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The G0V star HD166435 has been observed by the fiber-fed spectrograph ELODIEas one of the targets in the large extra-solar planet survey that we areconducting at the Observatory of Haute-Provence. We detected coherent,low-amplitude, radial-velocity variations with a period of 3.7987days,suggesting a possible close-in planetary companion. Subsequently, we initiateda series of high-precision photometric observations to search for possibleplanetary transits and an additional series of CaII H and K observations tomeasure the level of surface magnetic activity and to look for possiblerotational modulation. Surprisingly, we found the star to be photometricallyvariable and magnetically active. A detailed study of the phase stability ofthe radial-velocity signal revealed that the radial-velocity variabilityremains coherent only for durations of about 30days. Analysis of the timevariation of the spectroscopic line profiles using line bisectors revealed acorrelation between radial velocity and line-bisector orientation. All of theseobservations, along with a one-quarter cycle phase shift between thephotometric and the radial-velocity variationss, are well explained by thepresence of dark photospheric spots on HD166435. We conclude that theradial-velocity variations are not due to gravitational interaction with anorbiting planet but, instead, originate from line-profile changes stemming fromstar spots on the surface of the star. The quasi-coherence of theradial-velocity signal over more than two years, which allowed a fair fit witha binary model, makes the stability of this star unusual among other activestars. It suggests a stable magnetic field orientation where spots are alwaysgenerated at about the same location on the surface of the star.Comment: 9 pages, 8 figures, Accepted for publication in A&

No planet for HD 166435