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The CORALIE survey for southern extra-solar planets IX. A 1.3-day period brown dwarf disguised as a planet

N. C. Santos·M. Mayor·D. Naef·F. Pepe·D. Queloz·S. Udry·M. Burnet·J. V. Clausen·B. E. Helt·E. H. Olsen·J. D. Pritchard
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Abstract

In this article we present the case of HD 41004 AB, a system composed of a K0V star and a 3.7-magnitude fainter M-dwarf companion separated by only 0.5 arcsec. An analysis of CORALIE radial-velocity measurements has revealed a variation with an amplitude of about 50m/s and a periodicity of 1.3days. This radial-velocity signal is consistent with the expected variation induced by the presence a very low mass giant planetary companion to HD 41004 A, whose light dominates the spectra. The radial-velocity measurements were then complemented with a photometric campaign and with the analysis of the bisector of the CORALIE Cross-Correlation Function (CCF). While the former revealed no significant variations within the observational precision of 0.003-0.004 mag (except for an observed flare event), the bisector analysis showed that the line profiles are varying in phase with the radial-velocity. This latter result, complemented with a series of simulations, has shown that we can explain the observations by considering that HD 41004 B has a brown-dwarf companion orbiting with the observed 1.3-day period. If confirmed, this detection represents the first discovery of a brown dwarf in a very short period (1.3-day) orbit around an M dwarf. Finally, this case should be taken as a serious warning about the importance of analyzing the bisector when looking for planets using radial-velocity techniques.

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N. C. Santos, M. Mayor, D. Naef, F. Pepe, D. Queloz, S. Udry, M. Burnet, J. V. Clausen, B. E. Helt, E. H. Olsen, J. D. Pritchard. 2002-06-13. The CORALIE survey for southern extra-solar planets IX. A 1.3-day period brown dwarf disguised as a planet. https://doi.org/10.1051/0004-6361%3A20020876

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