HST search for giant planets around white dwarfs in the Hyades

We carried out a deep high-contrast direct imaging search for giant planets around seven single white dwarfs in the nearby (average distance approximately 45 pc) Hyades open cluster (age 625 Myr) using the Hubble Space Telescope and its NICMOS instrument. No planets were found. Compared to a previous search with SPITZER/IRAC using infrared excess in the white dwarfs as an indicator for unresolved very low-mass companions, which derived detection limits of 7 to 11 M_Jup, our detection limits for angular separations ≥500mas are considerably lower, i.e. in the range 5 to 7 M_Jup. The non-detections are in line with radial velocity studies around K-type giants, which do not find any giant planets around stars more massive than 3 solar masses. This might indicate that initially dense cluster environments hinder the formation of massive giant planets, or that the energetic radiation of the host stars effects dust growth and gas evaporation, and hence the planet formation efficiency.