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A Visual-Spectroscopic Orbit for the Binary ∑248

Guillermo Torres
Publications of the Astronomical Society of the Pacific
Vol. 107, No. 712 (1995 June), pp. 524-530
Stable URL: http://www.jstor.org/stable/40680573
Page Count: 7
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
A Visual-Spectroscopic Orbit for the Binary ∑248
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Abstract

Spectroscopic studies of visual binaries with angular separations less than about 1" have so far had great difficulty in providing the individual radial velocities for the components, because of the small velocity differences that are typical in these systems. The recent introduction of TODCOR, a two-dimensional cross-correlation technique (Zucker and Mazeh, ApJ, 420, 806 1994), promises to change the situation, bridging the gap between the wider pairs resolvable at the telescope, and the classical double-lined spectroscopic binaries, with large velocity amplitudes. We present the first example of an application of TODCOR to such a case: the study of the close visual pair ∑248. We report our high-resolution low signal-to-noise spectroscopic observations of the system over the past seven years, which happen to cover the periastron passage. Using TODCOR, we are able to disentangle the light from the two stars in our composite spectra and obtain radial velocities for both components despite the small velocity difference. By combining our velocities with all available astrometric observations of the pair we derive for the first time a visual-spectroscopic orbital solution, with a period of about 310 yr. We obtain also the orbital parallax of the system, corresponding to a distance of 60 pc, as well as the individual masses, which are consistent with early K-type dwarfs.

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