The Companions to B and A Stars Snapshot (CBASS) Survey: Initial Detections of Low-Mass M Dwarf Companions to Young B and A Stars

We present results from the ongoing Companions to B and A Stars Snapshot (CBASS) Survey, a high-resolution demographics survey for low-mass companions around nearby B and A stars using adaptive optics imaging from NIRC2 on the Keck II telescope. This survey allows for identification and characterization of brown dwarfs and low-mass M dwarfs in the intermediate stages of evolution, as the ages of the stars in our population sample, being B and A stars, have relatively short main sequence lifetimes. The brown dwarfs detected through this study will provide a critical comparison to directly imaged star–planet systems and their atmospheres. Through this large survey, the goal of which is to measure the demographics of brown dwarf companions to intermediate mass stars, we are aiming to expand the number of confirmed companion brown dwarfs. With a sufficient sample of wide-separation brown dwarf companions, we can quantify the location of the break between star and planet formation around these intermediate-mass stars, and determine the differences in formation and evolution between star–star, star–brown dwarf, and star–planet binaries. We completed a first-epoch companion search around over 200 young B and A stars within 200 pc, identifying over 170 candidate brown dwarf and low-mass M dwarf companions for follow up confirmation and characterization. We will discuss results from ongoing 2nd-epoch observations of our targets marked for follow up, including the discovery of at least six new M-dwarf companions. Through our observations and data reduction methods, we are able to detect candidate companions that are ~15 magnitudes fainter than their host stars at distances beyond 1”, allowing us the sensitivity to detect wide-separation brown dwarfs. We will present the current status of this ongoing survey, including the results for confirmed companions.