2006/09/22 by Guillermo Torres · 2 citations
Physics and Astronomy · #Astro and Planetary Science #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Brown dwarf #Exoplanet #Metallicity #Minimum mass #Orbit (dynamics) #Orbital eccentricity #Physics #Planet #Planetary mass #Primary (astronomy) #Radial velocity #Star (game theory) #Stars #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/509715
published as Astrophys.J.654:1095-1109,2007 · 28 pages in emulateapj style, including tables and figures. Accepted for publication in ApJ
arxiv created 2006/09/22 · openalex publication_date 2007/01/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The bright, K1 III-IV star γ Cep has been reported previously to have a possibly substellar companion in a ~2.5 yr orbit, as well as an unseen stellar companion at a larger separation. We determine for the first time the three-dimensional orbit of the latter, accounting also for the perturbation from the closer object. We combine new and existing radial velocity measurements with intermediate astrometric data from the Hipparcos mission (abscissa residuals), as well as ground-based positional observations going back more than a century. The orbit of the secondary star is eccentric ( e = 0.4085 ± 0.0065) and has a period P = 66.8 ± 1.4 yr. We establish the primary star to be on the first ascent of the giant branch and to have a mass of 1.18 ± 0.11 M ☉ , an effective temperature of 4800 ± 100 K, and an age around 6.6 Gyr (for an assumed metallicity [Fe/H] = +0.01 ± 0.05). The unseen secondary star is found to be an M4 dwarf with a mass of 0.362 ± 0.022 M ☉ and is expected to be ~6.4 mag fainter than the primary in K . The minimum mass of the putative planetary companion is M p sin i = 1.43 ± 0.13 M Jup . Based on high-precision Hipparcos observations, we are able to place a dynamical upper limit on this mass of 13.3 M Jup at the 95% confidence level, and 16.9 M Jup at the 99.73% (3 σ) confidence level, thus confirming that it is indeed substellar in nature. The orbit of this object is only 9.8 times smaller than the orbit of the secondary star (the smallest ratio among exoplanet host stars in multiple systems), but it is stable if coplanar with the binary.