Speckle Imaging Excludes Low-Mass Companions Orbiting the Exoplanet Host   Star TRAPPIST-1
  We have obtained the highest resolution images available of TRAPPIST-1 using the Gemini-South telescope and our speckle imaging camera. Observing at 692 and 883 nm, we reached the diffraction limit of the telescope providing a best resolution of 27 mas or, at the distance of TRAPPIST-1, a spatial resolution of 0.32 AU. Our imaging of the star extends from 0.32 to 14.5 AU. We show that to a high confidence level, we can exclude all possible stellar and brown dwarf companions, indicating that TRAPPIST-1 is a single star. 
Steve B. Howell, Mark E. Everett, Elliott P. Horch, Jennifer G.   Winters, Lea Hirsch, Dan Nusdeo, Nicholas J. Scott
astro-ph.EP astro-ph.SR