Dr. John Greenhill - University of Tasmania
    Wednesday, January 14th 2004, at 14:00


       The PLANET microlensing collaboration

Gravitational microlensing can be used to search for planetary companions
to the lensing star. It has maximum sensitivity for detection of
Jupiter-mass planets with orbital radii similar to that of Jupiter and
hence is complementary to the radial velocity and transit techniques. The
caustic structure produced by binary lenses leads to a strong gradient of
magnification across the disc of the source star. Hence microlensing
involving binary lenses can be used to obtain radial brightness profiles
of the source star. As the caustic scans across the disc, high resolution
spectroscopy can provide even more detailed information about the stellar
atmosphere. The PLANet (Probing Lensing Anomalies Network) collaboration
uses 1 m class telescopes in South Africa, Australia and Chile to make
high time resolution, around the clock, photometric measurements of
selected microlensing events. On several occasions PLANET has used the ESO
VLT to make spectroscopic measurements during binary lens events.

In this talk I will describe the microlensing technique, current limits
set by PLANET on planetary companions to lens stars and recent photometry
and spectroscopy of a G5III giant in the Galactic Bulge. Our measurements
are not consistent with simple limb darkening profiles or with synthetic
spectra based on current stellar atmospheric models.