EDP Sciences
Free access
Volume 379, Number 1, November III 2001
Page(s) 279 - 287
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011308

A&A 379, 279-287 (2001)
DOI: 10.1051/0004-6361:20011308

No planet for HD 166435

D. Queloz1, G. W. Henry2, J. P. Sivan3, S. L. Baliunas2, 4, 5, J. L. Beuzit6, R. A. Donahue4, 5, M. Mayor1, D. Naef1, C. Perrier6 and S. Udry1

1  Observatoire de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
    e-mail: Didier.Queloz@obs.unige.ch
2  Center of Excellence in Information Systems, Tennessee State University, 330 10th Avenue North, Nashville, TN 37203, USA
3  Observatoire de Haute Provence, 04870 Saint-Michel l'Observatoire, France
4  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
5  Mount Wilson Observatory, 740 Holladay Road, Pasadena, CA 91106, USA
6  Observatoire de Grenoble, 414 rue de la Piscine, 38041 Domaine Universitaire de St Martin d'Hères, France

(Received 9 August 2001 / Accepted 20 September 2001)

The G0 V star HD 166435 has been observed by the fiber-fed spectrograph ELODIE as one of the targets in the large extra-solar planet survey that we are conducting at the Observatory of Haute-Provence. We detected coherent, low-amplitude, radial-velocity variations with a period of 3.7987 days, suggesting a possible close-in planetary companion. Subsequently, we initiated a series of high-precision photometric observations to search for possible planetary transits and an additional series of Ca II H and K observations to measure the level of surface magnetic activity and to look for possible rotational modulation. Surprisingly, we found the star to be photometrically variable and magnetically active. A detailed study of the phase stability of the radial-velocity signal revealed that the radial-velocity variability remains coherent only for durations of about 30 days. Analysis of the time variation of the spectroscopic line profiles using line bisectors revealed a correlation between radial velocity and line-bisector orientation. All of these observations, along with a one-quarter cycle phase shift between the photometric and the radial-velocity variations, are well explained by the presence of dark photospheric spots on HD 166435. We conclude that the radial-velocity variations are not due to gravitational interaction with an orbiting planet but, instead, originate from line-profile changes stemming from star spots on the surface of the star. The quasi-coherence of the radial-velocity signal over more than two years, which allowed a fair fit with a binary model, makes the stability of this star unusual among other active stars. It suggests a stable magnetic field orientation where spots are always generated at about the same location on the surface of the star.

Key words: stars: activity -- individual: HD 166435 -- planetary systems

Offprint request: D. Queloz, queloz@obs.unige.ch

SIMBAD Objects

© ESO 2001