Resolving the Young 2 Cygni Run-away Star into a Binary using iLocater

TL;DR

This paper demonstrates the use of the iLocater AO-fed spectrograph on the LBT to resolve the binary nature of the young runaway star 2 Cygni, showcasing high spatial resolution and potential for studying stellar multiplicity.

Contribution

First-light observations with iLocater's SX camera successfully resolved a binary companion of 2 Cygni, illustrating AO capabilities for high-resolution spectroscopy and binary detection.

Findings

Detected a candidate companion star at 70 mas separation.

Confirmed the companion with follow-up AO imaging in multiple filters.

Obtained spatially resolved spectra indicating similar spectral types.

Abstract

Precision radial velocity (RV) spectrographs that use adaptive optics (AO) show promise to advance telescope observing capabilities beyond those of seeing-limited designs. We are building a spectrograph for the Large Binocular Telescope (LBT) named iLocater that uses AO to inject starlight directly into single mode fibers (SMF). iLocater's first acquisition camera system (the `SX' camera), which receives light from one of the 8.4m diameter primary mirrors of the LBT, was initially installed in summer 2019 and has since been used for several commissioning runs. We present results from first-light observations that include on-sky measurements as part of commissioning activities. Imaging measurements of the bright B3IV star 2 Cygni ($V=4.98$) resulted in the direct detection of a candidate companion star at an angular separation of only $\theta = 70$ mas. Follow-up AO measurements using Keck/NIRC2 recover the candidate companion in multiple filters. An $R\approx1500$ miniature spectrograph recently installed at the LBT named ``Lili'' provides spatially resolved spectra of each binary component, indicating similar spectral types and strengthening the case for companionship. Studying the multiplicity of young runaway star systems like 2 Cygni ($36.6 \pm 0.5$ Myr) can help to understand formation mechanisms for stars that exhibit anomalous velocities through the galaxy. This on-sky demonstration illustrates the spatial resolution of the iLocater SX acquisition camera working in tandem with the LBT AO system; it further derisks a number of technical hurdles involved in combining AO with Doppler spectroscopy.