Additional Abstracts

Listed below are a few abstracts not officially submitted to the IAU.


Observed Orbital Eccentricities
Author: Helmut A. Abt (Kitt Peak National Observatory, Tucson, AZ USA)
Abstract: 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.

Interferometry with single telescopes
Author: Yuri Balega (Russia)
Abstract: visible and IR speckle interferometry, adaptive optics, HST FGS, other single-aperture techniques

Progress in the theories of binary formation
Author: C. Clarke (UK)
Abstract: 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

Progress in the theories of binary evolution
Author: L. Kisseleva-Eggleton (USA) & P. Eggleton (USA)
Abstract: none submitted

The UV Spectrum of the Binary Star 88 Her: Activity Cycles in the Circumstellar Envelope
Author: Anahi Granada
Abstract: Since its discovery as a variable star, 88 Her has undergone three long-term photometric variation cycles with transitions between Be-shell and normal B phases. From the spectroscopic study of fifteen high resolution spectra obtained by the IUE satellite between 1981 and 1992 we were able to set parameters such as optical depths and location of line forming regions. We also found that the periodic radial velocity variations of UV Fe II lines agree with the orbital period of the binary system of 86.7 days (Harmanec et al, 1974) and that their residual intensity variations have a cycle of about 1560 days. Our aims are to relate the properties of the circumstellar envelope of 88 Her to the spectroscopic variability observed in Fe II and Mg II lines, and to understand the mechanisms which cause them, as well as the influence that binarity has on them.

Algols contribute to the interstellar mass
Authors: Jean-Pierre DE GREVE, Camiel DE LOORE, Walter VAN RENSBERGEN, Research-unit: ASTRO, Vrije Universiteit Brussel, Vrije Universiteit Brussel, Belgium
Abstract: We revisited analytical expressions for the distribution of orbital periods and mass ratios for non-evolved binaries with a B type primary. Selection effects governing the observations were taken into account in order to compare theory with observations. Theory was optimized so as to fit best with the observed P- and q-distributions of non-evolved SB1s and SB2s. The accuracy of the theoretical mass ratio distribution function is severely hindered by the uncertainties on the observations. Our further computations compare statistically the observed distributions of orbital periods and mass ratios of Algols with those obtained from the Brussels binary evolutionary code. Conservative Roche Lobe Over Flow (RLOF) reproduces the observed distribution of orbital periods but fails to explain the observed mass ratios in the range q  [0.4-1]. In order to obtain a better fit the binaries have to lose a significant amount of matter, without losing too much angular momentum. We tested the following binary evolutionary scenario: The mass acquired by the gainer during RLOF enhances the rotational velocity of the latter. Tidal forces counteract this acceleration. Both mechanisms may speed up the equatorial velocity of the gainer close to its critical value. The luminosity of the gainer is amplified with the accretion luminosity in the equatorial region. Only during a short tine lapse of rapid RLOF spinning-up and accretion luminosity act together to remove mass and angular momentum from the gainer and blow it into the interstellar medium. Consequently also Algols enrich the ISM. The binaries persist for a longer time with a larger mass ratio compared to conservative evolution. Since the mass is blown away from the gainer as an enhanced stellar wind not much angular momentum leaves the system; hence the obtained distribution of the orbital periods of Algols differs not very much from those obtained with the conservative scenario. The proposed time-dependent liberal scenario reproduces the observed distributions of mass ratios and orbital periods of Algols better than conservative evolution would do.

Closing comments and thanks
Author: W. Hartkopf (USA)
Abstract: a few thank yous, etc.

Accelerating binaries near the Sun and far away
Author: V. Makarov (USA)
Abstract: Most binary stars have orbital periods longer than a few years. Binarity of such systems is difficult to detect spectroscopically through short-term radial velocity monitoring. As far as visual binaries are concerned, even the largest space- and ground-based telescopes are limited in resolving capabilities to the most long-period gravitationally bound systems with small magnitude differences, barring a relatively small number of nearest stars. Systems that exhibit nonlinear apparent motion on the sky belong to the important, poorly explored category of intermediate period (6 - 100 yr) binaries in a wide range of mass ratios. The recently published lists of accelerating stars, based on Hipparcos and Tycho-2 astrometric data, allow us to investigate statistical correlations of binarity with other basic stellar properties, e.g., mass, age, chromospheric and coronal activity and spectral peculiarities. The sample of accelerating stars is explored for three important categories of binaries. The first category includes nearby (D < 100 pc) stars that are likely to be younger than the Pleiades (~100 Myr). Many of these stars appear to be members of sparse, loosely co-moving groups, whose origins and conditions of formation are unknown. The physical conditions of the natal star forming regions are imprinted in the binary statistics and the initial mass function. The second type of accelerating stars of special interest are the nearest late K and M dwarfs and cool white dwarfs, whose dim companions can be substellar objects or very late M dwarfs. This study is expected to eventually shed light on the existence of the brown dwarf desert in the domain of long periods and low primary mass. Finally, the presence of strongly accelerating dwarfs and giant stars at large distances (D > 1 kpc) in the Hipparcos catalog deserves careful study. It implies existence of systems with massive, but dim companions. Stars with masses above 8 Msun may constitute a few percent of all stellar population in rich open clusters, and owing to their short lifetimes, neutron stars and low-mass black holes may be fairly common in binary systems. In distant accelerating binaries, we may have the long-period counterparts to low-mass X-ray binaries (LXMB), which have orbital periods of a few hours to several days.

Looking for Exoplanet Transits in Bright Stars with Small Field-of-View Detectors
Author: Eder Martioli (Brazil)
Abstract: Differential photometry is a robust technique for ground-based observations of transits since it sorts out slow variations of sky transparency as well as other first order effects that are common to all stars in the field-of-view (FOV) of the imaging detector. To work properly, differential photometry has a few requirements like similar brightness of the target and reference stars, similar colours and a relative proximity in the plane of the sky to avoid sensitivity variations like those caused by vignetting in the FOV. It happens that for bright stars these conditions are hardly met. Typical CCDs in a ~60 cm class telescope give a FOV of ~10 arcmin and this is not enough to have in the same image frame suitable reference stars. Also, bright (V < 7) tend to saturate the detector for the shortest practical integration time. To minimize these problems, we tested an instrumental setup in which half of the detector is covered with a neutral density (D=2.3) filter. We report CCD observations on which we achieved milimagnitude precision for bright systems that are not known to show transits, like Tau Boo, 55 Cnc and HD 162020, as well as the well known case of HD 209458.

Reduction of eclipsing binary data in the Magellanic Clouds
Author: T. Mazeh (Israel)
Abstract: none submitted

Summary Talk #1
Author: C. Scarfe (Canada)
Abstract: comments on the first half of the symposium

GL 569 B: A Brown Dwarf Triple?
Authors: M. Simon (SUNY-Stony Brook), C. Bender (SUNY-Stony Brook), & L. Prato (Lowell Obs.)
Abstract: We report the results of high spectral and angular resolution infrared observations of the multiple system GL 569 A and B that were intended to measure the dynamical masses of the brown dwarf binary believed to comprise GL 569 B. Our analysis did not yield this result but, instead, revealed two surprises. First, at age ∼ 100 Myr, the system is younger than had been reported earlier. Second, our spectroscopic and photometric results provide support for earlier indications that GL 569 B is actually a hierarchical brown dwarf triple rather than a binary. Our results suggest that the three components of GL 569 B have roughly equal mass, ∼ 0.04 Msun.

Reducing data from long-baseline interferometers
Author: Theo ten Brummelaar (Australia/USA)
Abstract: Processing long-baseline interferometry data presents a unique set of complications: How does one derive relative astrometry when one or both components is resolved? How can 1-D interferometric results be used to solve a 2-D orbit? How can baseline-only solutions be combined with historical data and how should older baseline data be published so that they can be combined with later interferometric data?

Direct measurement of tidal dissipation in very eccentric binaries
Authors: A. Tokovinin (Chile) & N. Shatsky (Russia)
Abstract: 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.

Summary Talk #2
Author: V. Trimble (USA)
Abstract: comments on the second half of the symposium

A critical comparison of Hipparcos and earlier trigonometric parallaxes with those derived from astrometry, interferometry + spectroscopy, etc.
Author: W. van Altena (USA))
Abstract: none submitted

Young binaries as a test for pre-Main Sequence evolutionary tracks
Author: Hans Zinnecker (Germany)
Abstract: none submitted

The RAdial Velocity Experiment (RAVE)
Authors: Tomaz Zwitter (Univ. of Ljubljana, Slovenia) and the RAVE team
Abstract: 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.