WISE 12 micron search for exozodi candidates within 10 parsecs

Abstract

The discovery of extra-terrestrial life is one of the ultimate goals for future exoplanet-seeking missions, with one major challenge being the presence of 'exozodiacal' dust near target stars or within their habitable zone. Therefore, it is critical to identify which stars possess exozodiacal dust and quantify their emission levels. In this study, we conducted a search for exozodi candidates within 10 parsecs using the Reyl'e sample. We performed proper motion calculations and cross-matched the sample with the WISE and 2MASS database, resulting in 339 preliminary target samples. We further analysed the infrared radiation characteristics of these targets, using spectral energy distribution (SED) fitting to predict photometric flux levels in the infrared and searching for 3sigma excesses in the WISE W3 band. During further selection processes, we applied various analysis methods to perform rigorous validation. We identified five exozodi candidates all of which are brown dwarfs (BDs). Given the clustering in candidate spectral types, we expect that these are not true exozodi candidates, rather the apparent excess arises from the inability of the BD photosphere models to accurately represent the SEDs of objects at the L-T transition. Indeed, for the object DENIS J025503.3-470049, excess is likely due to silicate clouds in the BD atmosphere. We suggest that a more stringent 5sigma excess is required to infer excess for this spectral type. The detection rate (0/339) in our sample shows that less than 1% M stars have exozodi above 21% excess levels. This is consistent with the rate of exozodi at similar level towards FGK stars in the Kennedy & Wyatt sample (25/24,174). We provide upper limits on the 12 micron exozodi emission for the sample, which is typically at 21% relative to the star. For most stars, in particular the low mass M stars, this is the first such upper limit in the literature.