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 ($\hat{I}{»}_c$=8.7$\hat{I}¼$m, $\hat{I}”\hat{I}»$=1.1$\hat{I}¼$m) 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 $\hat{I}´>-25^{\circ }$ (at least half have planets from radial velocity), reaching a mean detection limit of 11.3$\pm$0.2 mag (1.5 mJy) in the Si-2 8.7$\hat{I}¼$m 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 $\sim$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 $m\gtrsim 30M_{Jup}$ and $T_{eff}\gtrsim$ 600 K at $\sim$3.5--35 au projected orbital separations.

28 pages, 9 figures, accepted for publication in ApJ