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Title:
A Planetary Companion to γ Cephei A
Authors:
Hatzes, Artie P.; Cochran, William D.; Endl, Michael; McArthur, Barbara; Paulson, Diane B.; Walker, Gordon A. H.; Campbell, Bruce; Yang, Stephenson
Affiliation:
AA(Thüringer Landessternwarte, D-07778 Tautenburg, Germany ), AB(McDonald Observatory and Astronomy Department, University of Texas at Austin, Austin, TX 78712 ), AC(McDonald Observatory and Astronomy Department, University of Texas at Austin, Austin, TX 78712 ), AD(McDonald Observatory and Astronomy Department, University of Texas at Austin, Austin, TX 78712 ), AE(McDonald Observatory and Astronomy Department, University of Texas at Austin, Austin, TX 78712 ), AF(Physics and Astronomy Department, University of British Columbia, Vancouver, BC V6T 1Z4, Canada ), AG(BTEC Enterprises Limited), AH(Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 3P6, Canada )
Publication:
The Astrophysical Journal, Volume 599, Issue 2, pp. 1383-1394. (ApJ Homepage)
Publication Date:
12/2003
Origin:
UCP
Astronomy Keywords:
Stars: Planetary Systems, Stars: Individual: Constellation Name: γ Cephei A, Techniques: Radial Velocities
DOI:
10.1086/379281
Bibliographic Code:
2003ApJ...599.1383H

Abstract

We report on the detection of a planetary companion in orbit around the primary star of the binary system γ Cephei. High-precision radial velocity measurements using four independent data sets spanning the time interval 1981-2002 reveal long-lived residual radial velocity variations superposed on the binary orbit that are coherent in phase and amplitude with a period or 2.48 yr (906 days) and a semiamplitude of 27.5 m s-1. We performed a careful analysis of our Ca II H and K S-index measurements, spectral line bisectors, and Hipparcos photometry. We found no significant variations in these quantities with the 906 day period. We also reanalyzed the Ca II λ8662 measurements of Walker et al., which showed possible periodic variations with the ``planet'' period when first published. This analysis shows that periodic Ca II equivalent width variations were only present during 1986.5-1992 and absent during 1981-1986.5. Furthermore, a refined period for the Ca II λ8662 variations is 2.14 yr, significantly less than the residual radial velocity period. The most likely explanation of the residual radial velocity variations is a planetary-mass companion with Msini=1.7MJ and an orbital semimajor axis of a2=2.13 AU. This supports the planet hypothesis for the residual radial velocity variations for γ Cep first suggested by Walker et al. With an estimated binary orbital period of 57 yr, γ Cep is the shortest period binary system in which an extrasolar planet has been found. This system may provide insights into the relationship between planetary and binary star formation.
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