Imaging faint brown dwarf companions close to bright stars with a small, well-corrected telescope aperture

TL;DR

This study demonstrates that a small, well-corrected telescope with a phase-mask coronagraph can effectively image faint brown dwarf companions near bright stars, achieving contrast levels comparable to larger telescopes with advanced adaptive optics.

Contribution

The paper introduces the use of a 1.6 m off-axis telescope with a phase-mask coronagraph for detecting close-in brown dwarf companions, showing its effectiveness for initial surveys.

Findings

Detected brown dwarf companions around three stars.

Identified a new potential brown dwarf or low-mass star near HD171488.

Achieved contrast comparable to larger telescopes with current AO systems.

Abstract

We have used our 1.6 m diameter off-axis well-corrected sub-aperture (WCS) on the Palomar Hale telescope in concert with a small inner-working-angle (IWA) phase-mask coronagraph to image the immediate environs of a small number of nearby stars. Test cases included three stars (HD 130948, HD 49197 and HR7672) with known brown dwarf companions at small separations, all of which were detected. We also present the initial detection of a new object close to the nearby young G0V star HD171488. Follow up observations are needed to determine if this object is a bona fide companion, but its flux is consistent with the flux of a young brown dwarf or low mass M star at the same distance as the primary. Interestingly, at small angles our WCS coronagraph demonstrates a limiting detectable contrast comparable to that of extant Lyot coronagraphs on much larger telescopes corrected with current-generation AO systems. This suggests that small apertures corrected to extreme adaptive optics (ExAO) levels can be used to carry out initial surveys for close brown dwarf and stellar companions, leaving followup observations for larger telescopes.