WISE 12um exozodi candidates within 10pc

We identified 5 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% of 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.