The HARPS search for southern extra-solar planets.
XXXV. The interesting case of HD41248: stellar activity, no planets?

N. C. Santos, A. Mortier, J. P. Faria, X. Dumusque, V. Zh. Adibekyan, E. Delgado Mena, P. Figueira, L. Benamati, I. Boisse, D. Cunha, J. Gomes da Silva, G. Lo Curto, C. Lovis, J. H. C. Martins, M. Mayor, C. Melo, M. Oshagh, F. Pepe, D. Queloz, A. Santerne, D. Ségransan, A. Sozzetti, S. G. Sousa, S. Udry

Abstract
Context. The search for planets orbiting metal-poor stars is of uttermost importance for our understanding of the planet formation models. However, no dedicated searches have been conducted so far for very low mass planets orbiting such objects. Only a few cases of low mass planets orbiting metal-poor stars are thus known. Amongst these, HD41248 is a metal-poor, solar-type star on which a resonant pair of super-Earth like planets has been announced. This detection was based on 62 radial velocity measurements obtained with the HARPS spectrograph (public data).
Aims. In the present paper we present a new planet search program that is using the HARPS spectrograph to search for Neptunes and Super-Earths orbiting a sample of metal-poor FGK dwarfs. We then present a detailed analysis of an additional 162 radial velocity measurements of HD41248, obtained within this program, with the goal of confirming the existence of the proposed planetary system.
Methods. We analyzed the precise radial velocities, obtained with the HARPS spectrograph, together with several stellar activity diagnostics and line profile indicators.
Results. A careful analysis shows no evidence for the planetary system previously announced. One of the signals, with a period of ∼25 days, is shown to be related to the rotational period of the star, and is clearly seen in some of the activity proxies. The remaining signal (P∼18 days) could not be convincingly retrieved in the new data set.
Conclusions. We discuss possible causes for the complex (evolving) signals observed in the data of HD41248, proposing that they may be explained by the appearance and disappearance of active regions on the surface of a star with strong differential rotation, or by a combination of the sparse data sampling and active region evolution.

Keywords
planetary systems – stars: individual: HD 41248 – stars: solar-type – stars: activity – stars: abundances – surveys

Notes
Based on observations collected at ESO facilities under programs 082.C-0212, 085.C-0063, 086.C-0284, and 190.C-0027 (with the HARPS spectrograph at the ESO 3.6-m telescope, La Silla-Paranal Observatory).

Astronomy and Astrophysics
Volume 566, Page A35_1
June 2014

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