# The Radial Velocity of OGLE-2015-BLG-0966S

## TL;DR

This study measures the radial velocity of a microlensing source star to help determine its location, demonstrating that even low-quality spectra can yield valuable information for characterizing such stars.

## Contribution

It presents a method to use radial velocity measurements from low signal-to-noise spectra to infer the bulge membership of microlensing source stars.

## Key findings

- Radial velocity measured as 53 +/- 1 km/s supports bulge location.
- Measurement was inconclusive for the source's nature.
- Shows low S/N spectra can inform microlensing studies.

## Abstract

The distance to the planetary system OGLE-2015-BLG-0966L and the separation between the planet and its host star are ambiguous due to an ambiguity in the distance to the source star (Street et al. 2016). We attempt to break this degeneracy by measuring the systemic radial velocity of the source star measured from a spectrum taken while the source was highly magnified. Our measurement of v_{LSR} = 53 +/- 1 km s^{-1} does not definitively resolve the nature of the source, but supports the general conclusion that the source is in the bulge. Although in this case the measured radial velocity was inconclusive, this work demonstrates that even a low signal-to-noise spectrum can provide useful information for characterizing microlensing source stars.