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Title:
Direct detection of exoplanet host star companion γ Cep B and revised masses for both stars and the sub-stellar object
Authors:
Neuhäuser, R.; Mugrauer, M.; Fukagawa, M.; Torres, G.; Schmidt, T.
Affiliation:
AA(Astrophysikalisches Institut, Universität Jena, Schillergässchen 2-3, 07745 Jena, Germany ), AB(Astrophysikalisches Institut, Universität Jena, Schillergässchen 2-3, 07745 Jena, Germany), AC(Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125, USA ; Division of Particle and Astrophysical Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan), AD(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA), AE(Astrophysikalisches Institut, Universität Jena, Schillergässchen 2-3, 07745 Jena, Germany)
Publication:
Astronomy and Astrophysics, Volume 462, Issue 2, February I 2007, pp.777-780 (A&A Homepage)
Publication Date:
02/2007
Origin:
EDP
Keywords:
instrumentation: adapive optics, binaries: spectroscopic, binaries: visual, planetary systems, star: individual: &gamma, Cep
DOI:
10.1051/0004-6361:20066581
Bibliographic Code:
2007A&A...462..777N

Abstract

Context: The star γ Cep is known as a single-lined spectroscopic triple system at a distance of 13.8 pc, composed of a K1 III-IV primary star with V = 3.2 mag, a stellar-mass companion in a 66-67 year orbit (Torres 2007, ApJ, 654, 1095), and a substellar companion with Mp sin i = 1.7 M_Jup that is most likely a planet (Hatzes et al. 2003, ApJ, 599, 1383). Aims: We aim to obtain a first direct detection of the stellar companion, to determine its current orbital position (for comparison with the spectroscopic and astrometric data), its infrared magnitude and, hence, mass. Methods: We use the Adaptive Optics camera CIAO at the Japanese 8 m telescope Subaru on Mauna Kea, Hawaii, with the semi-transparent coronograph to block most of the light from the bright primary γ Cep A, and to detect at the same time the faint companion B. In addition, we also used the IR camera Ω Cass at the Calar Alto 3.5 m telescope, Spain, to image γ Cep A and B by adding up many very short integrations (without AO). Results: γ Cep B is clearly detected on our CIAO and Ω Cass images. We use a photometric standard star to determine the magnitude of B after PSF subtraction in the Subaru image, and the magnitude difference between A and B in the Calar Alto images, and find an average value of K = 7.3 ± 0.2 mag. The separations and position angles between A and B are measured on 15 July 2006 and 11 and 12 Sept. 2006, B is slightly south of west of A. Conclusions: .By combining the radial velocity, astrometric, and imaging data, we have refined the binary orbit and determined the dynamical masses of the two stars in the γ Cep system, namely 1.40 ± 0.12 Mȯ for the primary and 0.409 ± 0.018 Mȯ for the secondary (consistent with being a M4 dwarf). We also determine the minimum mass of the sub-stellar companion to be Mp sin i = 1.60 ± 0.13 M_Jup.
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