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Advancements in Microlensing Planet Surveys: Challenges and Opportunities

This article discusses the evolution of microlensing planet surveys and addresses the complexities and challenges encountered in this field. Led by Dan Maoz from Tel-Aviv University, the second generation of microlensing studies, which includes contributions from Yossi Shvartzvald and collaborations with OGLE, MOA, and microFUN, is examined. Key issues, such as survey strategies, detection efficiencies, and the rarity of observable planetary events, are outlined, along with the promising future of continuous monitoring and enhanced observational techniques.

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Advancements in Microlensing Planet Surveys: Challenges and Opportunities

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  1. Microlensing planet surveys: the second generation Dan Maoz Tel-Aviv University with Yossi Shvartzvald, OGLE, MOA, microFUN

  2. Conceived problems with microlensing: • Seems complicated… • and hence results suspect… • No “follow up” of planets possible • 4. Statistically useless due to haphazard survey strategies • 5. Planet yield so small -- not worth trouble?

  3. a R

  4. I E S DLS DOL DOS a R

  5. “microlensing” (in our Galaxy): In distant galaxies: “macrolensing”, “galaxy lensing”: cluster lensing:

  6. I E S DLS DOL DOS a R

  7. I+ S + b A - I- DLS DOL DOS a R I+S + SA = I+A

  8. ~milliarcsec

  9. Magnification=image area / source area : magnification ~ 1/ (impact parameter)

  10. Einstein-ring crossing timescale: t =E DOL / v ~ M1/2 S. Gaudi • ForDOL=8 kpc, • v=20 km/s • t(1Msun) = 2 months • t(1MJ)=2 days

  11. The first microlensing lightcurves (LMC) Alcock et al. 1993

  12. Nowadays, ~1000 microlensing events/yr detected toward Galactic bulge Yee+ 09

  13. Bond et al. 2004

  14. Beaulieu et al. 2006

  15. Udalski et al. 2005

  16. Gould et al. 2006

  17. Gaudi et al. 2008 “Jupiter”+”Saturn” system: 1+2+3+5=“Saturn”, 4=“Jupiter”

  18. Our solar system: 5.2 AU 9.5 AU 1 Msun 1 Mjup 1 Msat Msat/Mjup = 0.30 Rjup/Rsat = 0.55 Mc/Mb = 0.37 Rb / Rc = 0.50 OGLE-2006-BLG-109L,b,c: 2.3 AU 4.6 AU 0.50 Msun 0.71 Mjup 0.90 Msat

  19. Second 2-planet system discovered: 0.7MJ (4.6 AU) and 0.1MJ (3.8 AU) Han+2012, OGLE-2012-BLG-0026

  20. Simulation by S. Gaudi

  21. Simulation by S. Gaudi

  22. q = Mp / Mhost Simulation by S. Gaudi

  23. Caustics: points in the source plane which get infinite magnification. For a point lens, caustic is a single point behind the lens. (source there gets magnified into Einstein ring)

  24. Caustic cusps

  25. Magnification still ~ 1/(distance to caustic)

  26. Source passage on or near central caustics: high mag  almost full Einstein ring  ~100% detection efficiency for planets near Einstein radius (lensing region). planetary caustics: low mag  Lower planet detection efficiency per event, but much more common. A. Cassan

  27. Microlensing probes a unique region of planetary parameter space… Gould et al. 2006, 2009

  28. …near the Einstein radii of stars ~ their snow lines. Gould et al. 2006, 2009 Snowline scaling with mass: star

  29. Snowline-region planet frequency based on microlensing discovery statistics: Gould et al. (2010, based on 6 planets): ~1/3 of stars have snowline-region planets; ~1/6 of stars have solar-like planetary systems; Cassan et al. (2012, based on 2 (!) planets): ~1/6 host jupiters ~1/2 host neptunes ~2/3 host super-earths

  30. To date, only ~20 microlensing planets. Why so few? “1st Generation” survey strategy (Gould & Loeb 1992) focused on bright, high-magnification (mag>100) events.

  31. Udalski et al. 2005 Gould et al. 2006 Gaudi et al. 2008

  32. 1st Generation microlensing • low cadence (~ once a night) OGLE, Chile, 1.3m MOA, NZ, 1.8m

  33. 1st Generation microlensing

  34. 1st Generation microlensing ~ 650 events/year

  35. 1st Generation Microlensing Follow-up search for planetary perturbations with global network on bright, high-magnification events:

  36. High-magnification (mag >100) events are: Good: ~100% sensitivity to planets projected near Einstein radius, + high S/N light curves even with small and amateur telescopes. Bad: Rare events (~1%)  ~7 events/year  1-2 planets/year.

  37. As opposed to high-mag (central caustic) events, Low-magnification (planetary caustic) events: Lower planet detection efficiency, but much more common: Potential for tens of microlensing planets/year. A. Cassan

  38. Beaulieu et al. 2006

  39. Need network of 1-2m class telescopes with degree-scale imagers for continuous monitoring of many low-mag events in search of planetary perturbations: “Generation II microlensing”

  40. Since 2011: A generation-II microlensing experiment: Wise Obs., Israel, D=1m, 1 deg2 Yossi Shvartzvald is there OGLE IV, Chile, D=1.3m, 1.4 deg2 MOA-II, NZ, D=1.8m, 2.3 deg2

  41. The generation-II network

  42. The generation-II network

  43. The generation-II network

  44. The generation-II network

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