GTC/CanariCam deep mid-infrared imaging survey of northern stars within 5 pc

Abstract

In this work we present the results of a direct imaging survey for brown dwarf companions around the nearest stars at the mid-infrared 10 micron range (λ c = 8.7 µm, ∆λ = 1.1 µm) using the CanariCam instrument at the 10.4 m Gran Telescopio Canarias (GTC). We imaged the 25 nearest stellar systems within 5 pc of the Sun at declinations δ > −25 • (at least half have planets from radial velocity), reaching a mean detection limit of 11.3 ± 0.2 mag (1.5 mJy) in the Si-2 8.7 µm band over a range of angular separations from 1 to 10 arcsec. This would have allowed us to uncover substellar companions at projected orbital separations between ∼2 and 50 au, with effective temperatures down to 600 K and masses greater than 30 M Jup assuming an average age of 5 Gyr and down to the deuterium-burning mass limit for objects with ages <1 Gyr. From the non-detection of such companions, we determined upper limits on their occurrence rate at depths and orbital separations yet unexplored by deep imaging programs. For the M dwarfs, main components of our sample, we found with a 90% confidence level that less than 20% of these low-mass stars have L and T-type brown dwarf companions with m 30 M Jup and T eff 600 K at ∼3.5-35 au projected orbital separations.