The HOSTS Survey for Exozodiacal Dust: Observational Results from the Complete Survey

Abstract

The Large Binocular Telescope Interferometer (LBTI) enables nulling interferometric observations across the N band (8 to 13 µm) to suppress a star's bright light and probe for faint circumstellar emission. We present and statistically analyze the results from the LBTI/HOSTS (Hunt for Observable Signatures of Terrestrial Systems) survey for exozodiacal dust. By comparing our measurements to model predictions based on the Solar zodiacal dust in the N band, we estimate a 1 σ median sensitivity of 23 zodis for early type stars and 48 zodis for Sun-like stars, where 1 zodi is the surface density of habitable zone (HZ) dust in the Solar system. Of the 38 stars observed, 10 show significant excess. A clear correlation of our detections with the presence of cold dust in the systems was found, but none with the stellar spectral type or age. The majority of Sun-like stars have relatively low HZ dust levels (best-fit median: 3 zodis, 1 σ upper limit: 9 zodis, 95% confidence: 27 zodis based on our N band measurements), while ∼20% are significantly more dusty. The Solar system's HZ dust content is consistent with being typical. Our median HZ dust level would not be a major limitation to the direct imaging search for Earth-like exoplanets, but more precise constraints are still required, in particular

Starshade rendezvous: exoplanet sensitivity and observing strategy

“…Imaging the dust disk distribution requires an integration time of 1 day (on average) or up to 4 days (maximum) to obtain a flux sensitivity of 0.1 zodi, enabling 5 − σ detection of disks as faint as 0.5 zodi. While disks this faint have never been observed (other than the SS, with 1 zodi), the median level inferred from a sample of nearby stars is 4.5 zodis, 11 suggesting that most, if not all, of the systems with HZ dust will be detected. With a telescope imaging resolution of 0.…”

“…The distribution of exozodiacal dust brightness, at the level relevant for Earth-like exoplanet detection, is largely unconstrained. Recent bounds on the warm dust disk brightness of many sunlike stars of interest to the SRP are provided by large binocular telescope interferometer (LBTI), 11 but the sensitivity is still more than an order of magnitude in excess of what is needed. Objective 2 will provide the key information necessary to assess the sensitivity to directly image HZ exoplanets.…”

“…Analysis of these upper limits suggests a median dust thickness a factor of 4.5 higher than that of the SS. 11 We adopt this enhanced level as our fiducial amount of exozodiacal dust. The exozodi model is scaled based on the ratio of stellar flux to solar flux and corrected for orbital location relative to Earth-equivalent insolation distance (EEID) given by 1 AU × ðL ⋆ ∕L ⊙ Þ 1∕2 .…”

“…For the exozodiacal dust environment, we assume a constant fiducial value of 4.5 zodi based on median dust thickness, a factor derived from LBTI limits and measurements. 11 Two targets of interest, epsilon Eridani and Vega, have measurements of warm dust disk brightness of 300 zodi and 33 zodi, respectively. These values are well in excess of 10 zodi, which significantly increases the integration time for detection of Earth-like planets and the risk of contamination from planet-induced disk structure.…”

An Empirical Mass–Radius Relation for Cool Giant Planets

“…Alternatively, an interferometer can be used to effectively suppress starlight. In contrast to a co-axial beam combiner, which is used for the Keck Interferometer (Millan-Gabet et al 2011;Mennesson et al 2014) and the Large Binocular Telescope Interferometer (Ertel et al 2018(Ertel et al , 2020, a multi-axial beam combiner maximizes the spatial resolution, e.g., the Palomar fiber nuller (PFN, Haguenauer & Serabyn 2006;Mennesson et al 2011;Serabyn et al 2019) and the Fizeau imaging mode at LBT (Spalding et al 2018). We will focus on the multi-axial interferometry because of its enhanced spatial resolution and its potential of feeding a high resolution spectrograph with a single-mode fiber.…”