Microlensing Working Group Review David Bennett (Notre Dame) MicroFUN Microlensing Follow-Up Network

Features of Microlensing General consensus on forward directions. –Exoplanet Forum + Pale Blue Dot Reviews Two (and only two) paths forward –Both Recommended by ExoPTF –Ground based 1.5-2m wide-FOV telescope network 1-5 years, ~$20M Now funded: Korea Microlensing Telescope Network (KMTNet) Frequency of planets  1 M  beyond the snow line. –Space based, 5-10 years, ~$300M + Launch Complete census of planets with mass greater than Mars and a  0.5 AU, including habitable planets. Possible joint Exoplanet + Dark Energy mission

The near-term: automated follow-up The near-term: automated follow-up 1-5 yr Milestones: A.An optimised planetary microlens follow-up network, including feedback from fully-automated real-time modelling. B.The first census of the cold planet population, involving planets of Neptune to super-Earth (few M ⊕ to 20 M ⊕ ) with host star separations 2-3 AU. C.Under highly favourable conditions, sensitivity to planets close to Earth mass with host separations around 2 AU. Running existing facilities with existing operations

The medium-term: wide-field telescope networks The medium-term: wide-field telescope networks 5-10 yr Milestones: A.Complete census of the cold planet population down to ~10 M ⊕ with host separations above 1.5 AU. B.The first census of the free-floating planet population. C.Sensitivity to planets close to Earth mass with host separations around 2 AU. Several existing nodes already (MOA-II, OGLE-IV). Korean Microlensing Telescopes NETwork (Park, Han et al.) funded !

The longer-term: a space-based microlensing survey ~10 yr Milestones: A.A complete census of planets down to Earth mass with separations exceeding 1 AU B.Complementary coverage to Kepler of the planet discovery space. C.Potential sensitivity to planets down to 0.1 M ⊕, including all Solar System analogues except for Mercury. D.Complete lens solutions for most planet events, allowing direct measurements of the planet and host masses, projected separation and distance from the observer. Dedicated ~400 M$, or participation to Dark energy probes Excellent synergy Dark Energy/Microlensing

Microlensing Discoveries vs. Other Techniques Microlensing discoveries in red Doppler discoveries in black Transit discoveries shown as blue squares Direct detection, timing and astrometry are magenta, green, and orange triangles Microlensing opens a new window on exoplanets at 1-5 AU Sensitivity approaching 1 Earth-mass Most planets here!

Ground-based µlensing surveys probe planets with M  1 M  beyond the snow-line. A space-based survey will provide a complete census of planetary systems with mass greater than Mars and a  0.5 AU (from 0 to  with Kepler), including habitable planets.

Planet mass vs. semi-major axis/snow-line “snow-line” defined to be 2.7 AU (M/M  ) since L  M 2 during planet formation Microlensing discoveries in red. Doppler discoveries in black Transit discoveries shown as blue circles Super-Earth planets beyond the snow-line appear to be the most common type yet discovered MOA-192

The Physics of Microlensing Foreground “lens” star + planet bend light of “source” star Multiple distorted images –Only total brightness change is observable Sensitive to planetary mass Low mass planet signals are rare – not weak Stellar lensing probability ~a few  –Planetary lensing probability ~ depending on event details Peak sensitivity is at 2-3 AU: the Einstein ring radius, R E Einstein’s telescope

Microlensing Target Fields are in the Galactic Bulge 10s of millions of stars in the Galactic bulge in order to detect planetary companions to stars in the Galactic disk and bulge. 1-7 kpc from Sun Galactic centerSun 8 kpc Light curve Source star and images Lens star and planet Telescope

A planet can be discovered when one of the lensed images approaches its projected position. Must monitor many events continuously so that planetary signals are not missed. Lensed images at  arcsec resolution View from telescope

Magnification Determined by Caustics Deviation from single-lens is largely determined by “caustics”. Multiple planet sensitivity in high magnification events. Planetary caustic Lower magnification Larger area Central caustic High magnification Host star (lens) Planet (lens) No planet detection Detection via central caustic Detection via planetary caustic

How Low Can We Go? Limited by Source Size Mars -mass planets detectable if solar-type sources can be monitored! (Bennett & Rhie 1996) angular Einstein radius angular source star radius For  E   * : low-mass planet signals are rare and brief, but not weak

NextGen  Lensing Survey For significant sensitivity increase over current Alert & Follow-up effort Requirements to detect ~3 (cold) Earth-mass planets per year: –Continuous monitoring of all ~800 microlensing events detected per year –Monitor ~16 square degrees of the Galactic bulge continuously with ~10 minute sampling using 1-2m class telescopes, distributed longitudinally throughout the southern hemisphere. –Large FOV (2-4 square degree) cameras needed.

Microlensing Telescope Locations MOA OGLE PLANET Network Survey Telescopes CTIO  FUN Network High Magnification Alert!! KMTNet

Hardware Funded Internationally MOA-II (NZ, currently operating) –1.8m telescope, 2.18 sq. degree camera –MOA-III upgrade to 10 sq. degree camera proposed OGLE -IV (Chile, 2009) –1.3m telescope, upgrade to 1.4 sq. degree camera KMTNet (South Africa, Chile, Australia) –1.6m telescopes, 4 sq. degree cameras –Funded in Dec., 2008 ExoPTF: “Recommendation A. II. 1 Increase dramatically the efficiency of a ground-based microlensing network by adding a single 2 meter telescope.”

Lens System Properties Einstein radius :  E =  * t E /t * and projected Einstein radius, –  * = the angular radius of the star – from the microlensing parallax effect (due to Earth’s orbital motion).

If only  E or is measured, then we have a mass-distance relation. Such a relation can be solved if we detect the lens star and use a mass-luminosity relation –This requires HST or ground-based adaptive optics With  E,, and lens star brightness, we have more constraints than parameters Finite Source Effects & Microlensing Parallax Yield Lens System Mass mass-distance relations: Space-based parallaxes using Solar System Science Spacecraft?

Double-Planet Event: OGLE-2006-BLG distinct planetary light curve features OGLE alerted 1 st feature as potential planetary signal High magnification Feature #4 requires an additional planet Planetary signals visible for 11 days Features #1 & #5 require the orbital motion of the Saturn- mass planet  FUN, OGLE, MOA & PLANET OGLE alert

OGLE-2006-BLG-109 Light Curve Detail OGLE alert on feature #1 as a potential planetary feature  FUN (Gaudi) obtained a model approximately predicting features #3 & #5 prior to the peak But feature #4 was not predicted - because it is due to the Jupiter - not the Saturn Gaudi et al (2008) published in Science

OGLE-2006-BLG-109 Light Curve Features The basic 2-planet nature of the event was identified during the event, But the final model required inclusion of orbital motion, microlensing parallax and computational improvements (by Bennett).

OGLE-2006-BLG-109Lb,c Caustics Curved source trajectory due to Earth’s orbital motion Feature due to Jupiter Planetary orbit changes the caustic curve - plotted at 3-day intervals

OGLE-2006-BLG-109 Source Star The model indicates that the source is much fainter than the apparent star at the position of the source. Could the brighter star be the lens star? source from model Apparent source In image

OGLE-2006-BLG-109Lb,c Host Star OGLE images show that the source is offset from the bright star by 350 mas B. Macintosh: Keck AO images resolve lens+source stars from the brighter star. But, source+lens blend is 6  brighter than the source (from CTIO H-band light curve), so the lens star is 5  brighter than source. –H-band observations of the light curve are critical because the lens and source and not resolved Planet host (lens) star magnitude H  –JHK observations will help to constrain the extinction toward the lens star

Implications of Light Curve Model Apply lens brightness constraint: H L  Correcting for extinction: H L0 =  0.25 –Extinction correction is based on H L -K L color –Error bar includes both extinction and photometric uncertainties Lens system distance: D L = 1.54  0.13 kpc Other parameter values: “Jupiter” mass: m b = 0.73  0.06 M Jup semi-major axis: “Saturn” mass: m c = 0.27  0.03 M Jup = 0.90 M Sat semi-major axis: “Saturn” orbital velocity v t = 9.5  0.5 km/sec eccentricity inclination i = 63  6 

Orbital Motion Modeling 4 orbital parameters are well determined from the light curve –2-d positions and velocities –Slight dependence on distance to the source star when converting to physical from Einstein Radii units Masses of the host star and planets are determined directly from the light curve –So a full orbit is described by 6 parameters (3 relative positions & 3 relative velocities) –A circular orbit is described by 5 parameters Models assume planetary circular motion –2-d positions and velocities are well determined –Orbital period is constrained, but not fixed by the light curve –The orbital period parameter can be interpreted as acceleration or 3-d Star-Saturn distance (via a = GM/r 2 ) Details in Bennett et al (2009) in preparation

Full Orbit Determination for OGLE-2006-BLG-109Lc Series of fits with fixed orbital acceleration (weight with fit  2 ) Each fit corresponds to a 1- parameter family of orbits parameterized by v z –unless Assume the Jupiter orbits in the same plane and reject solutions crossing the Jupiter orbit or that are Hill-unstable Weight by prior probability of orbital parameters –planet is unlikely to be near periastron if   0 Families of solutions corresponding to best models at various values of a.

Full calculation using Markov chains run at fixed a. Include only Hill-stable orbits results: Full Orbit Determination for OGLE-2006-BLG-109Lc RV follow-up w/ 40m telescope –K = 13 km/sec (H = 17.2)

Current Event: MOA-2009-BLG-266 Planet discovered by MOA on Sept. 11, 2009 Low-mass planet –Probably Hope to get mass measurement from Deep Impact (now EPOXI) Spacecraft

Space-Based Microlensing Parallax 2004: study LMC microlensing w/ DI imaging (proposed) 2009: Geometric exoplanet and host star mass measurements with DI

What can we expect from Space? Example: Microlensing Planet Finder (Bennett PI) Simulations from Bennett & Rhie (2002) Basic results confirmed by independent simulations Continuous observations of 4  0.66 sq. deg. central Galactic bulge fields: ~2  10 8 stars Observations in near IR to increase sensitivity ~15,000 events in 4 seasons

Ground-based confusion, space-based resolution Space-based imaging needed for high precision photometry of main sequence source stars (at low magnification) and lens star detection High Resolution + large field + 24hr duty cycle => Microlensing Planet Finder (MPF) Space observations needed for sensitivity at a range of separations and mass determinations CTIOHST MPF

Lens Star Identification from Space Lens-source proper motion gives  E =  rel t E  rel = 8.4  0.6 mas/yr for OGLE-2005-BLG-169 Simulated HST ACS/HRC F814W (I-band) single orbit image “stacks” taken 2.4 years after peak magnification –2  native resolution –also detectable with HST WFPC2/PC & NICMOS/NIC1 Stable HST PSF allows clear detection of PSF elongation signal A main sequence lens of any mass is easily detected (for this event) M L = 0.08 M  M L = 0.35 M  M L = 0.63 M  raw imagePSF subtracted binned Simulated HST images:

The Microlensing Planet Finder (MPF) David Bennett, PI Ed Cheng, Deputy PI NASA/GSFC Management Lockheed Martin, prime contractor

Space vs. Ground Sensitivity space ground Habitable Earths orbiting G & K stars accessible only from space Expect 60 free- floating Earths if there is 1 such planet per star

MPF Complements Kepler Figures from B. MacIntosh of the ExoPlanet Task Force

MPF Complements Kepler Figures from B. MacIntosh of the ExoPlanet Task Force

Planet TypeqDiscoveries Earth/Venus/Mars  Jupiter Saturn 3  Uranus/Neptune 5  MPF’s Predicted Discoveries Expected MPF planet detections if each lens system has a “solar system analog” planetary system with the same star-planet separations and mass ratios as our own planetary system. The number of expected MPF planet discoveries as a function of planet mass.

“What’s the best way to take the census of every kind of planet orbiting every kind of star? It’s not by looking for wobbles in stars’ radial (line-of- sight) velocities, the method that has turned up nearly all of the 220 giant exoplanets discovered since Instead, it would be by using a space telescope to search for large numbers of microlensing events — temporary brightenings caused by the slight gravitational focusing of starlight when a massive object passes between us and a background star.” MPF! From Sky & Telescope, July 2007 issue:

“Recommendation B. II. 2 Without impacting the launch schedule of the astrometric mission cited above, launch a Discovery-class space-based microlensing mission to determine the statistics of planetary mass and the separation of planets from their host stars as a function of stellar type and location in the galaxy, and to derive   over a very large sample. From the ExoPlanet Task Force:

Simulated Planetary Light Curves Exposures every minutes Strong signals Unambiguous information Moons detectable! (1.6 lunar masses) Bennett & Rhie (2002)

Comparison to Simulations Simulations by Ida & Lin with different parameters yield very different exoplanet distributions. In all cases, MPF detects most types of exoplanets. Without MPF, we can only detect planets in the tails of the distribution.

Lens Detection Provides Accurate Mass Estimate Lens will be detected for the majority of main-sequence lenses. Host star masses will be measured to 10% for half of the events. Projected separations will be measured to 5% for half of the events.

MPF Mission Design 1.1-m aperture consisting of a three- mirror anastigmat telescope feeding a 147 Mpixel HgCdTe focal plane ( arrays) The spacecraft bus is a near-identical copy of that used for Spitzer. The telescope system very similar to NextView commercial Earth- observing telescope designs. Detectors developed for JWST meet MPFs requirements. All elements are at TRL 6 or better. Total Cost $300 (without launch vehicle) MPF Mission Requirements

Dark Energy Synergy Space-based microlensing mission telescope requirements are very similar to the requirements for many proposed dark energy missions. Combined dark energy/planet finding mission probably could be accomplished at a substantial savings. JDEM, DUNE/SPACE/Euclid –Wide FOV, >1.1m aperture, technical specifications appear to satisfy space-based microlensing survey specifications –DUNE/SPACE/Euclid can meet all the science goals without modification to hardware. Trade study: –Observing time –Pass bands –FOV and Detectors –Orbit –Telemetry –Aperture –Optics –Pointing

Summary Ground-based Next-Generation Survey : ~ $ 30M –Hardware funded by Japan, Poland, and Korea –Frequency of planets  1 M  beyond the snow line. –Test planet formation theories. Either: Space-based Microlensing Mission: +$300M + launch –Complete census of planets with mass greater than Mars and a  0.5 AU. –Sensitivity to all Solar System planet analogs except Mercury. –Demographics of planetary systems - tests planet formation theories. –Detect “outer” habitable zone (Mars-like orbits) where detection by imaging is easiest. –Can find moons and free floating planets. Or: Joint  lensing/Dark Energy Mission +$100M—$200M? –see Beaulieu’s talk Total cost to “Exoplanet Community”: $105M(?)—$405M

Microlensing Strengths Peak sensitivity beyond the snow line. – K Sensitivity down to very low-mass planets. –Mass greater than that of ~10% Mars. Sensitivity to long-period and free-floating planets. –0.5 AU -  Sensitivity to planets over a wide range of host masses. –M < M  Sensitivity to planets throughout the Galaxy. –1-8 kpc Sensitivity to multiple-planet systems.

Commonly heard complaints… But you don’t know anything about the star, orbits, etc! — Typically can measure host star and planet masses to ~10-20%. — In some special cases can learn something about the orbit. But the systems are so far away and faint! — Sufficiently bright to measure flux, color, and in some cases get spectra. But you only see it once! — Signals are large and unambiguous. — Demographics of planetary systems.