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

ë = c2R4GM (ü 1)

R

S

DLS DOL

DOS

ë = c2R4GM (ü 1)

E

“microlensing”

(in our Galaxy):

In distant galaxies:

“macrolensing”,

“galaxy lensing”:

cluster lensing:

òE ù 1 asec

òE ù 10 asec

òE = 10à 6 asec

R

S

DLS DOL

DOS

ë = c2R4GM (ü 1)

E

R

S

DLS DOL

DOS

I+S + SA = I+A

ë = c2R4GM (ü 1)

~milliarcsec

Magnification=image area / source area :

magnification ~ 1/ (impact parameter)

DOL / v ~ M1/2

Einstein-ring crossing timescale:

ForDOL=8 kpc,

v=20 km/s

(1Msun) = 2 months

(1MJ)=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: 1+2+3+5=“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 = 0.50

0.50 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: 0.7MJ (4.6 AU) and 0.1MJ (3.8 AU)

Simulation by S. Gaudi

Simulation by S. Gaudi

Simulation by S. Gaudi

q = Mp / Mhost

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.

SLensR M

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?

“1st Generation” survey strategy (Gould & Loeb 1992) focused on bright, high-magnification (mag>100) events.

To date, only ~20 microlensing planets.

Udalski et al. 2005

Gould et al. 2006

Gaudi et al. 2008

1st Generation microlensing

OGLE, Chile, 1.3m MOA, NZ, 1.8m

• low cadence (~ once a night)

1st Generation microlensing

1st Generation microlensing

~650 events/year ~650 events/year

1st 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 deg2

OGLE IV, Chile, D=1.3m, 1.4 deg2 MOA-II, NZ, D=1.8m, 2.3 deg2

Yossi Shvartzvald is there

The generation-II network

The generation-II network

Group

OGLE

The generation-II network

Group

OGLE

MOA

The generation-II network

Group

OGLE

MOA

WISE

Gen II8 deg2 of bulge with highest lensing rate covered quasi-continuously by all 3 telescopes, cadences 20-40 min

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

2011 Generation-II planetary events:

MOA-293

I-ba

nd (

mag

)I-

band

(m

ag)

I-ba

nd (

mag

)I-

band

(m

ag)

HJD-2450000HJD-2450000

Yee, Shvartzvald et al. 2012

Survey Survey data only:data only:

OGLEOGLEMOAMOAWiseWise

All data:All data:

OGLEOGLEMOAMOAWiseWise

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

SLensR M

Shvartzvald & Maoz 2012

S

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

S

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.

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 12.12.12 (just married?);

3 days until 21.12.12 (end of the world);

24,377 days since May 2, 1946

=0.66667 century

Happy 2/3 centennial Birthday, Tsevi !!