The HOSTS survey - Exozodiacal dust measurements for 30 stars

TL;DR

The HOSTS survey used nulling interferometry to measure exozodiacal dust levels around 30 nearby stars, finding an 18% detection rate and setting upper limits on dust levels to inform future exo-Earth imaging efforts.

Contribution

This study provides the first detections of exozodiacal dust around Sun-like stars and refines occurrence rates, demonstrating improved sensitivity and the importance of target vetting for future missions.

Findings

Detection rate of 18%, including first detections around Sun-like stars.

Upper limits on median dust levels are 13 to 26 zodis.

Sensitivity improved by a factor of 5-10 over previous results.

Abstract

The HOSTS (Hunt for Observable Signatures of Terrestrial Systems) survey searches for dust near the habitable zones (HZs) around nearby, bright main sequence stars. We use nulling interferometry in N band to suppress the bright stellar light and to probe for low levels of HZ dust around the 30 stars observed so far. Our overall detection rate is 18%, including four new detections, among which are the first three around Sun-like stars and the first two around stars without any previously known circumstellar dust. The inferred occurrence rates are comparable for early type and Sun-like stars, but decrease from 60 (+16/-21)% for stars with previously detected cold dust to 8 (+10/-3)% for stars without such excess, confirming earlier results at higher sensitivity. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal excess luminosity function, we put upper limits on the median HZ dust level of 13 zodis (95% confidence) for a sample of stars without cold dust and of 26 zodis when focussing on Sun-like stars without cold dust. However, our data suggest that a more complex luminosity function may be more appropriate. For stars without detectable LBTI excess, our upper limits are almost reduced by a factor of two, demonstrating the strength of LBTI target vetting for future exo-Earth imaging missions. Our statistics are so far limited and extending the survey is critical to inform the design of future exo-Earth imaging surveys.