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The ELODIE Survey for Northern Extra-Solar Planets IV

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The ELODIE Survey for Northern Extra-Solar Planets IV A&A 479, 271–275 (2008) Astronomy DOI: 10.1051/0004-6361:20078908 & c ESO 2008 Astrophysics The ELODIE survey for northern extra-solar planets IV. HD 196885, a close binary star with a 3.7-year planet A. C. M. Correia1,2,S.Udry2,M.Mayor2, A. Eggenberger3,2,D.Naef4,J.-L.Beuzit3, C. Perrier3, D. Queloz2,J.-P.Sivan5,F.Pepe5,N.C.Santos6,2, and D. Ségransan5 1 Departamento de Física da Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal e-mail: [email protected] 2 Observatoire de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland 3 Laboratoire d’Astrophysique de Grenoble, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France 4 European Southern Observatory, Casilla 19001, Santiago 19, Chile 5 Laboratoire d’Astrophysique de Marseille, Traverse du Siphon BP 8, 13376 Marseille Cedex 12, France 6 Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal Received 23 October 2007 / Accepted 28 November 2007 ABSTRACT Aims. We aim to significantly increase the number of detected extra-solar planets in a magnitude-limited sample to improve our knowledge of their orbital element distributions and thus obtain better constraints for planet-formation models. Methods. Radial-velocity data were taken at Haute-Provence Observatory (OHP, France) with the ELODIE echelle spectrograph. Results. We report the presence of a planet orbiting HD 196885 A, with an orbital period of 1349 days. This star was previously sug- gested to host a 386-day planet, but we cannot confirm its existence. We also detect the presence of a stellar companion, HD 196885 B, and give some constraints on its orbit. Key words. stars: individual: HD 196885 A – stars: individual: HD 196885 B – stars: binaries: visual – stars: planetary systems – techniques: radial velocities – methods: observational 1. Introduction companions, in particular with orbital periods around 368 days. Last section is devoted to our conclusions. The ELODIE Planet Search Survey was an extensive radial- velocity northern survey of dwarf stars at the Haute-Provence Observatory (OHP, France) using the ELODIE high-precision 2. HD 196885 A stellar characteristics fiber-fed echelle spectrograph (Baranne et al. 1996) mounted at the Cassegrain focus of the 1.93-m telescope. It started to operate HD 196885 A was observed by the HIPPARCOS astrometric at the end of 1993 and acquired data until the summer of 2006, satellite (HIP 101966). A high-precision spectroscopic study of when it was replaced by the new echelle spectrograph SOPHIE this star was also performed by Sousa et al. (2006) in order (Bouchy & The Sophie Team 2006). to examine the metallicity distribution of stars hosting planets. This survey is part of a large effort aimed at an extra-solar This star was also studied by near-infrared survey with adap- planet search through radial-velocity measurements, in order to tive optics of faint circumstellar environments, sensitive to com- characterize the types of exoplanets and to bring strong con- panions within the stellar and the sub-stellar domains (Chauvin straints on their processes of formation and evolution. ELODIE et al. 2006, 2007). Observed and inferred stellar parameters from was responsible for finding many extra-solar planets, among these different sources are summarized in Table 1. them the first hot Jupiter, 51 Peg b (Mayor & Queloz 1995). In the HIPPARCOS catalogue, HD 196885 A is given a spec- The original sample consisted of 142 stars, but a new sample tral type F8 IV, a visual magnitude V = 6.398 and a color in- of 330 stars was defined in 1997. Details of the program and the dex B − V = 0.559. The measured parallax (30.31 ± 0.81 mas) surveyed sample can be found in Perrier et al. (2003). leads to a distance of 33.0 ± 0.9 pc and an absolute magnitude In this paper we present the detection of two bodies around of MV = 3.8 ± 0.1. From CORALIE spectra, Sousa et al. (2006) the star HD 196885 A, one in the mass range of planets and the derivedaneffective temperature Teff = 6340 ± 39 K, a gravity other believed to be a stellar companion. This star was previously log g = 4.46±0.02 and a high metal content [Fe/H] = 0.29±0.05 described to harbor a planet with a period of about 386 days (al- (Table 1). The bolometric correction (BC = −0.006) is com- though no published reference is known), but we could not con- puted from Flower (1996) using the spectroscopic Teff determi- firm its presence in our observations (our analysis shows a planet nation. The bolometric magnitude is then MBol = 3.791, which with an orbital period of about 1349 days instead). The stellar allows us to derive a stellar luminosity of L = 2.40 L. Sousa companion was also recently observed using NACO adaptative et al. (2006) also computed the mass, M = 1.33 M, from optics by Chauvin et al. (2006, 2007). The stellar properties of evolutionary tracks using Geneva models (Schaller et al. 1992; HD 196885 A are briefly recalled in Sect. 2 and the radial veloc- Schaerer et al. 1993). From the B − V value and ELODIE cor- ities with the two detected companions are described in Sect. 3. relation functions we find v sin i = 7.3 ± 1.5[kms−1], meaning In Sect. 4 we discuss the possibility of the existence of more that the star is rotating fast. However, its measured activity level Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20078908 272 A. C. M. Correia et al.: HD 196885, a close binary star with a 3.7-year planet HD 196885A ELODIE + CORALIE Table 1. Observed and inferred stellar parameters for HD 196885 A. -30.1 ELODIE -30.15 CORALIE Parameter HD 196885 A Spectral Type F8 V -30.2 V 6.398 -30.25 − ± B V 0.559 0.006 -30.3 π [mas] 30.31 ± 0.81 d [pc] 33.0 ± 0.9 -30.35 -30.4 MV 3.8 ± 0.1 BC −0.006 Radial velocity [km/s] -30.45 MBol 3.79 -30.5 L [L]2.40 [Fe/H] 0.29 ± 0.05 -30.55 log R −5.01 0.08 HK 0.06 Prot. [days] 15. 0.04 0.02 M [M]1.33 0 -0.02 Teff [K] 6340 ± 39 O-C [km/s] -0.04 ± -0.06 log g [cgs] 4.46 0.02 -0.08 −1 v sin i [km s ]7.3 ± 1.5 50500 51000 51500 52000 52500 53000 53500 54000 age [Gyr] 2.0 ± 0.5 JD-2400000 [days] Photometric and spectral type are from Chauvin et al. (2006). Fig. 1. ELODIE and CORALIE radial velocities for HD 196885 A, Astrometric parameters are from HIPPARCOS (ESA 1997). The superimposed on a two-Keplerian orbital solution (Table 2). mass M and the atmospheric parameters Teff ,logg and [Fe/H] are from Sousa et al. (2006). The bolometric correction is computed from Flower HD 196885A ELODIE + CORALIE + CORAVEL ff (1996) using the spectroscopic Te determination. The activity level and 0.1 the rotation period are from Wright et al. (2004). The given age was ob- Ab tained following the Bayesian approach of Pont & Eyer (2004). 0.05 0 = − is very weak: log RHK 5.01 (Wright et al. 2004). From this value, these authors inferred a rotation period of about 15 days. -0.05 Radial velocity [km/s] According to Pace & Pasquini (2004), the activity level becomes ∼ -0.1 weak and constant after 1.5 Gyr, setting a lower limit on the age 2 ELODIE of the star. On the other hand, following the Bayesian approach B CORALIE 1 CORAVEL described in Pont & Eyer (2004) we estimate a maximum age of 2.5 Gy. The derived stellar atmospheric parameters and age 0 are compatible with the expected values for a high metallicity -1 late-F dwarf (F8 V), and are slightly at odds with the evolution- -2 Radial velocity [km/s] ary status given by the HIPPARCOS catalogue. -3 0 0.2 0.4 0.6 0.8 1 phase 3. Orbital solutions for the HD 196885 system Fig. 2. Phase-folded radial velocities measurements and best fit for the The ELODIE observations of HD 196885 A started in June 1997 planetary companion of HD 196885 A (top) and the its stellar compan- and the last data acquired are from August 2006, since the ion (bottom). For each body the contribution by the other companion ELODIE program was closed shortly after that date. The peculiar has been subtracted from the observational data. The orbital period of variations of the radial velocities (Fig. 1) and also non-confirmed the inner body is P = 3.7 yr, while for the outer body we have P = 55 yr announcements from other research teams (see Sect. 4), pre- (Table 2). However, the fact that we are unable to completely cover in vented us from announcing this system earlier. However, the re- phase the orbit of the stellar companion indicates that its orbital period may be considerably longer (Table 3). cent detection of a visual small stellar companion close to the main star (Chauvin et al. 2006, 2007) confirmed our suspicion of a long term drift of the radial velocities. Superimposed on the drift we can also observe a regular variation of a few years planetary companion, since the precision of CORALIE is slightly signaling the presence of a sub-stellar companion. better than the precision of ELODIE. Before the ELODIE program, the star HD 196885 A had been With 111 radial-velocity measurements (69 from followed between June 1982 and August 1997 by the CORAVEL ELODIE, 9 from CORAVEL and 33 from CORALIE), span- spectrometers (Baranne et al.
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