Scientific Colloquium
March 9, 2007

"Worlds in Transit"

More than 200 extrasolar planets discovered so far, all of them around
relatively nearby stars. The SWEEPS(Sagittarius Window Eclipsing Extrasolar
Planet Search) project used HST to monitor 180,000 stars in the Galactic bulge
continuously for 7 days to look for transiting extrasolar planets. The SWEEPS
sample represents the farthest such sample, and includes stars down to 0.45
solar mass. We discovered 16 candidates with orbital periods between 0.4 and
4.2 days. In two cases, radial-velocity measurements support the planetary
nature of the companions. Five candidates are ultra-short-period planets
(USPPs) with orbital periods below 1.0 day, something that had not been seen
before, and which occur only around stars of less than 0.88 solar mass. This
indicates that those orbiting very close to more luminous stars might be
evaporatively destroyed, or that jovian planets around lower-mass stars might
migrate to smaller radii. The resulting frequency of planets in the Galactic bulge
is similar to that in the solar neighborhood.

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