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

Conceived problems with microlensing: 1.Seems complicated… 2.and hence results suspect… 3.No “follow up” of planets possible 4. Statistically useless due to haphazard survey strategies 5. Planet yield so small -- not worth trouble?

 R

 R  S D LS D OL D OS EE

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

 R  S D LS D OL D OS EE

 R      S  D LS D OL D OS I + S + SA = I + A

~milliarcsec

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

  D OL / v ~ M 1/2 Einstein-ring crossing timescale: For  D OL =8 kpc,  v=20 km/s   (1M sun ) = 2 months   (1M J )=2 days S. Gaudi

The first microlensing lightcurves (LMC) Alcock et al. 

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

Bond et al. 2004

Beaulieu et al. 2006

Udalski et al. 2005

Gould et al. 2006

“Jupiter”+”Saturn” system: =“Saturn”, 4=“Jupiter” Gaudi et al. 2008

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

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

Simulation by S. Gaudi

q = M p / M host

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)

Caustic cusps

Magnification still ~ 1/(distance to caustic)

A. Cassan 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.

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

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

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

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

Udalski et al Gould et al Gaudi et al. 2008

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

1 st Generation microlensing

~ 650 events/year

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

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.

A. Cassan 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.

Beaulieu et al. 2006

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”

Since 2011: A generation-II microlensing experiment: Wise Obs., Israel, D=1m, 1 deg 2 OGLE IV, Chile, D=1.3m, 1.4 deg 2 MOA-II, NZ, D=1.8m, 2.3 deg 2  Yossi Shvartzvald is there

The generation-II network

Group OGLE

The generation-II network Group OGLE MOA

The generation-II network Group OGLE MOA WISE

Gen II 8 deg 2 of bulge with highest lensing rate covered quasi- continuously by all 3 telescopes, cadences min

2011 season: some typical low-mag event light curves (no anomalies) :

2011 Generation-II planetary events: MOA-293 I-band (mag) HJD Yee, Shvartzvald et al Survey data only: OGLEMOAWise All data:

OGLEMOAWise 2011 Generation-II planetary events

What to expect from Generation II? a simulation: Monte-Carlo of many Solar- System-like planetary systems, host star properties matching those of bulge microlensing population, random inclinations. Shvartzvald & Maoz 2012

Various scalings of orbital radius with host mass Shvartzvald & Maoz 2012

Ray trace through systems…… …add real sampling sequences, photometry errors… …search for planetary-type anomalies with same detection criteria as real data

Shvartzvald & Maoz 2012 Simulation results: can detect ~10-20% of planets around microlensed stars; ~100 stars in Gen-II footprint, so (10 to 20)*f planets per season.

Planet identity

Conceived problems with microlensing: 1.Seems complicated… but calculable. An elegant geometric method. 2. Light curve complexity  uniqueness of models 3. No “follow up” possible Not quite valid/true. 4. Planet yield so small -- not worth trouble? Untrue! Unique probe of normal planetary systems near snow line, beyond Solar neighborhood, free-floating planets, yield growing thx to Generation II (plus controlled experiment)

Some calendar numerology: Today, 18 Dec 2012 is: 12 / 2 days since (just married?); 3 days until (end of the world); 24,377 days since May 2, 1946 = century Happy 2/3 centennial Birthday, Tsevi !!

Planet identity