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Planetary Microlensing for dummies

Planetary Microlensing for dummies. Nick Cowan April 2006. Outline. Microlensing: it’s hard Results: it works Prospects: it’s useful, too. Deflecting Light. Einstein predicted that massive objects bend light. He was right. Microlensing.

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Planetary Microlensing for dummies

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  1. Planetary Microlensingfor dummies Nick Cowan April 2006

  2. Outline • Microlensing: it’s hard • Results: it works • Prospects: it’s useful, too

  3. Deflecting Light • Einstein predicted that massive objects bend light. • He was right.

  4. Microlensing • If the source is small and far away, we cannot resolve the multiple images. • The extra images manifest themselves as a brightening of the source. • If the lens consists of multiple point masses, there are regions of infinite magnification known as caustics.

  5. Caustic Crossing High Magnification

  6. Caustic Crossing Event High Amplification Event

  7. Step 1: The Detection • July 11th 2005: The OGLE Early Warning System announces microlensing event. • July 31st: Maximum magnification. • August 9th: Deviation from single lens. Source star: RStar = 9.6 Rsun G4 III (K giant)

  8. Step 2: The Analysis 2 = 562.26 650 data points • 7 lens parameters • 12 flux normalization parameters = 631 degrees of freedom Reduced 2 = 0.89

  9. More Analysis • Use four different lens modelling codes just to be sure. • Best single-lens model has ∆2 = 46 for one less model parameter. • Microlensing only directly determines the planet-star mass ratio, q, and projected separation, d. • Use Galactic models and Bayesian statistics to get the quantities of real interest (Mp and a).

  10. Summary of Results • Five probable planetary microlensing events have been observed so far: • MACHO-98-BLG-35 • OGLE-2003-BLG-235/MOA-2003-BLG-53 • OGLE-2005-BLG-071 • OGLE-2005-BLG-390 • OGLE-2006-BLG-169

  11. How to detect an Earth (with current technology) • Stare at the Galactic Bulge: there are lots of stars in that direction. • Keep your fingers crossed: it’s pretty unlikely that any given star will get lensed. • Don’t blink: The planet-induced deviation from single-lens behavior takes place in mere hours, while the overall lensing event takes months.

  12. Future Prospects • MOA-2 • 1.8 m telescope dedicated to microlensing • 2.2 sqr degree field of view • 23 fields, multiple times per night • Earth-Hunter Network • Four 2 m class telescopes at different longitudes • 4 sqr degree f.o.v • A few fields per night • Microlensing Planet Finder • Space telescope capable of continuous observations

  13. Summary • Microlensing is a viable way to detect terrestrial planets and icy giants with a > 1AU. • The mass ratio and projected distance between the primary and secondary lens are readily determined. • The actual mass and semi-major axis of the planet are inferred from models. • An arbitrarily high signal-to-noise can be achieved, one just has to be lucky. • Follow up studies are difficult. • Microlensing probes an area of M-a space which is largely unexplored.

  14. References • Rattenbury, astro-ph/0604062 • Beaulieu et al., Nature (Jan 2006) • Queloz, Nature (Jan 2006)

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