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

TL;DR

This study used mid-infrared imaging with GTC/CanariCam to search for brown dwarf companions around the nearest stars within 5 parsecs, setting new upper limits on their occurrence at specific orbital separations.

Contribution

First deep mid-infrared imaging survey targeting the closest stars within 5 pc, establishing upper limits on brown dwarf companion frequency at 8.7μm.

Findings

No brown dwarf companions detected within the survey limits.

Less than 20% of M dwarfs have L and T-type brown dwarf companions at 3.5-35 au.

Achieved detection limits down to 600 K and 30 M_Jup for potential companions.

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