Two Stars Two Ways: Confirming a Microlensing Binary Lens Solution with a Spectroscopic Measurement of the Orbit

TL;DR

This study confirms the orbital parameters of a binary lens system inferred from microlensing light curves through independent radial velocity measurements, validating microlensing orbital modeling techniques.

Contribution

It provides the first independent spectroscopic confirmation of orbital elements derived from microlensing data.

Findings

Radial velocity measurements match microlensing orbit predictions.

Confirmed the orbital parameters of OGLE-2009-BLG-020L.

Validated the use of spectroscopic follow-up for microlensing systems.

Abstract

Light curves of microlensing events involving stellar binaries and planetary systems can provide information about the orbital elements of the system due to orbital modulations of the caustic structure. Accurately measuring the orbit in either the stellar or planetary case requires detailed modeling of subtle deviations in the light curve. At the same time, the natural, Cartesian parameterization of a microlensing binary is partially degenerate with the microlens parallax. Hence, it is desirable to perform independent tests of the predictions of microlens orbit models using radial velocity time series of the lens binary system. To this end, we present 3.5 years of RV monitoring of the binary lens system OGLE-2009-BLG-020L, for which Skowron et al. (2011) constrained all internal parameters of the 200--700 day orbit. Our RV measurements reveal an orbit that is consistent with the predictions of the microlens light curve analysis, thereby providing the first confirmation of orbital elements inferred from microlensing events.