andy gould (ohio state)ppc07.physics.tamu.edu/menu/talk/may18/gould_elegant2.pdf · generation 0...
TRANSCRIPT
Microlensing: Elegant Tool for Astronomy and Physics
Andy Gould (Ohio State)
Outline● Brief History of Microlensing● Dark Matter● Precision Mass Measurements of Dark Objects● (Resolution of Stars on nanoarcsecond scales)● Planets
Generation 1● Liebes 1964, Phys Rev, 133, B835
● Many practical examples, including planets● Refsdal 1964, MNRAS, 128, 259
● Mass measurement of Isolated Star ● Refsdal 1966, MNRAS, 134, 315
● SpaceBased Parallaxes ● Paczynski 1986, ApJ, 304, 1
● Proposed First Practical Experiment
Generation 0● Eddington 1920, Space, Time, and Gravitation● Chwolson 1924, Astron. Nachr. 221, 329
● Einstein 1936a, Science, 84, 506 “Some time ago R.W. Mandl paid me a visit and asked me to publish the results of a little calculation, which I had made at his request .... there is no great chance of observing this phenomenon.”
● Einstein 1936b (private letter to Science editor) “Let me also thank you for your cooperation with the little publication, which Mister Mandl squeezed out of me. It is of little value, but it makes the poor guy happy.”
Generation 1: Einstein (1912)[Renn, Sauer, Stachel 1997, Science 275, 184]
Origin of First Microlensing Experiments● Alcock Seminar (Berkeley 1989)
● Bennett, Griest, Stubbs, etc ==> MACHO ● Rich (telephones Spiro) ==> EROS
● Paczynski contacts● Carnegie (Preston) ● Warsaw (Udalski etc) ==> OGLE
● Secret History of Alcock Seminar● Bennett moves from Princeton to Livermore ● Connects B.P. lensing with C.A. KBO search
Burst of Observational Results
● 1993: First lensing event MACHO LMC1
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● 1993: First bulge event OGLE #1
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● 1993: First binary event OGLE #7
● .
Many Effects Predicted by Theory
● Binaries/Planets (Mao & Paczynski 1991)
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● Parallax (Gould 1992)
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● Finite Source (Witt & Mao 1994)
● .
... Burst Continues ...
● 1995: First Parallax MACHO BLG 104C
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● 1997: First Finite Source MACHO Alert 9530
● .
Microlensing and Dark Matter
CMD of MACHO Events(Alcock et al. 2000, ApJ 542 281)
Contours: Halo Fraction vs Macho Mass
Optical Depth vs Selection SeverityImpact Parameter S/N Ratio
But ... EROS finds few events ... and only upper limits!
... and some “second bumps” that eliminate formerly “good events”
Tisserand & Milsztajn (Astroph/0501584)
To Probe Higher MACHO Masses:Use Wide Binaries
To Probe Higher MACHO Masses:Use Wide Binaries
Chaname & Gould 2004, ApJ 601 289
Big MACHOs But the observedwould destroy the halo binaries are awidest binaries perfect powerlaw
Big MACHOs Halobinaryruled out by poor limits complement
fit to power law microlensing
Yoo, Chaname & Gould 2004, ApJ 601 311
To Determine Lens Nature: SIM
MACHOLMC5Microlens Mass of an Isolated Star
Step 1: HST images lens and source
Alcock et al. 2001, Nature 414 617
Step 3:Measure microlens parallax from lightcurve.(+ Einstein radius)==> Mass and Distance
Step 4: Discover 'JerkParallax' Degeneracy
Gould 2004, ApJ 2004 606 319
Implies that very different trajectories can generate the same lightcurve.
Step 5: Get New ACS Images
Drake, Cook, & Keller 2004, ApJ 607 L29
Step 6: Redo microlens parallax
measurement
... to derive more precise mass and distance
Gould, Bennett & Alves 2004, ApJ 614 404
... or, more immediately: Spitzer
From a paper written 8 years ago ...
OGLE2005SMC001 CMD Photometry
Spitzer Obs
Nature's CurveballBinarylens Fit Singlelens Fit
Subo Dong
HALO favored over SMC
How Microlensing Finds Planets
First Microlens Planet:OGLE2000BLG235/MOA2000BLG53
How Do We Know It's a Planet?
Bond et al. 2004ApJ 606 L155
2nd Microlensing Planet
The New Zealand ConnectionGrant, Ian, Jennie, Phil
Amateurs + Professionals "It just shows that you can be a mother, you can work fulltime, and you can still go out there and find planets."
Jennie McCormick (Amateur Astronomer, Auckland, New Zealand)
OGLE2005BLG169:COLD NEPTUNE in HiMag Event
Deokkeun An
HOW DO WE KNOW IT'S A PLANET?
● 7 model parameters t0,u0,tE,b,q,alpha,rho
● 7 pronounced features ● >3 from full curve
(height, width, center)● >4 from perturbation
(2 kink times, height and width of bump)
Planet Distribution:The Conventional View
Equilibrium Temperature:The Unconventional View
Conclusions● MACHO Dark Matter
constrained to 20% of less● Planets now being discovered
with microlensing● First mass measurement of an
isolated star