MOA, Microlensing Observations in Astrophysics Bennett
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Nov 4 2010  I hear DAVID BENNETT today... 3rd floor clonf room of KAVLI  at SLAC.
 
spectroscopy of nearby earths might show life
 
radial veloctiy ,,,   changes cause red and blue shift of light from  star ... most common method of
detecting exoplanets  a la  Geoff Marcy..
 
Kepler good for short period orbits.
mostly HOT, INNer planets  (short period)
 
direct detection is rare and hard to do.
 
Keck  angular differential imaging  ??
do subtraction to get rid of starlight... only works for v young planets,
say with < 104 difference in brightness btwn star and planet.
 
he shows graph with Y axis of  earth masses from  0.1  to 103 and above
X axis  is  semi-major axis  in AU from 0.001 to  100 AU  both r log scales.
 
so,  how big the planet in earth masses on the Y axis
and how far away is the planet from its star on X axis.
 
Most detected planets are  really  big and close in.
 
this is a great and key graph with all known exoplanets  he shows  perhaps a 1000 points.
 
microlensing is best for  AU =1 and mass = 1
 
he shows dopplers in black  (most of these and the Kepler ones are all in the v heavy  quadrant and most are
v v close to their star... so these all crowd into the upper L of the graph.
 
next graph is normalized to the snowline .. which is defined to be  2.7 AU  (permanent liquid water/ methane/ammonia
even at v low pressure)
but this is at 10 million years after they form.
 
detection efficiencies for planets is a function of how big they are and how close in they are.
 
can use to estim how prevalent the planets r.
 
Saturn mass planets are present in abt 1/3 of the systems.
 
11 published discoveries from microlensing.
 
get weird lensing if u have a big planet.
 
magnification determined by caustics.
 
planetary caustics.
 
look at that time when magnification is highest;  (ie when there is the most lensing for that object)
he repeatedly shows a beautiful video of the kind of signal they look for....
its like passing a marble thru the bottom of a wine glass where at some point get rapidly changing image.
 
einstein 1936 ... gravit lensing  einstein rings.
 
if sl offset then see major image  (bigger arc) and minor
 
resol is 1 arc sec
 
ogle=2005-blg-390lb  was lowest mass exoplanet seen by microlensing.
 
in galactic bulge, only 2 stars in a million are actual being microlenses.
therefore u need to look at lots of stars.
 
MOA-II  1.8 m telescope
in New Zealnad.
 
OGLE = optical grav lens experiment.
polish group.
 
galactic bulge is 30  degr S of the equator ... thats where they look,
so these r all located in S hemisphere.
 
amateur astronomers r v helpful  cuz they just wait for big mag event.
 
einstein radius crossing time   t sub E  is the main thing u observe.
 
can calculate mass when u can get  angular einstein radius (can do that if u have separated observers)
 
ogle-2006-blg-109lb,c    (jupiters and saturns around a star)
 
"saturn " gives a lrg caustic cuz its close to einstein ring...  jupiter is further away, so smaller signal.
 
Why space-based microlensing
 
typical  lens-source relative proper motion is  only abt  5 mas per year , ie milliarcsecs per year.
 
lens star has difft color than the source star.
 
curve of detection moves way way down  toward v v low mass planets  when moved into space.
 
mpf   vs  kepler
 
rocks with no volatiles is bad;   for life  want  rocks + volatiles  (water etc)
 
want ir detectors for  mpf focal plane concept.  infrared is best.
 
MPF  combined with jdem-omega dn NISS by decadal survey to make wfirst.
 
??  merge with esa-euclid??
 
videos by d. bennett   showing microlensing of a traversing planet.
 
kepler.. main noise source r   sunspots  travelling around imitating a planet.
 
 
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