A near-infrared interferometric survey of debris-disk stars. VII. The hot/warm dust connection

Context. Hot exozodiacal dust has been shown to be present in the innermost regions of an increasing number of main sequence stars over the past fifteen years. The origin of hot exozodiacal dust and its connection with outer dust reservoirs remains however unclear. Aims. We aim to explore the possible connection between hot exozodiacal dust and warm dust reservoirs (≥ 100 K) in asteroid belts. Methods. We use precision near-infrared interferometry with VLTI/PIONIER to search for resolved emission at H band around a selected sample of 62 nearby stars showing possible signposts of warm dust populations.
Results. Our observations reveal the presence of resolved near-infrared emission around 17 out of 52 stars with sufficient data quality, four of which are shown to be due to a previously unknown stellar companion. The 13 other H-band excesses are thought to originate from the thermal emission of hot dust grains, close to their sublimation temperature. Taking into account earlier PIONIER observations, where some stars with warm dust were also observed, and after re-evaluating the warm dust content of all our PIONIER targets through spectral energy distribution modeling, we find a detection rate of 17.1(+8.1)(-4.6)% for H-band excess around main sequence stars hosting warm dust belts, which is statistically compatible with the occurrence rate of 14.6(+4.3)(-2.8)% found around stars showing no signs of warm dust. After correcting for the sensitivity loss due to partly unresolved hot disks, under the assumption that they are arranged in a thin ring around their sublimation radius, we however find tentative evidence at the 3σ level that H-band excesses around stars with outer dust reservoirs (warm or cold) could be statistically larger than H-band excesses around stars with no detectable outer dust.
Conclusions. Our observations do not suggest a direct connection between warm and hot dust populations, at the sensitivity level of the considered instruments, although they bring to light a possible correlation between the level of H-band excesses and the presence of outer dust reservoirs in general.