Download lec06_07oct2011

What (exo)-planetary science can be
done with microlensing?
Ge/Ay133
Other routes to Earth-like planets?
α = 4GM/bc2
b
Microlensing example:
Microlensing example:
Best geometry uses stars at a few kpc (the lens)
against the Galactic Bulge (light source).
5.5 MEarth planet at 2.6 AU
around a M-dwarf (0.22 M)
primary at 6.6 ± 1.0 kpc.
J.-P. Beaulieu et al. Nature 439, 437-440 (26Jan2006)
Magnification map of the lensing system in
OGLE 2003-BLG-235/MOA 2003-BLG-53.
Biggest perturbation
when planet is near
Einstein ring AND
the location of the
background stellar
image (so, some/
many planets missed).
I.A. Bond et al. 2004,
ApJ, 606, L155
OGLE 2003-BLG-235/MOA 2003-BLG-53
Animations:
I.A. Bond et al. 2004, ApJ, 606, L155
Are there Earth-like planets beyond the snow-line?
Something like ten systems so far, +’s/-’s ?
Advantages of the microlensing technique to detect exoplanets include:
* More sensitive than most other techniques to small-mass planets (like Earth)
* Most sensitive to planets in our Galaxy that have orbit sizes of a few
astronomical units (like those of Mars or Jupiter)
* Only method capable of detecting planets in other galaxies
* The most common stars in the Galaxy will be the most likely lenses
* Capable of detecting (with some probability) multiple planets in a single
lightcurve.
In summary, the microlensing can be used to study the statistical abundance of
exoplanets in our Galaxy with properties similar to the planets in our own Solar
System.
Something like ten systems so far, +’s/-’s ?
Disadvantages of the microlensing technique to detect exoplanets include:
* Millions of stars must be monitored to find the few that are microlensing
at any given time
* Planetary deviations in lightcurve are short-lived and could be missed
due to inopportune timing
* Substantial probability that any planet will not be detected in lens
system, even if present
* Deviations in microlensing lightcurves due to planets will not repeat
(as they are due to a chance alignment)
* Planetary parameters (such as mass, orbit size, etc) depend on the
properties of the host star, which are typically unknown
In sum, the microlensing technique requires intensive use of telescope time,
and is unsuitable for continued detailed study of individual exoplanets.