Abstract
We have designed and built the first band-limited coronagraphic mask used for ground-based high-contrast imaging
observations. The mask resides in the focal plane of the near-infrared camera PHARO at the Palomar Hale
telescope and receives a well-corrected beam from an extreme adaptive optics system. Its performance onsky
with single stars is comparable to current state-of-the-art instruments: contrast levels of ∼10−5 or better
at 0.
8 in Ks after post-processing, depending on how well non-common-path errors are calibrated. However,
given the mask’s linear geometry, we are able to conduct additional unique science observations. Since the
mask does not suffer from pointing errors down its long axis, it can suppress the light from two different stars
simultaneously, such as the individual components of a spatially resolved binary star system, and search for faint
tertiary companions. In this paper, we present the design of the mask, the science motivation for targeting binary
stars, and our preliminary results, including the detection of a candidate M-dwarf tertiary companion orbiting the
visual binary star HIP 48337, which we are continuing to monitor with astrometry to determine its association.
