On-Sky Demonstration of a Linear Band-limited Mask with Application to Visual Binary Stars

TL;DR

This paper reports the first on-sky use of a linear band-limited coronagraphic mask for ground-based high-contrast imaging, demonstrating its ability to suppress starlight and enable unique observations of binary star systems.

Contribution

The paper introduces a novel linear band-limited mask for high-contrast imaging, enabling simultaneous suppression of light from binary stars and detection of faint companions.

Findings

Achieved contrast levels of ~10^{-5} at 0.8" in Ks band

Successfully detected a candidate tertiary companion to a binary star

Demonstrated the mask's capability for simultaneous binary star observation

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 on-sky with single stars is comparable to current state-of-the-art instruments: contrast levels of $\sim10^{-5}$ or better at 0.8" in $K_s$ 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.