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The ELODIE Survey for Northern Extra-Solar Planets IV. HD196885, A

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The ELODIE Survey for Northern Extra-Solar Planets IV. HD196885, A Astronomy & Astrophysics manuscript no. hd196885 c ESO 2018 December 2, 2018 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. S´egransan5 1 Departamento de F´ısica da Universidade de Aveiro, Campus Universit´ario de Santiago, 3810-193 Aveiro, Portugal 2 Observatoire de Gen`eve, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland 3 Laboratoire d’Astrophysique de Grenoble, Universit´eJoseph 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 Astrof´ısica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal Received 01 October, 2006; accepted ?? ABSTRACT Aims. We aim significantly increase the number of detected extra-solar planets in a magnitude-limited sample to improve our knowl- edge of their orbital elements 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 ties with the two detected companionsare described in Sect. 3.In Sect. 4 we discuss the possibility of the existence of more com- The ELODIE Planet Search Survey was an extensive radial- panions, in particular with orbital periods around 368 days. Last velocity northern survey of dwarf stars at the Haute-Provence section is devoted to our conclusions. Observatory (OHP, France) using the ELODIE high-precision fiber-fed echelle spectrograph (Baranne et al. 1996) mounted at the Cassegrain focus of the 1.93-mtelescope.It started to operate 2. HD 196885 A stellar characteristics at the end of 1993 and acquired data until the summer of 2006, when it was replaced by the new echelle spectrograph SOPHIE HD 196885A was observed by the HIPPARCOS astrometric (Bouchy & The Sophie Team 2006). satellite (HIP 101966). A high-precision spectroscopic study of This survey is part of a large effort aimed at an extra-solar this star was also performed by Sousa et al. (2006) in order to planet search through radial-velocity measurements, in order to examine the metallicity distribution of stars hosting planets. This characterize the types of exoplanets and to bring strong con- star was also studied by near-infrared survey with adaptive op- straints on their processes of formation and evolution. ELODIE tics of faint circumstellar environments, sensitive to compan- was responsible for finding many extra-solar planets, among ions within the stellar and the sub-stellar domains (Chauvin et al. them the first hot Jupiter, 51Pegb (Mayor & Queloz 1995). The 2006, 2007). Observed and inferred stellar parameters from arXiv:0711.3343v2 [astro-ph] 22 Dec 2016 original sample consisted of 142 stars, but a new sample of 330 these different sources are summarized in Table1. stars was defined in 1997. Details of the program and the sur- In the HIPPARCOS catalogue, HD 196885A is given a spec- veyed sample can be found in Perrier et al. (2003). tral type F8 IV, a visual magnitude V = 6.398 and a color in- In this paper we present the detection of two bodies around dex B − V = 0.559. The measured parallax (30.31 ± 0.81 mas) the star HD 196885A, one in the mass range of planets and the leads to a distance of 33.0 ± 0.9 pc and an absolute magnitude other believed to be a stellar companion.This star was previously of MV = 3.8 ± 0.1. From CORALIE spectra, Sousa et al. (2006) described to harbor a planet with a period of about 386 days (al- derived an effective temperature Teff = 6340±39K, a gravitylog though no published reference is known), but we could not con- g = 4.46 ± 0.02 and a high metal content [Fe/H] = 0.29 ± 0.05 firm its presence in our observations(our analysis shows a planet (Table1). The bolometric correction (BC = −0.006)is computed with an orbital period of about 1349 days instead). The stellar from Flower (1996) using the spectroscopic Teff determination. companion was also recently observed using NACO adaptative The bolometric magnitudeis then MBol = 3.791, which allows us optics by Chauvin et al. (2006, 2007). The stellar properties of to derive a stellar luminosity of L = 2.40 L⊙. Sousa et al. (2006) HD 196885A are briefly recalled in Sect.2 and the radial veloci- also computed the mass, M = 1.33 M⊙, from evolutionary tracks using Genevamodels(Schaller et al. 1992; Schaerer et al. 1993). Send offprint requests to: A.C.M. Correia, e-mail: [email protected] From the B − V value and ELODIE correlation functions we 2 A.C.M. Correia et al.: HD 196885, a close binary star with a 3.7-year planet Table 1. Observed and inferred stellar parameters for HD 196885A ELODIE + CORALIE -30.1 HD 196885A. ELODIE -30.15 CORALIE -30.2 Parameter HD 196885 A -30.25 Spectral Type F8 V -30.3 V 6.398 -30.35 B − V 0.559 ± 0.006 π [mas] 30.31 ± 0.81 -30.4 d [pc] 33.0 ± 0.9 Radial velocity [km/s] -30.45 M 3.8 ± 0.1 V -30.5 BC −0.006 -30.55 MBol 3.79 L [L⊙] 2.40 0.08 0.06 [Fe/H] 0.29 ± 0.05 0.04 ′ 0.02 log RHK −5.01 0 -0.02 Prot. [days] 15. O-C [km/s] -0.04 M [M⊙] 1.33 -0.06 ± -0.08 Teff [K] 6340 39 50500 51000 51500 52000 52500 53000 53500 54000 log g [cgs] 4.46 ± 0.02 JD-2400000 [days] v sin i [km/s] 7.3 ± 1.5 age [Gyr] 2.0 ± 0.5 Fig. 1. ELODIE and CORALIE radial velocities for HD 196885A, superimposed on a two-Keplerian orbital solution (Table 2). Photometric and spectral type are from Chauvin et al. (2006). Astrometric parameters are from HIPPARCOS (ESA 1997). The mass M and the atmospheric parameters Teff, log g and [Fe/H] are from Sousa et al. (2006). The bolometric correction is computed from Flower a series of radial velocity measurements were also taken using (1996) using the spectroscopic Teff determination. The activity level and the CORALIE echelle spectrograph(Queloz et al. 2000) mounted the rotation period are from Wright et al. (2004). The given age was ob- on the 1.2-m Swiss telescope at La Silla. This four year obser- tained following the Bayesian approach of Pont & Eyer (2004). vational sequence is important to confirm the presence of the planetary companion, since the precision of CORALIE is slightly find v sin i = 7.3 ± 1.5 [km/s], meaning that the star is ro- better than the precision of ELODIE. tating fast. However, its measured activity level is very weak: With 111 radial-velocity measurements (69 from ELODIE,9 ′ from CORAVEL and 33 from CORALIE), spanning ∼14 years of log RHK = −5.01 (Wright et al. 2004). From this value, these authors inferred a rotation period of about 15 days. According observations, we are able to describe the orbit of the sub-stellar to Pace & Pasquini (2004), the activity level becomes weak and body in the system, as well as slightly constrain the orbit of constant after ∼1.5 Gyr, setting a lower limit on the age of the the stellar companion. Using the iterative Levenberg-Marquardt star. On the other hand, following the Bayesian approach de- method (Press et al. 1992), we first attempt to fit the complete scribed in Pont & Eyer (2004) we estimate a maximum age of set of radial velocities with a single orbiting companion and 2.5 Gy. The derived stellar atmospheric parameters and age are a quadratic drift. This fit yields a planetary companion with compatible with the expected values for a high metallicity late- P = 1347days, e = 0.44, a minimum mass of 2.9 MJup and F dwarf (F8 V), and are slightly at odds with the evolutionary an adjustment of pχ2 = 1.811 and rms = 14.61m/s. We then status given by the HIPPARCOS catalogue. fit the radial velocities using a model with two Keplerian orbits (Figs.1 and 2). It yields for the inner planet P = 1349 days, e = 0.46 and a minimum mass of 3.0 MJup, while for the outer 3. Orbital solutions for the HD 196885 system companion we have P ≃ 20000 days, e = 0.41 and a minimum The ELODIE observations of HD 196885A started in June 1997 mass of 0.34 M⊙ (Table 2). Despite all the uncertainties in the and the last data acquired are from August 2006, since the orbital parameters, the use of a Keplerian orbit for the massive ELODIE program was closed shortly after that date. The peculiar outer body in the system proved to be a good approach, better variations of the radial velocities (Fig.1) and also non-confirmed than the quadratic drift, since the reduced pχ2 is now 1.494 and announcements from other research teams (see section 4), pre- the velocity residuals drop to rms = 11.87m/s (Fig.2).
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