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

By Nuno C. Santos, M. Mayor, D. Naef, F. Pepe, D. Queloz, S. Udry, M. Burnet, J. Clausen, B. Helt, E. H. Olsen and 6 more. 2002

201 citations recorded by the source corpus.

In this article we present the case of HD 41004 AB, a system composed of a K0V star and a 3.7-mag fainter M-dwarf companion. We have obtained 86 CORALIE spectra of this system with the goal of obtaining precise radial-velocity measure- ments. Since HD 41004 A and B are separated by only 0.5 00 , in every spectrum taken for the radial-velocity measurement, we are observing the blended spectra of the two stars. An analysis of the measurements has revealed a velocity variation with an amplitude of about 50 m s 1 and a periodicity of 1.3 days. This radial-velocity signal is consistent with the expected variation induced by the presence of a companion to either HD 41004 A or HD 41004 B, or to some other eect due to e.g. activity related phenomena. In particular, such a small velocity amplitude could be the signature of the presence of a very low mass giant plane- tary 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 of0.003-0.004 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. As the spectrum of the fainter HD 41004 B "moves" relative to the one of HD 41004 A (with an amplitude of a few km s 1 ), the relative position of the spectral lines of the two spectra changes, thus changing the blended line-profiles. This variation is large enough to explain the observed radial-velocity and bisector variations, and is compatible with the absence of any photometric signal. 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.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

The Transiting Extrasolar Giant Planet around the Star OGLE-TR-113 (2004, methodology): “This was done directly from the cross-correlation function of OGLE-TR-113 co-added over all echelle orders, following Santos et al. (2002) and Torres et al. (2004).”
Two new “very hot Jupiters” among the OGLE transiting candidates (2004, unknown): “Furthermore the CCF was computed with different masks without significant change in the radial velocity values (as discussed by Santos et al. 2002, most blend scenarios produce mask-dependent velocities).”
The CORALIE survey for southern extra-solar planets. XII. Orbital solutions for 16 extra-solar planets discovered with CORALIE (2003, methodology): “From calibrations of the width and surface of the CORALIE crosscorrelation functions (CCF; described in Santos et al. 2002), we also derive the stellar projected rotational velocity v sin i and [Fe/H] when not available from the spectral analysis.”
The HARPS survey for southern extra-solar planets. II. A 14 Earth-masses exoplanet around μ Arae (2004, methodology): “From the width of the CORALIE Cross-Correlation Function (CCF) we have computed a projected rotational velocity of 2.4 km s−1 for µAra (Santos et al. 2002).”
THE KEPLER-10 PLANETARY SYSTEM REVISITED BY HARPS-N: A HOT ROCKY WORLD AND A SOLID NEPTUNE-MASS PLANET (2014, methodology): “Another way of estimating the v sin i is to look at the FWHM of the cross correlation function used to derive the RVs (Boisse et al. 2010; Santos et al. 2002).”
PASTIS: Bayesian extrasolar planet validation. I. General framework, models, and performance (2014, methodology): “…synthetic CCFs for each modelled star using the instrument-dependent empirical rela- tions between stellar parameters (z and B − V colour index) and CCF contrast and width obtained by Santos et al. (2002), Boisse et al. (2010), and additional relations described in Santerne et al. (in preparation).”
SOPHIE velocimetry of Kepler transit candidates XVII. The physical properties of giant exoplanets within 400 days of period (2015, unknown): “These spectroscopic diagnostics are used to reveal the presence of contaminating stars, therefore likely false positives that might be the source of the transit event (Santos et al. 2002; Torres et al. 2005).”
The HARPS search for Earth-like planets in the habitable zone - I. Very low-mass planets around HD 20794, HD 85512, and HD 192310 (2011, background): “The third part of Table 3 shows additional stellar parameters: the projected stellar rotation velocity is issued from the instrumental calibration presented by Santos et al. (2002).”
TW Hydrae: evidence of stellar spots instead of a Hot Jupiter (2008, background): “On the other hand, an amplitude dependence on the mask used could be expected if the RV signal is produced by the presence of a stellar blend (Santos et al. 2002) or a cool stellar spot.”
WASP-121 b: a hot Jupiter close to tidal disruption transiting an active F star (2015, background): “These variations do not phase with the transit ephemeris, as one might expect if the observed RV signal was originating from a false-positive scenario, such as a blended eclipsing binary (see e.g. Santos et al. 2002).”
Spectroscopic metallicities for planet-host stars: Extending the samples (2005, background): “The stellar parameters for HD 41004A may suffer from the fact that the spectrum of this star is blended with the spectrum of the fainter M-dwarf companion HD 41004 B (see e.g. Santos et al. 2002).”
ELODIE metallicity-biased search for transiting Hot Jupiters. II. A very hot Jupiter transiting the bright K star HD 189733 (2005, methodology): “In practice, the first spectroscopic measurement is made to estimate the metallicity by measuring the surface of the cross-correlation function ofthe ELODIE spectrum (Santos et al. 2002).”
Metallicity of M dwarfs - I. A photometric calibration and the impact on the mass-luminosity relation at the bottom of the main sequence (2005, methodology): “This sample of single F, G or K dwarfs is representative of the solar neighbourhood, and we estimate their metallicity using the Santos et al. (2002) calibration of the area of the cross-correlation function between the stellar spectra and an appropriate template.”
Stellar activity of planetary host star HD 189 733 (2008, background): “The precision of radial-velocity (RV) searches for exoplanets depends on the noise induced by photospheric luminosity variations due to active regions (e.g. Santos et al. 2002).”