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Planet hunting through gravitational m icrolensing

Planet hunting through gravitational m icrolensing. Shude Mao. Collaborators: Yingyi Song, Wei Zhu, Matthew Penny, Andy Gould, Doug Lin. 25/09/2013 @ Tsinghua. Outline. Basics of microlensing Current status Discovery of extrasolar planets Multiple planets and degeneracy

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Planet hunting through gravitational m icrolensing

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  1. Planet hunting through gravitational microlensing Shude Mao Collaborators: Yingyi Song, Wei Zhu, Matthew Penny, Andy Gould, Doug Lin 25/09/2013@ Tsinghua

  2. Outline • Basics of microlensing • Current status • Discovery of extrasolar planets • Multiple planets and degeneracy • Future directions

  3. What is near-field microlensing? Standard light curve is (Paczynski 1986) symmetric, achromatic & non-repeating Image credit: NASA/ESA Image separation is too small to resolve individual images, we can only observe magnification effects.

  4. Basic scales in microlensing Einstein Ring lens DS source • Einstein radius rE~ M1/2，~few AU, coincident with the size of the solar system! • Einstein radius crossing time tE~rE/V, degeneracy! • Angular size ~ mas (difficult to resolve)!

  5. Where are we looking? Mostly here here Small Magellanic Cloud Galactic bulge and here Current surveys monitor the brightness of order ~ several hundred million stars nightly and in real time since 1990’s. Large Magellanic Cloud PHYS40691 - FRONTIERS OF ASTROPHYSICS: Gravitational Microlensing in Galaxies NOAO/AURA/NSF Image/EamonnKerins

  6. What do we see? Credit: OGLE Challenges: probability~10-6, event rate ~ 10 events per year per 106 stars.

  7. Examples: a high magnification standard light curve tE~42 days, typical max ~3000 fs=0.04 Obs. max ~36 OGLE-2004-BLG-343

  8. Examples: A short standard event： tE=1.25 day, Free-floating planets? Statistically! 8 years of data OGLE-2008-BLG-365

  9. Black hole microlensing candidate 4 years OGLE-1999-BUL-32 • Subtle parallax signature • duration~ 640 days; longest event ever (Mao et al. 2003) • M~fewMsun, and dark - a stellar mass black hole? • Several other BH candidates have been proposed

  10. Microlensing data sets: Two decades of observations by OGLE, MOA, MACHO etc. assembled time series for hundreds of millions of stars toward GC, LMC, SMC, etc. To date ~ 12,000 events have been detected The vast majority of events are detected towards the Galactic bulge Duration: a few hours to 4 years, peak magnification: 1to ~few thousand Current event rate by OGLE ~2000/yr, real-time

  11. Microlensing applications • Dark matter: MACHOS? • Galactic structure/dynamics • Color-magnitude diagrams • Microlensing optical depth maps • Proper motions (kinematics) • Extinction maps • High magnification events/caustic crossing events • Stellar atmosphere (limb-darkening) • metallicity, surface gravity of stars • Black holes? • Extrasolar planets Reference image, R Target image, T

  12. Principles of extrasolar planet detection with microlensing Einstein Ring lens DS source • Einstein radius rE~ M1/2，few AU, coincident with the size of the solar system! • Einstein radius crossing time tE~rE/V, degeneracy! • Angular size ~ mas (difficult to resolve)!

  13. Principle of planet detection Positive parity source Negative parity lens • The presence of the planet perturbs the image positions and magnifications • In fact it can create one or three extra images!

  14. Microlensing planet: OGLE-2005-BLG-390 (Beaulieu et al 2006) Principle was discussed in Mao & Paczynski (1991) and Gould & Loeb (1992)

  15. Beaulieu et al 2006 Bond et al 2004 Udalski et al 2005; Dong et al 2009 Family Album of Microlensing Planets ~5.5 MEarth Apeak ~ 3 ~830 MEarth Apeak ~ 8 Apeak ~ 40 ~1200 MEarth Sumi et al. 2010 Batista et al., 2011 Gould et al 2006 ~22 MEarth ~1000 MEarth Apeak ~ 12 Apeak ~ 14 ~13 MEarth Apeak~ 800 Muraki et al., 2011 Gaudi et al 2008 Dong et al in prep Apeak ~ 500 ~14 MEarth Apeak~ 8 ~86 MEarth Apeak ~ 290 ~50 MEarth

  16. Exoplanet discovery space • Between 0.5-10 AU - 17% have Jupiters, 50% Neptune and Super-Earths Cassanet al. (2012); Gould (2006, 2010) • Free-floating planets may be common: ~ 1.8 per star • Sumi et al. (2011), Nature RV microlensing kepler (Mao 2012)

  17. Testing core accretion theories • Microlensing can be particularly useful for testing the core accretion planet formation theory. Ida & Lin (2008, 2010)

  18. Simulated planetary events Zhu, Mao et al. (2013) Jupiter • Microlensing detection efficiency: • 3% show planetary signatures, of which 8% show multiple planets! (cf. radial velocity and transit ~30%) • However, with planetary events in high proportions in high magnification events! Saturn Earth semi-major axis (AU) Separation/rE

  19. First: OGLE-2006-BLG-019L A Saturn and Jupiter analog! Gaudi et al. (2008) • q1 = 1.35 × 10-3, d1~2.3 AU • q2 = 4.86 × 10-4, d2 ~ 4.6 AU

  20. Second: OGLE-2012-BLG-0026 Han et al. (2013) • q1 = (1.30 ± 0.01) × 10-4, d1 = 1.034 ± 0.001 • q2 = (7.84 ± 0.21) × 10-4, d2 = 1.304 ± 0.006 • tE = 93.92 ± 0.58 days Close/wide degeneracy!

  21. OGLE-2005-BLG-071 Binarymodel: • q = (7.1 ± 0.3) × 10-3 • d = 1.294 ± 0.002 • tE = 70.9 ± 3.3 days • residuals? ？？？ Udalskiet al. (2005)

  22. OGLE-2005-BLG-071 Wide+ of MCMC A: • q = (7.5 ± 0.2) × 10-3 • d~1.306 • tE~ 71.1 +2.3/-2.4 days • With orbital motion and parallax! • Other perturbations? Dong et al. (2008)

  23. double-lens to triple-lens degeneracy • q1 = 2.49 × 10-3, d1 = 1.303, q2 = 4.99 × 10-3, d2 = 1.304 • φ= 3 degree (a range is allowed)! Song, Mao & An (2013)

  24. double-lens/triple-lens degeneracy • Double and triple lenses can be shown to be mathematically degenerate to second order • If unaccounted for, it may bias the multiple fraction to be lower than the true value • We give detailed recipes how this degeneracy can be explored Song, Mao & An (2013)

  25. Current mode of discovery Current mode of discovery: Survey (MOA and OGLE collaborations) + follow-up (microFun/PLANET collaborations) around the globe MicroFun - 24 hour relay

  26. Future • Near-future • Survey much areas of sky, more fields (OGLE-IV: 233 fields, 330 square degrees) • Part-time pure survey mode • Microlensing in five years • KMTnet: pure survey mode • Microlensing in ten years? • Space satellites (Euclid/WFIRST)

  27. Microlensing in ~5 years • KMTNet • Three 1.6m telescope with ~4 deg2 FoV • Thousands of events with ~15min cadence per year • will find ~40 ηEarth and 1-2 orders of mag more Neptunes and Jupiters in a 5-yr survey South Africa Chile Australia

  28. Microlensing in ~10 years (?) OGLE image Hubble ACS HRC • Space allows to observe in IR, and study fainter, smaller stars to discover very low-mass planets • Can partially/completely remove the degeneracies

  29. Microlensing from space: Euclid A simulated event at baseline and peak 0.1/pixel 0.3/pixel baseline peak Euclid (2020) focus on weak lensing and BAO, but may have a microlensing component

  30. A simulated Earth-mass event Deviation around 6 hours; can be discovered in space.

  31. Sensitivities and yields 5 year mission, two-month per year • Default MF: 1/3 per log m per log a, flat log mass dependence • total detections (-1.5<log M/Me<3): ~400, 6 Earths (range: 6-100 in different models) • Sensitivity to free floating planets Kepler

  32. Summary • Microlensing has diverse applications • Current real-time event rate to ~2000 events/yr • More subtle effects can be seen • Multiple planets; there is some degeneracy in modelling; triple lensing remains a challenge! • Exoplanet microlensing will remain exciting from the ground (and space!) in the next decade! • Will complement other methods and test planet formation theory • Chinese contribution from Dome-A?

  33. Exotic microlensing events parallax finite source size binary lens OGLE-1999-BUL-19 Smith, Mao et al. (2002) EROS-BLG-2000-5 An et al (2002) Alcock et al. (1997) • Standard light curve assumes single lens and point source with linear motions! • Extra features in the light curve give additional constraints to break the microlensdegeneracy

  34. Parameters of triple lens system

  35. Degeneracies in triple gravitational microlensing

  36. The double-triple lens degeneracy

  37. Euclid's sensitivity Expected yields for different assumed mass functions Total detections (-1.5<log(M/Me)<3): Default: 390 RV: 307 uL: 438 uL saturated: 267 Expected measurement of planet mass fn Mp-a plane sensitivity Penny et al., MNRAS, 2012. In prep.

  38. Exoplanet discovery space From space Microlensing proving to be best for planets like those in our Solar system!

  39. Every Image is like HST! OGLE image with 0.5” seeing Hubble ACS HRC

  40. Microlensing as a Nature telescope EROS-2004-BLG-254 shows strong broadening of magnification peak due to finite source smearing UVES spectra of source obtained whilst still being microlensed indicated source is a K3 III Bulge 10.5 kpc away Lens angular Einstein radius θE = 0.114 mas determined from light-curve modeling and from V, V-I photometry of source Lens proper motion relative to source given by μ = θE/tE = 3.1 mas/yr Can be used to obtain limb-darkening profiles. (Cassan et al 2006)

  41. Orbital motion in microlensing events

  42. Extinction maps Baade Window: l=1b=-3.9 l=0b=-2 • Observed red clump giants are redder and fainter than expected due to extinction (Stanek et al. 1997, Sumi 2004)! • We can use to obtain maps of extinction; many anomalous in reference to the standard extinction law!

  43. Limb darkening profile Limb-darkened stellar disk intensity profile is: where parameter a is a parameter computed from stellar atmosphere models Table from Cassan et al (2006) Finite source events observed to date are proving a stern test of stellar atmosphere models for ~10 events observed so far!

  44. Essential numbers • Lens mass degeneracy! • Partial or complete removal possible with exotic events (parallax, finite source size).

  45. Statistical measures of microlensing • Optical depth • independent of the mass function of lenses •  can be used to infer the overall mass distribution of our Galaxy • Event rate and duration distribution • Event rate ~10 events/million stars/year, very low! • The analysis of event time scale distribution offers a method to determine the lens mass function, independent of light.

  46. Effects of rotation Can cause caustics to change shape Or to rotate ~5% predicted ~20% observed Selection effects? Penny, Mao & Kerins (2011)

  47. 1. Distribution of all planets; • 2. Distribution of detected planets; • 3. Microlensing detection efficiency: •     All planetary events/all microlensing events = 155/5000; •     Multiple-planetary events/all planetary events = 12/155; • 4. Distribution of impact parameters. • Best wishes, • Wei

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