A multi-technique detection of an eccentric giant planet around the accelerating star HD 57625

Context. The synergy between different detection methods is a key asset in exoplanetology that allows the precise characterization of detected exoplanets and robust constraints even in the case of a non-detection. The interplay between imaging, radial velocities and astrometry has recently produced significant advancements in exoplanetary science.Aims. We report a first result of an ongoing survey performed with SHARK-NIR, the new high-contrast near-infrared imaging camera at the Large Binocular Telescope, in parallel with LBTI/LMIRCam in order to detect planetary companions around stars with a significant proper motion anomaly. We focus on HD 57625, a F8 star for which we determine a 4.8_{−2.9^{+3.7 Ga age, exhibiting significant astrometric acceleration and for which archival radial velocities indicate a previously undetected massive long-period companion.Methods. We analysed the imaging data we collected with SHARK-NIR and LMIRCam in synergy with the available public SOPHIE radial velocity time series and HIPPARCOS-Gaia proper motion anomaly. With this joint multi-technique analysis, we characterised the companion causing the astrometric and radial velocity signals.Results. The imaging observations result in a non-detection, indicating the companion to be in the substellar regime. This is confirmed by the synergic analysis of archival radial velocity and astrometric measurements resulting in the detection of HD 57625 b, a 8.43−0.91+1.1 MJup planetary companion with an orbital separation of 5.70−0.13+0.14 au and an eccentricity of 0.52−0.03+0.04.Conclusions. HD 57625 b joins the small but growing population of giant planets on outer orbits with a true mass determination provided by the synergic usage of multiple detection methods. This again proves the importance of a multi-technique analysis in providing a robust characterization of planetary companions.}}