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Register a new userEvidence against the young hot-Jupiter around BD +20 1790
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P. Figueira
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Context. The young active star BD +20 1790 is believed to host a substellar companion, revealed by radial-velocity measurements that detected the reflex motion induced on the parent star. Aims. A complete characterisation of the radial-velocity signal is necessary in order to assess its nature. Methods. We used CORALIE spectrograph to obtain precise (~10 m/s) velocity measurements on this active star, while characterizing the bisector span variations. Particular attention was given to correctly sample both the proposed planetary orbital period, of 7.8 days, and the stellar rotation period, of 2.4 days. Results. A smaller radial-velocity signal (with peak-to-peak variations <500 m/s) than had been reported previously was detected, with different amplitude on two different campaigns. A periodicity similar to the rotational period is found on the data, as well as a clear correlation between radial-velocities and bisector span. This evidence points towards a stellar origin of the radial-velocity variations of the star instead of a barycentric movement of the star, and repudiates the reported detection of a hot-Jupiter.
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BD+20 1790 is a young active, metal-rich, late-type K5Ve star. We have undertaken a study of stellar activity and kinematics for this star over the past few years. Previous results show a high level of stellar activity, with the presence of prominence-like structures, spots on the surface and strong flare events, despite the moderate rotational velocity of the star. In addition, radial velocity variations with a semi-amplitude of up to 1 km/s were detected. We investigated the nature of these radial velocity variations, in order to determine whether they are due to stellar activity or the reflex motion of the star induced by a companion. We have analysed high-resolution echelle spectra and also two-band photometry was obtained to produce the light curve and determine the photometric period. Based upon the analysis of the bisector velocity span, as well as spectroscopic indices of chromospheric indicators and taking into account the photometric analysis, we report that the best explanation for the RV variation is the presence of a sub-stellar companion. The Keplerian fit of the RV data yields a solution for a close-in massive planet with an orbital period of 7.78 days. The presence of the close-in massive planet could also be an interpretation for the high level of stellar activity detected. Since the RV data are not part of a planet search program, we can consider our results as a serendipitous evidence of a planetary companion. To date, this is the youngest main sequence star for which a planetary candidate has been reported.
This paper presents the simultaneous Bayesian analysis of the radial velocity and activity indices for the K5Ve active star BD+20 1790, that was proposed to host a close-in massive planet by Hernan-Obispo et al. (2010). The Bayesian analysis supports the hypothesis of a planetary companion. We present a new orbital solution after removing the two main contributions to the stellar jitter, one that varies with the photometric period and another that varies with the synodic period of the star+planet system. We use a new method to determine these jitter components, considering them as a second and third signals in the system. A discussion on possible magnetic star-planet-interaction is included, based on the Bayesian analysis of the activity indices. We propose two possible sources for flare events of this star: one related to the geometry of the system and the relative movement of the star+planet, and a second one purely stochastic source that is related to the evolution of stellar active regions. Also, we observe for the first time the magnetic field of the star, from spectropolarimetric data.
Context. Stellar activity is currently challenging the detection of young planets via the radial velocity (RV) technique. Aims. We attempt to definitively discriminate the nature of the RV variations for the young active K5 star BD+20 1790, for which visible (VIS) RV measurements show divergent results on the existence of a substellar companion. Methods. We compare VIS data with high precision RVs in the near infrared (NIR) range by using the GIANO - B and IGRINS spectrographs. In addition, we present for the first time simultaneous VIS-NIR observations obtained with GIARPS (GIANO - B and HARPS - N) at Telescopio Nazionale Galileo (TNG). Orbital RVs are achromatic, so the RV amplitude does not change at different wavelengths, while stellar activity induces wavelength-dependent RV variations, which are significantly reduced in the NIR range with respect to the VIS. Results. The NIR radial velocity measurements from GIANO - B and IGRINS show an average amplitude of about one quarter with respect to previously published VIS data, as expected when the RV jitter is due to stellar activity. Coeval multi-band photometry surprisingly shows larger amplitudes in the NIR range, explainable with a mixture of cool and hot spots in the same active region. Conclusions. In this work, the claimed massive planet around BD+20 1790 is ruled out by our data. We exploited the crucial role of multi- wavelength spectroscopy when observing young active stars: thanks to facilities like GIARPS that provide simultaneous observations, this method can reach its maximum potential.
We search for signatures of a distant planet around the two-million-year-old classical T-Tauri star CI Tau hosting a hot Jupiter candidate (M_{p} sin{i} ~ 8.1 M_{Jupiter}) in an eccentric orbit (e ~0.3). To probe the existence of an outer perturber, we reanalyzed 1.3 mm dust continuum observations of the protoplanetary disk around CI Tau obtained by the Atacama Large Millimeter/submillimeter Array. We found a gap structure at ~0.8 in CI Taus disk. Our visibility fitting assuming an axisymmetric surface brightness profile suggested that the gap is located at a deprojected radius of 104.5+/-1.6 au and has a width of 36.9+/-2.9 au. The brightness temperature around the gap was calculated to be ~2.3 K lower than that of the ambient disk. Gap-opening mechanisms such as secular gravitational instability and dust trapping can explain the gap morphology in the CI Tau disk. The scenario that an unseen planet created the observed gap structure cannot be ruled out, although the coexistence of an eccentric hot Jupiter and a distant planet around the young CI Tau would be challenging for gravitational scattering scenarios. The mass of the planet was estimated to be between ~0.25 M_{Jupiter} and ~0.8 M_{Jupiter} from the gap width and depth (0.41 +0.04/-0.06) in the modeled surface brightness image, which is lower than the current detection limits of high-contrast direct imaging. The young classical T-Tauri CI Tau may be a unique system to explore the existence of a potential distant planet as well as the origin of an eccentric hot Jupiter.
We report the discovery of an additional substellar companion in the CoRoT-20 system based on six years of HARPS and SOPHIE radial velocity follow-up. CoRoT-20 c has a minimum mass of 17 $pm$ 1 $M_{Jup}$ and it orbits the host star in 4.59$pm 0.05$ years, with an orbital eccentricity of 0.60 $pm$ 0.03. This is the first identified system with an eccentric hot Jupiter and an eccentric massive companion. The discovery of the latter might be an indication of the migration mechanism of the hot Jupiter, via Lidov-Kozai effect. We explore the parameter space to determine which configurations would trigger this type of interactions.
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