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A Program for the Analysis of Long-Period Binaries: The Case of ϒ Delphini

Published online by Cambridge University Press:  12 April 2016

Alan W. Irwin ,
Don A. VandenBerg  and
Ana M. Larson
Alan W. Irwin
Affiliation:
Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, Canada
Don A. VandenBerg
Affiliation:
Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, Canada
Ana M. Larson
Affiliation:
Department of Astronomy, University of Washington, Seattle, Washington, USA

Abstract

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Binary systems can be analyzed like clusters but with additional constraints from the orbit. The theories of stellar interiors and atmospheres are used to analyze the color-magnitude diagram and spectra to test the consistency of theory and observation and also to provide results on the distance, chemical composition, age, and individual masses, radii, and effective temperatures. Given the total mass resulting from the theoretical analysis, it is possible to determine the complete orbit of even long-period binaries if at least 6 components of the position, velocity and acceleration vectors have been observed.

For this paper we apply such a theoretical and orbital analysis to the ϒ Delphini binary consisting of a K1 IV primary (ϒ2 Del) and an F7 V secondary (ϒ1 Del). The primary has been observed with the preciseradial-velocity (PRV) technique and shows a radial acceleration of 2.2 ± 0.7 m s−1 yr−1 as well as a significant (false alarm probability < 0.01) periodic signature (P = 1.44 yr). At least three possible causes of this periodic signature are pulsation, rotation, or a planetary companion. The mass and radius results (M2 = 1.72M⊙, M1 = 1.57M⊙, R2 = 6.43R⊙, and R1 = 2.21R⊙) of our theoretical analysis help constrain the possibilities. The pulsational hypothesis requires more investigation of whether it is possible to excite a g-mode or an r-mode period that is much longer than the fundamental period of 0.5 dy derived from the mass-radius results. The rotational hypothesis leads to an inconsistency; the published value of υ sin i is a factor of 4.5 larger than the maximum value allowed by the radius and the PRV period of 1.44 yr. More investigation is required to determine whether increased macroturbulence and decreased υ sin i (by a factor of 4.5) is consistent with observed line profiles. From the PRV period and the primary mass a possible planetary companion would have υ sin i = 0.7 Jupiter masses with an orbital semimajor axis of 1.5 AU. The orbital results for the stellar binary (closest approach > 15 AU) shows there is room in the system for such a possible planetary companion of ϒ2 Del to survive the gravitational perturbations of ϒ1 Del.

Type
Part 8. Binary Stars
Information
International Astronomical Union Colloquium , Volume 170: Precise Stellar Radial Velocities , 1999 , pp. 297 - 307
Copyright
Copyright © Astronomical Society of the Pacific 1999

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