Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.2401t&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #24.01; Bulletin of the American Astronomical Society, V
Astronomy and Astrophysics
Astronomy
Scientific paper
The bright K1 III-IV star Gamma Cephei has been reported previously to have a possibly substellar companion in a 2.5-yr orbit. It also has a stellar companion in a much wider orbit that has not been seen directly until now. Here we determine for the first time the three-dimensional orbit of the stellar companion accounting also for the perturbation from the closer object. The analysis combines 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 mass of the stellar companion is inferred to be about 0.36 solar masses (M4 dwarf) for an assumed primary mass of 1.18 solar masses (established from a careful reanalysis of its physical properties), and the orbit of Gam Cep B is eccentric (e = 0.41) and has a period of 66.8 yr. The star is expected to be about 6.4 mag fainter than the primary in the K band. The minimum mass of the closer companion is 1.43 Jupiter masses, but the inclination angle of its orbit is unknown. Taking advantage of the high-precision Hipparcos observations we are able to place a dynamical upper limit on this mass of 16.9 Jupiter masses at the 3-sigma confidence level, confirming that it is substellar in nature. SIM will be able to directly measure the wobble due to the planet and establish its mass unambiguously. Our work shows that its orbit (semimajor axis = 1.9 AU) 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. Partial support is acknowledged from NASA's MASSIF SIM Key Project (BLF57-04) and NASA Origins grant NNG04LG89G.
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