A Close Companion Search around L Dwarfs using Aperture Masking Interferometry and Palomar Laser Guide Star Adaptive Optics

TL;DR

This study uses aperture masking interferometry with Palomar laser guide star adaptive optics to search for close companions around early-L dwarfs, detecting candidate binaries and demonstrating the technique's effectiveness for high-resolution binary detection.

Contribution

First application of aperture masking with laser guide star adaptive optics at Palomar, introducing new analysis techniques for low signal-to-noise data and revealing potential underestimation of tight-separation binaries.

Findings

Detected four candidate binaries with 90-98% confidence.

Two binaries have projected separations less than 1.5 AU.

Found two candidate binaries among previously observed targets.

Abstract

We present a close companion search around sixteen known early-L dwarfs using aperture masking interferometry with Palomar laser guide star adaptive optics. The use of aperture masking allows the detection of close binaries, corresponding to projected physical separations of 0.6-10.0 AU for the targets of our survey. This survey achieved median contrast limits of Delta_K ~ 2.3 for separations between 1.2 - 4 lambda/D, and Delta_K ~ 1.4 at (2/3)lambda/D. We present four candidate binaries detected with moderate to high confidence (90-98%). Two have projected physical separations less than 1.5 AU. This may indicate that tight-separation binaries contribute more significantly to the binary fraction than currently assumed, consistent with spectroscopic and photometric overluminosity studies. Ten targets of this survey have previously been observed with the Hubble Space Telescope as part of companion searches. We use the increased resolution of aperture masking to search for close or dim companions that would be obscured by full aperture imaging, finding two candidate binaries. This survey is the first application of aperture masking with laser guide star adaptive optics at Palomar. Several new techniques for the analysis of aperture masking data in the low signal to noise regime are explored.