A Census of Planets in the Globular Cluster M22 and the Galactic Bulge

Details A Census of Planets in the Globular Cluster M22 and the Galactic Bulge A Census of Planets in the Globular Cluster M22 and the Galactic Bulge

Jul 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001hst..prop.9061s&link_type=abstract

HST Proposal ID #9061

Physics

Hst Proposal Id #9061 Stellar Populations

Scientific paper

We propose a program of intensive monitoring of the globular cluster M22 and its background Galactic bulge field, using both WFPC2 and simultaneous parallel STIS imaging. In an earlier pilot program to look for microlensing events due to M22, we detected one long- duration event {lens mass of 0.25 M_solar}, and 11 candidate short-duration {<0.4 days} events corresponding to lens masses of <0.25 Mjup. This suggests the startling possibility that a non-negligible fraction of the cluster mass resides in free-floating, sub-Jupiter mass objects. However, each of the 11 events was seen only as a single brightening, due to the wide spacing of the observations. In order to follow up on this potentially important discovery, we propose to observe two fields in the core of M22 continuously with WFPC2 over a 7-day interval {92 orbits}, followed by an additional 31 orbits spaced out over the ensuing 13 days. Based on the pilot study, we expect to detect 10-25 short-duration microlensing events, which will be well sampled and will yield lens masses. We will simultaneously observe a bulge field with STIS imaging, in order to detect planetary transits. Depending on the frequency of planets and its metallicity dependence, we should detect 3-15 planetary transits among the bulge stars. Byproducts will be a search for planets around the M22 stars, and a census of variable stars and binaries in both the cluster and the bulge.

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