The Planet Host Star γ Cephei: Physical Properties, the Binary Orbit, and the Mass of the Substellar Companion

摘要: The bright, K1 III-IV star γ Cep has been reported previously to have a possibly substellar companion in ~2.5 yr orbit, as well an unseen stellar at larger separation. We determine for the first time three-dimensional orbit of latter, accounting also perturbation from closer object. combine new and existing radial velocity measurements with intermediate astrometric data Hipparcos mission (abscissa residuals), ground-based positional observations going back more than century. secondary is eccentric (e = 0.4085 ± 0.0065) period P 66.8 1.4 yr. establish primary be on ascent giant branch mass 1.18 0.11 M☉, effective temperature 4800 100 K, age around 6.6 Gyr (for assumed metallicity [Fe/H] +0.01 0.05). found M4 dwarf 0.362 0.022 M☉ expected ~6.4 mag fainter K. minimum putative planetary Mp sin i 1.43 0.13 MJup. Based high-precision observations, we are able place dynamical upper limit this 13.3MJup 95% confidence level, 16.9MJup 99.73% (3 σ) thus confirming that it indeed nature. object only 9.8 times smaller (the smallest ratio among exoplanet host stars multiple systems), but stable if coplanar binary.