A Reexamination of the ``Planetary'' Lensing Events in M22

Abstract

We have carried out a further analysis of the tentative, short-term brightenings reported by Sahu and coworkers, which were suggested to be possible lensing of Galactic bulge stars by free-floating planets in the globular cluster M22. Closer examination shows that-unlikely as it may seem-small, pointlike cosmic rays had hit very close to the same star in both of a pair of cosmic-ray split images, and this caused the apparent brightenings of stars at the times and locations reported. We show that the observed number of double hits is consistent with the frequency of cosmic rays in WFPC2 images, given the number of stars and epochs observed. Finally, we point to ways in which cosmic rays can be more directly distinguished. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.