October
2026
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2026AJ....172..242V
Authors
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Van Zandt, Judah
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Bowler, Brendan P.
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Endl, Michael
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Cochran, William D.
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MacQueen, Phillip
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Hatzes, Artie
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Torres, Guillermo
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Latham, David W.
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Howard, Andrew W.
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Fulton, Benjamin
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Isaacson, Howard
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Liu, Michael C.
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Walker, Samuel A. U.
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Xuan, Jerry W.
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Zhang, Jingwen
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Armendariz, Rebeca E. Soto
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Biddle, Lauren I.
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Franson, Kyle
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Jiang, Lillian
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Morgan, Marvin
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Tran, Quang H.
Abstract
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The γ Cephei system hosts one of the first exoplanets discovered and is orbited by one of the closest known stellar companions to a planet-hosting star. In this work, we derive updated orbital fits for γ Cep AB, the stellar binary, and Ab, the planet, by combining literature data with Hipparcos--Gaia astrometry, new radial velocities (RVs), and adaptive optics imaging. We acquired 328 RVs of γ Cep A with Keck/HIRES, AFP/Levy, McDonald/Tull, and Whipple/TRES, and eight adaptive optics imaging epochs with Keck/NIRC2, including the earliest spatially resolved image of γ Cep B in 2003. These observations extend the precision RV baseline of γ Cep to 45 yr and the direct imaging baseline to 23 yr, improving the inferred orbital parameter precision by a factor of 2--10 compared to previous work. For γ Cep B, we derive a semimajor axis of aB = 20.07 ± 0.06 au, a mass of MB = 415 ± 2 MJup (0.396 ± 0.002 M⊙), an eccentricity of eB = 0.422 ± 0.002, and an inclination of iB = 119 .° 8 ± 0 .° 1. For γ Cep Ab, we find a semimajor axis of aAb = 1.978 ± 0.007 au, a minimum mass of MAbsini=1.62-0.04+0.04MJup , and an eccentricity of eAb=0.07-0.03+0.03 . The system is dynamically compact, and its orbital architecture is consistent with von Zeipel--Lidov--Kozai (vZLK) oscillations, although the planet's orbital inclination remains insufficiently constrained to determine whether the vZLK mechanism is active. Using the RV residuals and dynamical constraints, we rule out additional Jovian companions between 2.5 and 20 au, and companions more massive than Neptune for a < 1 au, both at >90% confidence. The absence of additional giant planets over a broad range of orbital separations is consistent with a dynamically sculpted system in which the close stellar companion has strongly limited the formation or long-term survival of other long-period giant companions.
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