Symposium S240
Wednesday 23 August 2006 (morning sessions 5/6) | ||
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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. |
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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. |
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15:30-16:00 | M. Richards (USA) |
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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. |
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16:30-17:00 | T. ten Brummelaar (Australia/USA) comments on the first half of the symposium |
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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. |
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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. |
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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. |
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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. |
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