The Hosts Survey: Evidence For An Extended Dust Disk And Constraints On The Presence Of Giant Planets In The Habitable Zone Of Beta Leo

The young (50-400 Myr) A3V star beta Leo is a primary target to study the formation history and evolution of extrasolar planetary systems as one of the few stars with known hot (similar to 1600 K), warm (similar to 600 K), and cold (similar to 120 K) dust belt components. In this paper, we present deep mid-infrared measurements of the warm dust brightness obtained with the Large Binocular Telescope Interferometer (LBTI) as part of its exozodiacal dust survey (HOSTS). The measured excess is 0.47% 0.050% within the central 1.5 au, rising to 0.81% 0.026% within 4.5 au, outside the habitable zone of beta Leo. This dust level is 50 10 times greater than in the solar system's zodiacal cloud. Poynting-Robertson drag on the cold dust detected by Spitzer, and Herschel underpredicts the dust present in the habitable zone of beta Leo, suggesting an additional delivery mechanism (e.g., comets) or an additional belt at similar to 5.5 au. A model of these dust components is provided that implies the absence of planets more than a few Saturn masses between similar to 5 au and the outer belt at similar to 40 au. We also observationally constrain giant planets with the LBTI imaging channel at 3.8 mu m wavelength. Assuming an age of 50 Myr, any planet in the system between approximately 5-50 au must be less than a few Jupiter masses, consistent with our dust model. Taken together, these observations showcase the deep contrasts and detection capabilities attainable by the LBTI for both warm exozodiacal dust and giant exoplanets in or near the habitable zone of nearby stars.