The HOSTS Survey: Direct Measurement of Exozodiacal Dust Levels in the Habitable Zones of Nearby Stars
Friday 6 July, 12:50
The presence of large amounts of circumstellar dust in Habitable Zones of nearby stars could pose a significant challenge to future space missions designed to directly image and spectrally characterize Earth-like exoplanets. The HOSTS survey is designed to measure levels of exozodiacal dust in the HZs of bright, nearby main sequence stars. We use the Large Binocular Telescope Interferometer (LBTI) to null out direct starlight and detect faint, extended dust emission in the thermal infrared at 10 microns. We present the first results from our survey of > 30 stars observed so far. The results provide new insight into the incidence rate, typical levels, and origin of HZ dust. Excess emission is found in four new sources and confirmed in three others. The new detections include the first around Sun-like stars and the first around stars without previously known circumstellar dust. The overall detection rate is 18 (+9/-5)% and is strongly correlated the presence of cool outer dust belts detected with Spitzer and Herschel. Assuming a log-normal excess luminosity function, the upper limits on the median HZ dust level is 13 zodis (95% confidence) for all stars without cold dust, and 26 zodis for Sun-like stars without cold dust. These limits are 5-10 times better than previous results from the Keck interferometer. They are consistent with a bimodal distribution where some stars have high HZ dust levels but the majority have dust levels below our sensitivity. Preliminary implications of these results for future exo-Earth direct imaging missions will be discussed.