1. Microlensing with CCDs
Philip Yock
University of Auckland, NZ
NZ-Australia Semiconductor Instrumentation Workshop, June 2004

2. Why microlensing? – Why CCDs?
Precision measurements can be made on stars
Highest precision measurements on planets
Many stars must be monitored – CCDs essential

3. Basics of microlensing
Source
Earth
EINSTEIN RING

4. Demonstration with a glass lens
Courtesy Sidney Liebes, Princeton

5. Typical astronomical dimensions
10,000 ly
20,000 ly
2 AU
1 mas

6. Detectable in the Galactic Bulge

7. Required separation ~ 1mas, but typical separation ~1as
The need for CCDs
Required separation ~ 1mas, but typical separation ~1as
“No chance of observing this phenomenon” - Einstein (1936)

8. Typical CCD arrays
MOA-II
MOA-I
24 million pixels
80 million pixels

9. Difference imaging essential from the ground
Ground versus space
MACHO 98-BLG-35
HST
MOA
Difference imaging essential from the ground

10. Typical transverse velocity ~ 200 km/sec
Light curve
Typical transverse velocity ~ 200 km/sec

11. Liebes-Paczynski light curve versus data

12. Planetary microlensing
Planets perturb the Einstein ring

13. Comparison with Rutherford scattering

14. Planetary perturbations
Neptune at 2 AU
Perturbation ~ 5%

15. Neptune at ~ 2AU at different 

16. Earth at ~ 2 AU
Perturbation ~ 0.5%

17. Two planets
Detectable if  > 20°

18. MACHO 98-BLG-35
 Magnification = 80
 Possible Earth-mass planet

19. MOA 2003-BLG-32/OGLE 2003-BLG-219 Magnification = 520
e-4 = Neptune e-5 = Earth
e-6 = Mars
(preliminary)

20. MOA 2003-BLG-32/OGLE 2003-BLG-219
e-4 = Neptune
e-3 = Saturn

21. Binary lens
A “caustic” is formed

22. MOA 2002-BLG-33 Wise 1m 20 exp MOA 0.6m 480 exp HST 2.4m 5 exp EROS 1m
MDM
2.4m
260 exp
HST
2.4m
5 exp
EROS 1m
186 exp
Boyden
1.5m
473 exp

23. MOA 2002-BLG-33  The light curve determines the lens geometry
 The lens profiles the source

24. MOA 2002-BLG-33  Caustic crossed in 15.6 hours
 Profiles obtained, on entry and on exit

25. Stellar profile  Stellar atmosphere theory confirmed
MOA 2002-BLG33
Another star
 Stellar atmosphere theory confirmed
 Precision comparable to that of the VLTI - Very Large Telescope Interferometer at ESO

26. Conclusions  Stellar gravitational lenses exist
 Extra-solar planets detectable
 Stars resolvable
 Nature helpful!

27. 64 million dollar question
Is SU(3)SU(2)U(1) being studied on other planets?

28. Acknowledgements  Ian Bond & Nick Rattenbury
 John Hearnshaw & Yasushi Muraki
 Colleagues in MOA, MACHO, EROS, OGLE, FUN, PLANET
 Marsden Fund, Department of Education of Japan