Spitzer Microlensing parallax reveals two isolated stars in the Galactic bulge

Abstract

We report the mass and distance measurements of two single-lens events from the 2017 Spitzer microlensing campaign. The ground-based observations yield the detection of finite-source effects, and the microlens parallaxes are derived from the joint analysis of ground-based observations and Spitzer observations. We find that the lens of OGLE-2017-BLG-1254 is a $0.60\pm 0.03M_{\odot }$ star with $D_{\mathrm{LS}}=0.53\pm 0.11\text{kpc}$, where $D_{\mathrm{LS}}$ is the distance between the lens and the source. The second event, OGLE-2017-BLG-1161, is subject to the known satellite parallax degeneracy, and thus is either a $0.51_{-0.10}^{+0.12}{M}_{\odot }$ star with $D_{\mathrm{LS}}=0.40\pm 0.12\text{kpc}$ or a $0.38_{-0.12}^{+0.13}{M}_{\odot }$ star with $D_{\mathrm{LS}}=0.53\pm 0.19\text{kpc}$. Both of the lenses are therefore isolated stars in the Galactic bulge. By comparing the mass and distance distributions of the eight published Spitzer finite-source events with the expectations from a Galactic model, we find that the Spitzer sample is in agreement with the probability of finite-source effects occurrence in single lens events.

16 pages, 6 Figures. Submitted to AAS journal