A.M. and the GAPS project team acknowledge support from the "Progetti Premiali" funding scheme of the Italian Ministry of Education, University, and Research. I.P. acknowledges support from the European Union Seventh Framework Programme FP7/2007–2013, under the grant agreement No. 267251 "Astronomy Fellowships in Italy" (AstroFIt). ; The large number of close-in Jupiter-size exoplanets prompts the question whether star-planet interaction (SPI) effects can be detected. We focused our attention on the system HD 17156, having a Jupiter-mass planet in a very eccentric orbit. Here we present results of the XMM-Newton observations and of a five month coordinated optical campaign with the HARPS-N spectrograph. We observed HD 17156 with XMM-Newton when the planet was approaching the apoastron and then at the following periastron passage, quasi-simultaneously with HARPS-N. We obtained a clear (≈ 5.5σ ) X-ray detection only at the periastron visit, accompanied by a significant increase of the R'_HK chromospheric index. We discuss two possible scenarios for the activity enhancement: magnetic reconnection and flaring or accretion onto the star of material tidally stripped from the planet. In any case, this is possibly the first evidence of a magnetic SPI effect caught in action.
Our nearest neighbor, Proxima Centauri, hosts a temperate terrestrial planet. We detected in radial velocities evidence of a possible second planet with minimum mass mc sin ic = 5.8 ± 1.9M⊕ and orbital period P c = 5.21 −0.22 +0.26 years. The analysis of photometric data and spectro-scopic activity diagnostics does not explain the signal in terms of a stellar activity cycle, but follow-up is required in the coming years for confirming its planetary origin. We show that the existence of the planet can be ascertained, and its true mass can be determined with high accuracy, by combining Gaia astrometry and radial velocities. Proxima c could become a prime target for follow-up and characterization with next-generation direct imaging instrumentation due to the large maximum angular separation of ~1 arc second from the parent star. The candidate planet represents a challenge for the models of super-Earth formation and evolution. ; Progetto Premiale 2015 FRONTIERA funding scheme of the Italian Ministry of Education, University, and Research Italian Space Agency INAF Italian Space Agency Science & Technology Facilities Council (STFC) Comisión Nacional de Investigación Científica y Tecnológica (CONICYT) CONICYT FONDECYT CONICYT project Basal Spanish MINECO State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award Science & Technology Facilities Council (STFC) European Union (EU)
