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GIARPS KILLS A HOT-JUPITER

Thanks to simultaneous observations in the visible and near infrared through HARPS-N and GIANO-B at TNG, it was possible to better understand the Radial Velocity (RV) variations observed in the young active star BD+201790.

The high level of stellar activity characterizing young stars induces RV variations able to mimic planetary signals, thus simultaneous multi-band high-resolution spectroscopy is a powerful tool for disentangling the mechanism at work. Orbital RVs are achromatic, so the amplitude does not change at different wavelengths, while stellar activity induces wavelength-dependent radial velocity variations, which are significantly reduced in the near infrared range with respect to the visible.

This task can be accomplished by observing in a configuration called GIARPS, in which the light is splitted to reach both GIANO-B and HARPS-N spectrographs, thus acquiring spectra simultaneously in the near infrared and visible wavelength spectrum, respectively.

In the particular case of BD+201790, there is a significant difference between the RV amplitude measured in the visual and the near infrared. Further analysis, exploiting light curves from photometric observations, lead to consider a mixture of cool and hot spots in the same active region to be responsible of the observed behaviour.

These results ruled out the presence of the previously announced hot-Jupiter planet around BD+201790.

Orbital fit at 7.78 days found by Hernán-Obispo et al. 2015 compared to phase-folded visible and near infrared RVs. Top panel: Orbital fit (black dashed line) obtained with the visible data (FOCES, SARG, and HERMES Radial Velocities from Hernán-Obispo et al. 2015, grey dots) and HARPS-N 2015 RVs (green dots). Bottom panel: Orbital fit (black dashed line), GIANO/GIANO-B (red dots), IGRINS (light blue dots), and HARPS-N 2017 (black asterisks, two acquired in GIARPS mode) RVs.

The figure shows that the amplitude of near infrared RVs (calculated as the difference between maximum and minimum RVs) is 437.3 m/s, four times lower with respect to the optical one reported in Hernán-Obispo et al. 2015 and interpreted as a signature of a hot Jupiter. Therefore, according to GIARPS data, the team can exclude any companion with those characteristics, ascribing the observed variation to phenomena of stellar origin.

As in the case of HARPS-N (http://www.tng.iac.es/news/2013/04/08/gaps/), the first result of the new instrument is the invalidation of a previously announced exoplanet !

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