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Description
Young stars with debris disks are the most promising targets for an exoplanet search because debris indicate a successful formation of planetary bodies. Debris disks can be shaped by planets into ring structures that give valuable indications on the presence and location of planets in the disk. We performed observations of the Sco-Cen F star HD 117214 to search for planetary companions and to characterize the debris disk structure. HD 117214 was observed with the SPHERE subsystems IRDIS, IFS, and ZIMPOL at optical and near-IR wavelengths using angular and polarimetric differential imaging techniques. This provided the first images of scattered light from the debris disk with the highest spatial resolution of 25mas and an inner working angle <0.1". With the observations with IRDIS and IFS we derived detection limits for substellar companions. The geometrical parameters of the detected disk were constrained by fitting 3D models for the scattering of an optically thin dust disk. Investigating the possible origin of the disk gap, we introduced putative planets therein and modeled the planet-disk and planet-planet dynamical interactions. The obtained planetary architectures were compared with the detection limit curves. The debris disk has an axisymmetric ring structure with a radius of 0.42(+/-0.01)" or ~45au and an inclination of 71(+/-2.5){deg} and exhibits a 0.4" (~40au) wide inner cavity. From the polarimetric data, we derive a polarized flux contrast for the disk of (Fpol)_disk_/F*=(3.1+/-1.2)x10^-4^ in the RI band. The fractional scattered polarized flux of the disk is eight times lower than the fractional IR flux excess. This ratio is similar to the one obtained for the debris disk HIP 79977, indicating that dust radiation properties are similar for these two disks. Inside the disk cavity we achieve high-sensitivity limits on planetary companions with a mass down to ~4M_J_ at projected radial separations between 0.2" and 0.4". We can exclude stellar companions at a radial separation larger than 75mas from the star.
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