A near-infrared interferometric survey of debris disc stars. III. First statistics based on 42 stars observed with CHARA/FLUOR

摘要

(Abridged) Dust is expected to be ubiquitous in extrasolar planetary systemsowing to the dynamical activity of minor bodies. Inner dust populations are,however, still poorly known because of the high contrast and small angularseparation with respect to their host star. We aim to determine the level ofnear-infrared exozodiacal dust emission around a sample of 42 nearby mainsequence stars with spectral types ranging from A to K and to investigate itscorrelation with various stellar parameters and with the presence of cold dustbelts. We use high-precision K-band visibilities obtained with the FLUORinterferometer on the shortest baseline of the CHARA array. The calibratedvisibilities are compared with the expected visibility of the stellarphotosphere to assess whether there is an additional, fully resolvedcircumstellar emission. Near-infrared circumstellar emission amounting to about1% of the stellar flux is detected around 13 of our 42 target stars. Follow-upobservations showed that one of them (eps Cep) is associated with a stellarcompanion, while another one was detected around what turned out to be a giantstar (kap CrB). The remaining 11 excesses found around single main sequencestars are most probably associated with hot circumstellar dust, yielding anoverall occurrence rate of 28+8-6% for our (biased) sample. We show that theoccurrence rate of bright exozodiacal discs correlates with spectral type,K-band excesses being more frequent around A-type stars. It also correlateswith the presence of detectable far-infrared excess emission in the case ofsolar-type stars. This study provides new insight into the phenomenon of brightexozodiacal discs, showing that hot dust populations are probably linked toouter dust reservoirs in the case of solar-type stars. For A-type stars, noclear conclusion can be made regarding the origin of the detected near-infraredexcesses.