASAS, Gaia, and the gravitational lens surveys, and by instrumental advances. Particularly notable are syntheses of observables beyond light and velocity curves such as line spectra and line profiles; surface and circum-stellar phenomena such as magnetic spots, extended atmospheres, and dynamic flows; binaries as distance indicators; and automated schemes to process enormous databases. Other work addressed advantages of working with light curves that are effectively or actually in absolute units; detection and analysis of multiple systems; accuracy of photometric mass ratios; effects of interstellar and Earth-atmosphere extinction on light curves, ephemerides from mixed whole light and velocity curves, user-friendly interface capability; and convergence and uniqueness of light curve solutions. Synthesized star and disk spectra are probing exotic systems such as cataclysmic variables, polars, and X-ray binaries. They also allow objective measurement of rotation via line profiles and meaningful analysis of systems with shallow or absent eclipses. Work on neural networks and on large archives promises to supply the starting parameter estimates needed by automated light curve solution programs that are intended mainly for surveys but may also be useful for individually observed objects. Distance estimation now can be self-contained and impersonal, with efficient through-put and standard errors, and can be applied fully as well to semi-detached and over-contact as to detached binaries. |
|
Poster highlights 30 min
|
| | D. Falceta-Gonçalves
Line-Profile Variations on Massive Binary Systems: determining eta Carinae orbital parameters
When the winds of two massive stars orbiting each other collide, an interaction zone is created consisting of two shock fronts at both sides of a contact surface. During the cooling process, elements may recombine generating spectral lines. These lines may be Doppler shifted, as the gas stream flows over the interaction zone. To calculate the stream velocity projected into the line of sight we use a simplified conical geometry for the shock fronts and, to determine the synthetic line profile, we have to sum the amount of emitting gas elements with the same Doppler shifted velocity. We show that the stellar mass loss rates and wind velocities, and the orbital inclination and eccentricity, are the main parameters on this physical process. By comparing observational data to the synthetic line profiles it is possible to determine these parameters. We tested this process to Brey 22 WR binary system, and applied to the enigmatic object of eta Carinae.
|
| | R.E. Stencel
Evidence for a precessing disk in the extreme binary, epsilon Aurigae.
Among the longest known eclipse durations and binary periods is that of the star epsilon Aurigae which exhibits 2 year long eclipses every 27.1 years. Oddly, the nature of the secondary in the system continues to elude ready identification. In 1965, Huang proposed a massive disk as the eclipsing body, and study of the 1984 eclipse led Lissauer and Backman to suggest an embedded B star binary in the disk to maintain it. A collaboration of observers allows me to present recent optical photometry and spectroscopy, near-IR spectroscopy and Spitzer space telescope IRS and MIPS observations of epsilon Aurigae as it approaches its next eclipse. These data argue for current detectability of the embedded binary, and precession of the disk axis, suggesting a radical change is possible for the next mid-eclipse brightening. An international monitoring campaign for the 2009-2011 is being organized, and participation invited via website http://www.du.edu/˜rstencel/epsaur.htm. |
| | Pavel Chadima
New Findings Supporting The Presence Of Various Structures Of The Circumstellar Matter In The Beta Lyr System
Introduction: Understanding large-scale mass exchange in binaries mainly requires studies of complicated objects in the rapid phases of the process. Beta Lyr is one of such objects. Methods: 52 photographic and 651 electronic spectra of beta Lyr were analyzed to obtain additional information about circumstellar matter. (1) The spectra were disentangled using the KOREL program. (2) Spectrophotometric quantities of 15 stronger absorption lines of the Roche lobe filling star were measured and corrected for the orbital continuum variations using the fluxes calculated from a fit of the light curves with the BINSYN program. Results: (1) Disentangling of photographic and electronic spectra led to the detection of weak absorption lines originating from the pseudophotosphere of the accretion disc. This way, a rich line spectrum of the accretion disc, not limited to only two previously known Si6347 and Si6371 lines, was obtained. A projected rotational velocity of 180km/s was estimated for the disc spectrum. Such a value agrees well with the assumption of the Keplerian rotation of the outer layers of the accretion disc. (2) After the correction, a pronounced increase of the strength of all absorption lines around phases of the primary eclipse was found. We argue that this is due to additional absorption of the light of the primary in one of the jets and/or scattering envelope above the accretion disc of the accreator. Discussion: All new findings support the current picture that the circumstellar structures of beta Lyr consist of a thick accretion disc, bipolar jets and a scattering envelope above the disk.
|
| Wednesday 23 August 2006 (afternoon sessions 7/8) |
|
Observing in the Era of Large-Scale Surveys
|
| 09:00-09:40 | D. Pourbaix (Belgium)
Binaries in Large-Scale Surveys
Even when a large-scale survey does not aim at finding binaries, its characteristics can sometime be changed into an efficient binary detector (e.g. Multi-band astrometry in SDSS). This talk will give a review of some (hopefully all) results related to binaries achieved with past and present large-scale surveys. In some cases, binaries pop up in a uniform dataset whereas, in other cases, binaries require the combination of 2+ surveys to be identified. |
| 09:40-10:20 | A. Prsa (Slovenia) & T. Zwitter (Slovenia)
Pipeline Reduction of Binary Light Curves from Large-Scale Surveys
One of the most important changes in observational astronomy of the 21st Century is a rapid shift from classical object-by-object observations to extensive automatic surveys. As CCD detectors are getting better and their prices are getting lower, more and more small and medium-size observatories are refocusing their attention to detection of stellar variability through systematic sky-scanning missions. This trend is aditionally powered by the success of pioneering surveys such as ASAS, DENIS, OGLE, TASS, their space counterpart Hipparcos and others. Such surveys produce massive amounts of data and it is not at all clear how these data are to be reduced and analysed. This is especially striking in the eclipsing binary (EB) field, where most frequently used tools are optimized for object-by-object analysis. A clear need for thorough, reliable and fully automated approaches to modeling and analysis of EB data is thus obvious. This task is very difficult because of limited data quality, non-uniform phase coverage and parameter degeneracy. The talk will review recent advancements in putting together semi-automatic and fully automatic pipelines for EB data processing. Automatic procedures have already been used to process the Hipparcos data, LMC/SMC observations, OGLE and ASAS catalogs etc. We shall discuss the advantages and shortcomings of these procedures and overview the current status of automatic EB modeling pipelines for the upcoming missions such as CoRoT, Kepler, Gaia and others. |
| 10:20-10:30 | T. Mazeh (Israel)
Reduction of eclipsing binary data in the Magellanic Clouds |
| 10:30-10:50 | D. Koch (USA)
The Kepler Mission and Binary Stars
The Kepler Mission is a photometric mission with a precision of 14 ppm ( at R=12) that is designed to continuously observe a single field of view (FOV) of greater 100 sq deg in the Cygnus-Lyra region for four or more years. The primary goal of the mission is to monitor >100,000 stars for transits of Earth-size and smaller planets in the habitable zone of solar-like stars. In the process, many eclipsing binaries (EB) will also be detected and light curves produced. To enhance and optimize the mission results, the stellar characteristics for all the stars in the FOV with R<16 will have been determined prior to launch. As part of the verification process, stars with transit candidates will have radial velocity follow-up observations performed to determine the component masses and thereby separate eclipses caused by stellar companions from transits caused by planets. The result will be a rich database on EBs. The community will have access to the archive for further analysis, such as, for EB modeling of the high-precision light curves. A guest observer program is also planned to allow for photometric observations of objects not on the target list but within the FOV, since only the pixels of interest from those stars monitored will be transmitted to the ground. |
| 10:50-11:05 | P.G. Niarchos (Greece), U. Munari (Italy), & T. Zwitter (Slovenia)
Evaluating with ground-based spectroscopy and Hipparcos photometry the Gaia contribution to the field of Eclipsing Binaries
During its definition phase, ESA's Cornerstone mission Gaia was design to perform extremely accurate photometry in 10 medium plus 5 broad bands and to collect about 90 epoch spectra with a resolving power of 11,500 and a wavelength range 8480-8740 Å (centered on the CaII triplet in the far red). Combining epoch photometry from the Hipparcos mission with ground-based spectra strictly simulating Gaia ones, we have investigated in a series of papers the performance expected from Gaia on SB2 EBs (Munari et al. 2001, Niarchos and Manimanis 2003, Zwitter et al. 2003, Marrese et al. 2004, Milone et al. 2005). We review here the results we obtained. The Gaia design is now under major revision, and its impact on EBs will be briefly addressed.
|
| 11:05-11:20 | T. Zwitter (Slovenia) and the RAVE team
The RAdial Velocity Experiment (RAVE)
RAVE is an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity) of several hundred thousand stars using the 6dF multi-object spectrograph on the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory. The spectra are obtained in the Ca-triplet near-IR region at a resolving power of R~7500. At present the first catalogue of 25.000 stars has been released (Steinmetz et al. 2006), with another 100.000 objects already observed and in the phase of data reduction and quality control. Issues regarding target selection and accuracy of the results will be discussed, and a special emphasis will be given to the potential of RAVE for the discovery and analysis of binary stars. |
|
Poster highlights 40 min
|
| | S.J. Thomas
Polaris: Mass and Multiplicity
Search and study of companions around Herbig Ae/Be stars
One of the most interesting constraints on the formation models comes from the study of multiplicity of young stars as a function of mass. While multiplicity studies of low mass T Tauri stars have been quite exhaustive, an unbiased and systematic investigation of multiplicity among Herbig Ae/Be stars is still lacking. We are therefore conducting a photometric and spectroscopic study of multiple systems among Herbig Ae/Be (HAEBE) stars, in order to first detect companions and then investigate their properties. The frequency and degree of multiplicity of HAEBE systems will provide new constraints on their formation mechanism.
Our program consists of: 1. high resolution AO imaging to detect close companions. We have data from about 80 stars obtained mainly with NIRI/Altair at Gemini but also with NACO at the VLT; 2. differential JHKL photometry of detected binaries to derive spectral energy distributions of the components of the systems; 3. near-infrared (NIR) spectroscopy to determine the spectral type of the companions.Our program has already measured NIR spectra of all southern candidates currently known and accessible with GNIRS (21). 4. BVRIJHK imaging (FOV=2.5' \& res. 0.8''), to study clustering around HAEBE stars.
The spectral information combined with the photometrically calibrated SEDs will allow us to determine the distance and extinction (thereby establishing physical association of companion) and, investigate the nature of the infrared excess in the secondary stars.
|
| | S Reffert
Multiplicity in a Complete Sample of Giant Stars
We have extensively monitored radial velocities of several hundred late-type giant stars at Lick Observatory for the past seven years. When the survey was started, the primary objective was a search for astrometric reference stars for SIM Planetquest. Since then the search for substellar companions has become the primary goal of this survey. The radial velocity precision is typically 5-8 m/s.
All stars were selected from the Hipparcos Catalogue, avoiding known binary stars where this was apparent from the information in the Hipparcos Catalogue. Nevertheless, a few known spectroscopic binaries slipped into our sample. Those were found very easily with just a few radial velocity measurements, and sometimes the spectroscopic orbits could be improved. Additionally, some new spectroscopic binaries were identified; for some of those, an orbit could be determined, while for others only lower limits on the period can be given at this point.
Here, we present some of our new spectroscopic orbits.
Furthermore, we determine the binary frequency of giant stars in a complete sample and compare it to the binary frequency of main-sequence stars.
|
| | D. Raghavan
A Multiplicity Survey of Solar-Type Stars in the Solar Neighbourhood
Stellar multiplicity is a fundamental astrophysical property. Apart from being the only physical basis for accurate mass determination, this parameter is believed to influence important processes such as planet formation. While early expectations indicated that multiple star systems are not suitable environments for planet formation, recent studies have shown that about 25% of the planetary systems reside in multiple star systems. Duquennoy & Mayor (1991, hereafter DM) is the seminal effort on stellar multiplicity of solar type stars. However, this work is quite dated, and even the basic sample of targets per their selection criteria has changed substantially. Using Hipparcos parallaxes, one finds that 135 stars fit DM’s sample selection criteria, while their sample, based on parallaxes in the Gliese catalogue, consisted of 164 primary stars.
Moreover, 35 targets of the updated sample were not included in the DM sample, showing that their sample excluded ~ 26% of the legitimate targets, and included ~ 40% that are now known to reside outside their volume limit. Furthermore, their study was primarily based on a single technique of companion detection – radial velocities.
We are working on a modern update to this seminal effort, selecting a volume limited sample using Hipparcos parallaxes. Our sample restricts targets to a B–V range of 0.5 – 1.0, parallax of greater than 40 mas (distance up to 25 pc), and within 2 magnitudes above or 1.5 magnitudes below the main sequence. These criteria result in the selection of 454 primary stars with total luminosity in the range of 0.1 – 10 LSun, giving us a physical basis of our definition of “solar type”. We are conducting a comprehensive multiplicity survey leveraging prior studies based on radial velocity, speckle, adaptive optics, interferometry, and common proper motion, and augmenting these with additional observations based on common proper motion detection for which companionship is confirmed by photometry, speckle, and long baseline interferometry. The details of our survey methods and some preliminary results will be presented at the IAU Symposium.
|
| | C. Maceroni
Close binaries in the CoRoT space experiment
The CoRoT satellite is planned for launch in the Fall of 2006. Its scientific goals are two core programs (asteroseismology and exo-planet search) and parallel science (Additional Programs).
CoRoT will have a strong impact on our understanding of close binaries, thanks to its high precision photometry (70 ppm) and continuous monitoring (150d) of the same field. Selected binary systems can be chosen, within the Additional Programs frame, as targets of long and continuous pointed observations. Moreover, the database of variable stars from the exo-planet search program will provide light-curves of prime quality for many thousand, mostly unknown, systems. This will allow for studies of fine effects on the light curves, of stellar activity and, in combination with ground-based observations, very accurate determination of fundamental stellar properties. Many new discoveries of interesting systems are expected, including those of low mass binaries. Besides, the mission will promote a quick development of the young field of asteroseismology in close binaries.
A different binary-related topic, crucial to the success of the mission, is that of handling background binaries, which, according to simulations, will be main source of false alarms in exo-planet detection.
The many aspects of binary-related research in CoRoT are coordinated by the "CoRoT Binary Thematic Team", which gathers the expertise and coordinates the work of scientists from the contributing countries.
|
| | R. Neuhaeuser
Astrometric imaging of the wide binary HD 19994 with a radial velocity planet candidate with sub-milli-arc-sec precision
We observed the 3 arc sec wide visual binary star HD 19994 twice with the VLT NACO AO instrument to measure the separation between the two stars with very high precision, in order to detect the astrometric wobble of star A due to its radial velocity planet Ab, to be measured as periodic change in the binary separation. We obtained roughly 100 short exposure images per epoch and could thereby obtain a relative astrometric precision in measuring the binary separation of below 100 micro arc sec. This is the best precision ever reached in ground-based single- aperture relative astrometry, comparable to a similar program with the HST FGS by Benedict et al. With this precision, it is possible to detect the astrometric wobble (or its upper limit) of star A due to its radial velocity planet as periodic change in the binary separation, to be observed in the next few years. With such a measurement, one can determine the mass of the spectroscopic companion, which is a planet candidate from radial velocity observations (m sin i, unknown orbit inclination i). Once such a project is shown to be successful for a known planet, one can start searching for new planets in binary stars. Such observations are also very useful for significantly improving the orbit of this and many other binaries.
|
| Thursday 24 August 2006 (morning sessions 9/10) |
|
II. Binary Stars as Critical Tools for obtaining direct and reliable information
|
|
The need to improve basic calibrations
|
| cancel | W. van Altena (USA)
A critical comparison of Hipparcos and earlier trigonometric parallaxes with those derived from astrometry, interferometry + spectroscopy, etc. |
| 09:00-09:30 | J. Aufdenberg (USA)
Interferometric Constraints on Gravity Darkening with Application to the Modelling of Spica A & B
In 2005 we obtained very precise interferometric measurements of the pole-on rapid rotator Vega (A0 V) with the longest baselines of the Center for High Angular Angular Resolution (CHARA) Array and the Fiber Linked Unit for Optical Recombination (FLUOR). For the analysis of these data, we developed a code for mapping sophisticated PHOENIX model atmospheres on to the surface of rotationally distorted stars described by a Roche-von Zeipel formalism. Given a set of input parameters for a star or binary pair, this code predicts the interferometric visibility, spectral energy distribution and high-resolution line spectrum expected for the system. For the gravity-darkened Vega, our model provides a very good match to the K-band interferometric data, a good match to the spectral energy distribution -- except below 160 nm -- and a rather poor match to weak lines in the high dispersion spectrum where the model appears overly gravity darkened. In 2006, we used the CHARA Array and FLUOR to obtain high precision measurements of the massive, non-eclipsing, double-line spectroscopic binary Spica, a 4-day period system where both components are gravity darkened rapid rotators. These data supplement recent data obtained with the Sydney University Stellar Interferometer. Our study follows the classic 1971 study by Herbison-Evans et al. who resolved Spica as a binary with the Narrabri Intensity Interferometer. We will report on our progress modelling the new interferometric and archival spectroscopic data, with the goal towards better constraining the apsidal constant.
|
| 09:30-09:50 | D. Valls-Gabaud (USA)
The distance to the Pleiades revisited
A review of the different methods used to measure the distance to the Pleiades will be presented, along with a detailed discussion on their uncertainties.
|
|
Increasing possibilities of classical methods: a few examples
|
| 09:50-10:20 | A. Gimenez (Spain)
A new look into the apsidal motion test of eclipsing binaries
Internal stellar structure for stars other than the Sun can only be studied in detail by means of well-detached double-lined eccentric eclipsing binaries. In this case we can determine accurate masses and radii for the component stars and evaluate the quadrupole distortion produced by rotation and tides, leading to the internal stellar density concentration. A review of the topic is presented together with new developments and problems identified. Furthermore, the measurement of the relativistic term in the apsidal motion is also critically assessed. |
| 10:20-10:50 | T. Henry (USA)
The Sun’s Smaller Cousins Are Running the Universe ---The Masses Of Red And Brown Dwarfs
Although not one red dwarf can be seen with the naked eye, they dominate the solar neighborhood, accounting for no less than 70% of all stars. The large numbers of these wee denizens of the night actually translate into a surprisingly large amount of mass -- in fact, more mass is found in M dwarfs than in any other stellar spectral type.
To determine just how important red dwarfs are to the nature of the Universe, an accurate mass-luminosity relation (MLR) must be determined so that a relatively easily determined characteristic, luminosity, can be converted into the critical parameter, mass.
Results from a decade-long observational effort to calibrate the MLR for red dwarfs using the Fine Guidance Sensors (FGSs) on the Hubble Space Telescope (HST) will be highlighted. For many of the binary systems targeted, the interferometric data from HST are combined with radial velocity data to further improve the mass measurements, which often have errors less than 5%. Related results from a large southern sky parallax program to determine accurate distances to red dwarfs, and a search for companions orbiting them, will also be discussed.
The state of mass determinations for M dwarfs’ smaller cousins, the L and T dwarfs, will also be reviewed. Although we do not yet know the size of the true population of these (primarily) substellar objects, only by mapping out the interplay of their masses and luminosities (which change drastically with time) can we understand their contribution to the mass budget of the Universe.
|
| 10:50-11:20 | B. Lane (USA)
|
| 11:20-11:40 | T. Oswalt (USA)
Fragile Binaries as Observational Leverage on "Difficult Astrophysical Problems"
Loosely bound, “fragile” binary stars, whose separations may reach ~0.1 pc, are like open clusters with two coeval components. They provide a largely overlooked avenue for the investigation of many astrophysical questions. For example, the orbital distribution of fragile binaries with two long-lived main sequence components provides limits on the cumulative effects of the Galactic environment. In pairs where one component is evolved, the orbits have been amplified by post-main-sequence mass loss, potentially providing useful constraints on the initial-to-final mass relation for white dwarfs. The nearly featureless spectra of cool white dwarfs usually provide little information about intrinsic radial velocity, full space motion, population membership, metallicity, etc. However, distant main sequence companions provide benchmarks against which those properties can be determined. In addition, the cooling ages of white dwarf components provide useful limits on the ages of their main sequence companions, independent of other stellar age determination methods. This talk will summarize how fragile binaries provide useful leverage on these and other problems of interest.
|
|
Poster highlights 30 min
|
| | A. Tokovinin (Chile) or N. Shatsky (Russia)
Direct measurement of tidal dissipation in very eccentric binaries
Considerable effort has been spent to date in measuring the period of tidal circularisation in close binaries as a function of age, in order to constrain the tidal dissipation theory. Here we evaluate a new, direct method of measuring the tidal dissipation by precise timings of periastron passages in a very eccentric binary. The example of the 41 Dra system is studied in some detail.
|
| | R. Roman
V477 Cygni – A Theoretical Approach Of The Apsidal Motion
The existence of various values for the apsidal period of V477 Cygni, a lack of the values for the apsidal motion constants and a suspicious presence of a third body in the binary system, have incited our interest for a new analysis of the apsidal motion. So, we adopted the assumption that both star components are main sequence stars. In such conditions, in Table 1 performed by Cisneros – Parra (1970), we have introduced the mean density, in order to facilitate the corresponding interpolation. Numerical computations lead to the apsidal constants: k21=0.0046, k22=0.0043 and U=377 years for the apsidal period. These results are not affected by an eventual presence of a third body. |
| | M.V. McSwain
Ejection of Runaway Binary Stars
The runaway O-type stars HD 14633 and HD 15137 are both SB1 systems that were probably ejected from the open cluster NGC 654 (Boyajian et al. 2005). Were these stars dynamically ejected by close gravitational encounters in the dense cluster, or did the binaries each receive a kick from a supernova in one member? We present new results from our investigation of the optical, UV, X-ray, and radio properties of these binary systems to discuss the probable ejection scenarios.
|
| Friday 25 August 2006 (morning sessions 11/12) |
|
Increasing possibilities of classical methods (continued)
|
| 09:00-09:20 | J. Chaname (Peru/USA)
Catalogues of Common Proper Motion Binaries: a Gold Mine for Galactic Studies
I review the construction of the largest catalog of genuine wide binaries (a > 100 AU) in the solar neighborhood available today. Each entry is cleanly classified as belonging to either the disk or the halo of the Galaxy. These samples are drawn from the revised New Luyten Two-Tenths (rNLTT) catalog of Salim & Gould and are complete to projected separations of 500 and 900 arcsec, corresponding to about 0.1 and 1 pc, respectively. I briefly review the main steps in their selection and classification, which make use of a variety of astrometric and photometric data. I then present the most important results derived from this wide-binary catalog, with implications on issues such as star formation in the early Galaxy, the nature of halo dark matter, the age of the stellar halo, and accurate geometric distances to low-mass field stars. Finally, I outline the prospects for using SDSS in the construction of a catalog of halo wide binaries which, by greatly improving the statistics at physical separations crucial for dark matter studies, will enable direct exploration of regimes of MACHO masses that are only marginally accessible, if at all, by the decades-long microlensing campaigns, particularly in the astrophysically important regime of heavy stellar remnants. |
|
Evolutionary models for binary and multiple stars
|
| 09:20-09:50 | C. Clarke (UK)
Progress in the theories of binary formation
theoretical simulations, impact of mass exchange on the chemistry of Galaxy, observational insights into binary star formation from statistics - distributions of a or P, M2/M1, e in various contexts and how these change as star populations age
|
| 09:50-10:20 | L. Kisseleva-Eggleton (USA) & P. Eggleton (USA)
Progress in the theories of binary evolution |
| 10:20-11:00 | D. Bisikalo (Russia) & T. Matsuda (Japan)
Testing and improving the dynamical theory of mass exchange
The study of the flow structure is of great importance, and the results can be used both for consideration of the evolution status of binary stars and for the interpretation of observational data. In this report we present the review of 3D gas dynamic models used for the description of the mass exchange in close binaries.
Main features of the flow structure in steady-state close binaries are summarized. It is shown that in self-consistent considerations the interaction between the stream from the inner Lagrangian point and the forming accretion disc is shock-free, and, hence, a "hot spot" does not form at the outer edge of the disc. To explain the presence of the observed zones of high luminosity in close binaries a self-consistent "hot line" model was proposed according to which excess energy is released in a shock wave formed due to interaction between the circumdisc halo and the stream. The "hot line" model was confronted with observations and confirmed by virtue of comparison of synthetic and observational light curves for cataclysmic variables and by the analysis of Doppler tomograms.
The special attention is paid at physics of accretion discs in binary systems and particularly at waves in discs. The possible observational manifestations of the "hot line" wave and two arms of the tidal shocks are discussed. We also suggest that an additional spiral density wave can exist in the inner parts of the cold accretion disc. This spiral wave is due to the retrograde precession of streamlines in the binary system. The results of 3D gas dynamic simulation have shown that a considerable increase in the accretion rate (by an order of magnitude) is associated with the formation of the ''precessional'' spiral wave. Basing on this fact we suggest a new mechanism for the superoutbursts and superhumps in close binaries.
|
| 11:00-11:20 | H. Zinnecker (Germany)
Young binaries as a test for pre-Main Sequence evolutionary tracks |
|
Poster highlights 20 min
|
| | A Derekas
Eclipsing binaries in the LMC: a wealth of data for astrophysical tests
We have analysed publicly available MACHO observations of 6833 variable stars in the Large Magellanic Cloud, classified as eclipsing binaries. After finding that a significant fraction of the sample was misclassified, we redetermined periods and variability class for all stars, producing a clean sample of 3031 eclipsing binaries. We have investigated their distribution in the period-color-luminosity space, which was used, for example, to assign a foreground probability to every object and establish new period-luminosity relations to selected types of eclipsing stars. The latter was used to test the existence of red giant contact binaries. We found that the orbital period distribution of LMC binaries is extremely similar to those of the SMC and the Milky Way. To fully utilize advantages of the MACHO database, we have also determined the rate of period change for every star. As a result, there is a significant increase in the number of known LMC binaries with apsidal motion (up to about 20), which offers an excellent sample to test theories of apsidal motion. We also discovered about 50 eclipsing binaries with cyclic period changes, suggesting the presence of a third companion. If confirmed, these systems will allow testing the effects of multiplicity in stars via modelling their orbital evolution. We also investigated the hypothesis of orbital period variations induced by mass-transfer in semidetached systems by a statistical analysis of the measured rates of period change. Finally, we discovered several eclipsing binaries with pulsating components, which offers a new way of studying oscillations in massive B-type stars through combining theories of stellar oscillations and binary star astrophysics.
|
| | S. Catalan
The Initial-to-final Mass Function of White Dwarfs in Common Proper Motion Pairs
The initial-to-final mass relationship is the connection between the mass of a white dwarf and the mass of its progenitor in the main sequence. This function is of paramount importance to aspects such as determining ages and distances of globular clusters, constraining the chemical evolution in galaxies, and also understanding the properties of the galactic population of white dwarfs. Despite its relevance, this relation is still poorly constrained. A promising approach to diminish the uncertainties is to study white dwarfs for which external constraints are available. This is the case of white dwarfs in common proper motion pairs. Important information of the white dwarf member can be inferred from the study of the companion, since they were born at the same time and with the same chemical composition.
We report new results obtained from spectroscopic observations of both members of several common proper motion pairs composed of a main sequence star (F, G or K type) and a white dwarf. From the fitting of the absorption lines to theoretical models we obtain the effective temperature and the surface gravity of the white dwarf member and, consequently, its mass and cooling time. The determination of the metallicity of the main sequence companion helps us to infer the metallicity of the progenitor of the white dwarf. This procedure allows us to estimate the main sequence lifetime of the white dwarf, and hence, to determine the total age of the system. At that point, we will be able to derive the mass of the main sequence progenitor of the white dwarf and to better establish the initial-to-final mass relationship.
|
|
III. Binary Stars as Critical Tests for studying specific phenomena
|
|
Binary stars as probes of our Galaxy
|
| 11:40-12:10 | D. Vanbeveren (Belgium)
Close Pairs as probes of the Galaxy’s Chemical Evolution
Understanding the galaxy in which we life is one of the great intellectual challenges facing modern science. With the advent of high quality observational data, the chemical evolution modeling of our galaxy has been the subject of numerous studies in the last years. However, all these studies have one missing element which is the “evolution of close binaries”. Unfortunately at present we know that the majority of the observed stars are members of a binary or multiple system. Therefore galactic studies that do not account for close binary evolution may be far from realistic.
About 6 years ago we (the Astrophysical Institute of the Vrije Universiteit Brussels) started a project to do chemical evolutionary simulations with the inclusion of detailed binary evolution. In the present paper we first give an overall review of the conclusions resulting from this study.
The second part of the papers deals with the puzzling temporal galactic evolution of 14N and the effects of very massive stars and binaries. Low metallicity very massive stars with an initial mass between 140 Mo and 260 Mo can be subdivided into two groups: those between 140 Mo and 200 Mo which produce a relatively small amount of Fe, and those with a mass between 200 Mo and 260 Mo where the Fe-yield ejected during the supernova explosion is enormous. We first demonstrate that the inclusion of the second group into a chemical evolutionary model for the Solar Neighborhood predicts an early temporal evolution of Fe which is at variance with observations whereas it can not be excluded that the first group could have been present. We then show that a low metallicity binary with very massive components (with a mass corresponding to the first group) can be an efficient site of primary 14N production through the explosion of a binary component that has been polluted by the pair instability supernova ejecta of its companion. When we implement these massive binary 14N yields in a chemical evolution model, we conclude that very massive close binaries may be important sites of 14N enrichment during the early evolution of the Galaxy.
|
| Friday 25 August 2006 (afternoon sessions 13/14) |
|
Binary stars as probes of our Galaxy (continued)
|
| 12:10-12:30 | C. Allen (Mexico)
Halo Wide Binaries and Moving Clusters as Probes of the Dynamical and Merger History of our Galaxy
Wide or fragile pairs are sensitive probes of the galactic potential, and they have been used to provide information about the galactic tidal field, the density of GMC and the amount of dark matter present in both the disk and the halo. Halo wide binaries and moving clusters, since they are likely to be the remains of past mergers or of dissolved clusters, can provide information on the dynamical and merger history of our Galaxy. Such remnants should continue to show similar motions over times of the order of their ages. We have looked for phase space groupings among the low-metallicity stars of Beers et al. (2000) and of Schuster et al. (2004) and have identified a number of candidate moving clusters. In several of the moving clusters from the data of Schuster et al. we found a wide CPM binary already identified in the catalogue of wide binaries among high-velocity and metal-poor stars of Allen et al. (2000). Spectroscopic follow-up studies of these stars would confirm the physical reality of the group, as well as allow us to distinguish whether their progenitors are dissolved clusters or accreted systems. The proper motions of the Beers et al. stars are too small to appear in the CPM binary searches so far conducted, but the members of the moving groups we have identified are prime candidates for such searches. |
| 12:30-12:40 | H. Abt (USA)
Observed Orbital Eccentricities
For binaries with periods of more than a few weeks, nearly all eccentricities from zero (circular) to nearly one (highly elliptical) are possible. What are the average characteristics and limiting values? I considered the 1169 spectroscopic and visual systems with known orbital elements and B0-M5 dwarf primaries. The average eccentricities as a function of orbital period show a very systematic behavior. For systems with periods greater than about 1000 days, all eccentricities are equally probable, showing that in the process of binary formation, no specific eccentricities are favored. It is well known that for periods of a few days, all systems have been circularized by tidal interactions. For periods between a few days and 1000 days, the mean eccentricities increase from zero to a mean asymptotic value of 0.5. The upper limiting eccentricities are 0.8 for periods of months, 0.7 for periods of weeks, and 0.3 for periods around one week. Double-lined binaries tend to have higher mean eccentricities than single-lined ones of the same periods in accord with Kepler's third law because they have greater total masses and hence larger separations. Systems with giant primaries have the same behavior except they are circularized for periods less than about 70 days. |
| 12:40-13:00 | A. Poveda (Mexico)
The Frequency Distribution of Semi-major Axis of Wide Binaries. Cosmogony and Dynamical Evolution
The frequency distribution f(a) of semi-major axis of double and multiple systems, as well as their eccentricities and mass ratios, contain valuable fossil information about the process of star formation and the dynamical history of the systems. In order to advance in the understanding of these questions, we have made an extensive analysis of the frequency distribution f(a) for wide binaries (a>25 AU) in the various published catalogues, as well as in our own (Poveda et al., 1994; Allen et al., 2000; Poveda & Hernandez, 2003). Based upon all these studies we have established that the frequency f(a) is function of the age of the system and follows Oepik’s distribution f(a) 1/a in the range of 100 AU < a < ac(t), where ac(t) is a critical semi-major axis beyond which binaries have dissociated by encounters with massive objects. We argue that the physics behind the distribution f(a) 1/a is a process of energy relaxation, analogous to that present in stellar clusters (secular relaxation) or in spherical galaxies (violent relaxation). The frequency distribution of mass ratios in triple systems as well as the existence of runaway stars, indicate that both types of relaxation are important in the process of binary and multiple star formation.
Poveda, A., Allen, C. & Hernandez, A.
|
|
Asteroseismology; Stellar Activity
|
| 13:00-13:30 | C. Aerts (Belgium)
Asteroseismology of close binary stars
In this talk, we overview the current status of asteroseismology of close binary stars. We present an overview of the occurrence of pulsating stars in close binaries and we point out why the binarity is an asset, but also a complication, in this research topic. Subsequently, we discuss some case studies of close binaries containing a pulsating component. We provide the key ingredients for their successful binary and seismic interpretation and point out the current shortcomings. We end with an overview of future prospects.
|
| 13:30-14:00 | K. Olah (Hungary)
The Influence of Binarity on Stellar Activity
It is well-known from surveys of various activity signatures on high number of active stars that those stars which are members of close binaries show higher degree of magnetic activity than single stars of similar types and with similar rotational rates. The first models of common magnetic fields of close binaries were constructed as early as in the mid-1980's, but not much theoretical work followed until the early 2000's. In this talk I briefly summarize the recent knowledge of the activity of stars in close binary systems. The emergence of flux tubes from the deeper layers of the active star, which are thought to be the sources of the observed activity, is affected by the tidal effects that breaks the rotational symmetry. Examples will be shown on stellar active longitudes with respect of the companion stars, at the quadratures and substellar points. The corotation latitudes and preferred spot latitudes will be compared as the observations and models reveal. |
|
Poster highlights 20 min
|
| | H. Korhonen
Active Longitudes And Flip-Flops In Binary Stars
In many active stars the spots concentrate on two permanent active longitudes which are 180 degrees apart. In some of these stars the dominant part of the spot activity changes the longitude every few years.
This so-called flip-flop phenomenon was first reported in the early 1990’s in the single, late type giant FK Com. Since then flip-flops have been reported also on binary stars, young solar type stars and the Sun itself. Even though this phenomenon has been detected on many different kinds of active stars, still less than ten stars are known to exhibit this effect. Therefore no statistically significant correlation between the stellar parameters and the flip-flop phenomenon can be carried out. Here we present results from investigation where we have studied the long-term photometry of several magnetically active RS CVn binaries to see whether or not they show permanent active longitudes and the flip-flop phenomenon. We find that it is very common for the active regions to occur on permanent active longitudes, and some of these stars also show clear flip-flop phenomenon.
|
| | A. Pigulski
Discovery of four Beta Cephei stars in eclipsing binary systems
In the course of a search for Beta Cephei stars among bright stars observed within the ASAS-3 project, we have discovered four eclipsing binary systems in which primary components are Beta Cephei-type pulsating stars. Two of them belong to a loose open cluster Stock 14.
All four stars are very attractive targets for the follow-up spectroscopy and multicolour photometry which will yield accurate parameters of the components. Subsequently their interiors could be probed by means of asteroseismology.
|
