Spitzer Microlensing Program as a Probe for Globular Cluster Planets. Analysis of OGLE-2015-BLG-0448

Understand

The microlensing event OGLE-2015-BLG-0448 was observed by Spitzer and lay within the tidal radius of the globular cluster NGC 6558.

• The event had moderate magnification and was intensively observed, hence it had the potential to probe the distribution of planets in globular clusters.
• We measure the proper motion of NGC 6558 ($\mu_{\rm cl}$(N,E) = (+0.36+-0.10, +1.42+-0.10) mas/yr) as well as the source and show that the lens is not a cluster member.
• Even though this particular event does not probe the distribution of planets in globular clusters, other potential cluster lens events can be verified using our methodology.