J. A. Docobo

Tracing the young massive high-eccentricity binary system

Context. The nearby high-mass star binary system θ 1 Ori C is the brightest and most massive of the Trapezium OB stars at the core of the Orion Nebula Cluster, and it represents a perfect laboratory to determine the fundamental parameters of young hot stars and to constrain the distance of the Orion Trapezium Cluster. Aims. By tracing the orbital motion of the θ 1 Ori C components, we aim to refine the dynamical orbit of this important binary system. Methods. Between January 2007 and March 2008, we observed θ 1 Ori C with VLTI/AMBER near-infrared (H -a ndK-band) longbaseline interferometry, as well as with bispectrum speckle interferometry with the ESO 3.6 m and the BTA 6 m telescopes (B � and V � -band). Combining AMBER data taken with three different 3-telescope array configurations, we reconstructed the first VLTI/AMBER closure-phase aperture synthesis image, showing the θ 1 Ori C system with a resolution of ∼2 mas. To extract the astrometric data from our spectrally dispersed AMBER data, we employed a new algorithm, which fits the wavelength-differential visibility and closure phase modulations along the H -a ndK-band and is insensitive to calibration errors induced, for instance, by changing atmospheric conditions. Results. Our new astrometric measurements show that the companion has nearly completed one orbital revolution since its discovery in 1997. The derived orbital elements imply a short-period (P ≈ 11.3 yr) and high-eccentricity orbit (e ≈ 0.6) with periastron passage around 2002.6. The new orbit is consistent with recently published radial velocity measurements, from which we can also derive the first direct constraints on the mass ratio of the binary components. We employ various methods to derive the system mass (Msystem = 44 ± 7 M� ) and the dynamical distance (d = 410 ± 20 pc), which is in remarkably good agreement with recently published trigonometric parallax measurements obtained with radio interferometry.

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This article studies the existence of periodic Keplerian orbits for visual double stars whose corresponding apparent orbits are to pass through three selected points. The analytical results provide the basis for a new method of calculating orbits which does not require prior calculation of the areal constant. This method is applied to the binary 04404 N 4313.

Orionis C through periastron passage

First visual orbits for the binary T Tauri stars V773 Tau, FO Tau, and FS Tau and revised orbits for DF Tau and GG Tau are presented. The orbits are determined from a compilation of previous high spatial resolution imaging measurements and new astrometric measurements from the Calar Alto 3.5 m telescope. The orbital solutions, which must be considered preliminary because of the short orbital arcs observed, are used in combination with distance estimates to determine the dynamical masses for all five systems. The total mass of the triple system V773 Tau (whose primary is a K2+K5 spectroscopic binary) is 3.20 ± 0.71 M☉, and the masses of the four binary pairs range from 0.77 to 1.22 M☉. The orbital solutions for these systems predict projected relative orbital velocities that range from 0.1 to 13.4 km s-1 (2002 epoch); the majority are spectroscopically measurable if spatially resolved. Of particular interest is the GG Tau binary, which has a mass that is consistent with the value determined from circumbinary disk kinematics and an orbit that is coplanar with this disk. The stellar properties of the components of these five systems are determined from spatially resolved optical measurements, assuming dwarflike colors and a dwarflike temperature scale. With luminosity and temperature estimates, theoretical masses are determined from the predictions of four pre-main-sequence evolutionary models and compared with the dynamically determined values as a test of these models. Of the models tested, those of Palla & Stahler and Siess, Dufour, & Forestini predict masses that are the most consistent (within 1 σ) with the dynamical values over the component mass range of ~0.3-1.5 M☉. All models support coeval formation of these binaries.

ON THE ANALYTIC CALCULATION OF VISUAL DOUBLE STAR ORBITS

Orbital binary stars are essential objects for determining dynamical and physical properties of stars through a combined analysis of photometric and astrometric data. We compiled a set of orbital binaries with known trigonometric parallaxes and orbits of high quality, using data from current versions of the Catalogue of Orbits and Ephemerides of Visual Double Stars and the Sixth Catalog of Orbits of Visual Binary Stars as well as including updated information from WDS and SIMBAD. We constructed distributions of orbital binaries among dynamical mass, period, semi-major axis, and eccentricity of systems, which characterize the set. Some problems related to the parameterization of orbital binaries are also discussed in the paper.

Preliminary Orbits and System Masses for Five Binary T Tauri Stars

Results of the EMCCD-based speckle interferometric observations and differential photometry for 46 visual binaries obtained in 2007 June and July with the 6 m telescope of the Special Astrophysical Observatory (Russia) are presented. First preliminary orbits for COU 401, COU 1281, and COU 1037 as well as improved orbits for CHR 137, COU 100, COU 1136, COU 798, CHR 51, CHR 55, COU 315, COU 206, and ADS 13961, along with their dynamical mass estimates, are reported. On the basis of dynamical parallax information, first distance estimates for COU 100, COU 1136, COU 798, COU 206, and COU 1037 are calculated.

Dynamical masses of a selected sample of orbital binaries

We proposea methodologyfor analyzing triplestellar systemsthat include avisual double star whereinoneofthecomponents is a single- or double-lined spectroscopic binary. By using this methodology, we can calculate the most probable valuesof thespectroscopicbinary’sinclination, theangularseparation betweenits components,andits stellar masses, and wecanevenestimatethespectraltypes.ForafewWUMaYtypeeclipsingbinaries,stellarradiiarealsodetermined.Moreover, we present new formulae for calculating stellar masses depending on spectral type. In this way we have studied 61 triple systems, five of them W UMaYtype eclipsing binaries with low-mass subcomponents. In addition, we study nine quadruplesystems,applyingthesamemethodologyandconsideringthem twiceasatriplesystem.Withtheaim of having more accurate orbital elements, we have taken advantage of the occasion to calculate and improve orbits. In this way we have used a new speckle measurement to improve the orbital elements for the binary Hu 506 AB. Also, new visual orbits are calculated for the binaries BAG 10 Aa and LAB 6 Aa. Finally, we give a list of five spectroscopic binaries with more than 0B1 for the maximum angular separation; these should be easily observable as visual binaries by means of interferometric techniques. Subject headingg binaries: close — binaries: eclipsing — binaries: spectroscopic — binaries: visual — methods: data analysis — methods: statistical — stars: fundamental parameters

EMCCD SPECKLE INTERFEROMETRY WITH THE 6 m TELESCOPE: ASTROMETRIC MEASUREMENTS, DIFFERENTIAL PHOTOMETRY, AND ORBITS

This paper presents revised orbits and system masses of 14 visual double stars, in all of which at least one component is of early spectral type: WDS 00546+1911 (STT 20 AB), WDS 01040+3528 (HO 213), WDS 02039+4220 (STT 38 BC), WDS 03503+2535 (STT 65), WDS 06393+4200 (STT 150), WDS 08285-0231 (A551 AB), WDS 15088-4517 (SEE 219 AB), WDS 15416+1940 (HU 580 AB), WDS 16514+0113 (STT 315), WDS 17104-1544 (BU 1118 AB), WDS 19172-6640 (GLE 3), WDS 19411+1349 (KUI 93), WDS 22241-0450 (BU 172 AB), and WDS 23382+5514 (A1493). Star masses were calculated from Hipparcos parallax data whenever the precision was good enough (10 cases); otherwise, dynamical parallaxes were used, except in one case involving component multiplicity. Other physical and orbital properties of these stars are also discussed.

A Methodology for the Description of Multiple Stellar Systems with Spectroscopic Subcomponents

Results of speckle measurements and differential photometry carried out with the 6 m telescope of the Special Astrophysical Observatory (Russia) at the end of 2004 are presented. One new (COU 1569) and four improved orbits (ADS 440AC, ADS 1729, ADS 5726, and COU 1897), as well as their dynamical mass estimates, are reported.

Orbits and System Masses of 14 Visual Double Stars with Early-Type Components

On the basis of slit spectra obtained with the SCORPIO spectral camera attached to the 2.6 m telescope of the V. Ambartsumian Byurakan Astrophysical Observatory (Armenia), MK classifications for 30 visual binaries comprising mostly late K and M type stars are presented. Comparison with other determinations shows that this configuration provides a reliable MK classification. Dynamical masses for 25 systems are computed. Using standard mass-luminosity calibrations, individual mass sums for 11 pairs consisting of virtually single, nonvariable dwarfs are calculated, showing a good agreement with corresponding dynamical masses. The dynamical parallax of HIP 112354 is closer to the trigonometric parallax given in the Yale General Catalogue of Trigonometric Stellar Parallaxes (van Altena et al.) than to the Hipparcos parallax.

Speckle Measurements and Differential Photometry of Visual Binaries with the 6 Meter Telescope of the Special Astrophysical Observatory

In this article we present the orbits and masses of 20 double stars discovered by P. Couteau at the Nice Observatory (France), namely WDS 01450+2703 (COU 750), 03321+4340 (1688), 03423+3141 (691), 06503+2409 (768), 12409+2708 (596), 14138+3059 (606), 15390+2545 (612), 16584+3943 (1289), 17075+3810 (1291), 17221+2310 (415), 18035+ 4032 (1785), 18043+4206 (1786), 19089+3404 (1462), 19180+2012 (321), 20151+3742 (2416), 20216+1930 (327 AB), 21593+4606 (2138), 22077+2622 (537), 22307+1758 (234) and 23199+2844 (439). For two of these stars, COU 750 and COU 1289, these are the first orbits to be published other than IAU Circulars; for the others, previously published orbits are improved on by those presented here. Star masses were in fifteen cases calculated from Hipparcos parallax data, and in the other five from dynamical parallaxes; in all cases, the error is estimated. Some of the other physical and orbital properties of these stars are also discussed.