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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 - PowerPoint PPT Presentation
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Planet hunting through
gravitational microlensingShude Mao
25/09/2013 @ Tsinghua
Collaborators: Yingyi Song, Wei Zhu, Matthew Penny,
Andy Gould, Doug Lin
Outline• Basics of microlensing• Current status• Discovery of extrasolar
planets• Multiple planets and
degeneracy• Future directions
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.
DS lens source
Basic scales in microlensing
• 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)!
Einstein Ring
PHYS40691 - FRONTIERS OF ASTROPHYSICS:Gravitational Microlensing in GalaxiesNOAO/AURA/NSF Image/Eamonn Kerins
Mostly herehereand here
Galactic bulge
SmallMagellanicCloud
LargeMagellanicCloud
Current surveys monitor the brightness of order ~ several hundred million stars nightly and in real time since 1990’s.
Where are we looking?
What do we see?
Credit: OGLEChallenges: probability~10-6, event
rate ~ 10 events per year per 106
stars.
Examples: a high magnification standard light curve
tE~42 days, typicalmax ~3000fs=0.04
Obs. max ~36
OGLE-2004-BLG-343
Examples: A short standard event:
tE=1.25 day,Free-floating planets? Statistically!
8 years of data
OGLE-2008-BLG-365
Black hole microlensing candidate
• M~few Msun, and dark - a stellar mass black hole?
• Several other BH candidates have been proposed
(Mao et al. 2003)
4 years
OGLE-1999-BUL-32 • Subtle parallax
signature • duration~ 640
days; longest event ever
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: 1 to ~few thousand
– Current event rate by OGLE ~2000/yr, real-time
Microlensing applications
Reference image, R Target image, T
• 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
DS lens source
Principles of extrasolar planet detection with
microlensing
• 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)!
Einstein Ring
lens
source
• The presence of the planet perturbs the image positions and magnifications
• In fact it can create one or three extra images!
Negative parity
Positive parity
Principle of planet detection
Microlensing planet: OGLE-2005-BLG-390
(Beaulieu et al 2006)
Principle was discussed in Mao & Paczynski (1991) and Gould & Loeb (1992)
Family Album of Microlensing Planets
~5.5 MEarth Apeak ~ 3
~14 MEarth Apeak~ 8
~22 MEarth Apeak ~ 12
Apeak ~ 8~830 MEarth
Apeak ~ 290~86 MEarth
~1000 MEarth Apeak ~ 14
Beaulieu et al 2006
Sumi et al. 2010
Bond et al 2004
Gaudi et al 2008 Muraki et al., 2011
Batista et al., 2011
~1200 MEarthApeak ~ 40
Udalski et al 2005; Dong et al 2009
~13 MEarth Apeak ~ 800
Gould et al 2006
Apeak ~ 500~50 MEarth
Dong et al in prep
Exoplanet discovery space
(Mao 2012)
• Between 0.5-10 AU - 17% have Jupiters, 50% Neptune and Super-Earths Cassan et al. (2012); Gould (2006, 2010)
• Free-floating planets may be common: ~ 1.8 per star
Sumi et al. (2011), Nature
keplermicrolensing
RV
Testing core accretion theories
• Microlensing can be particularly useful for testing the core accretion planet formation theory.
Ida & Lin (2008, 2010)
Simulated planetary events
• 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!
Zhu, Mao et al. (2013)
Earth
Saturn
Jupiter
Separation/rE
semi-major axis (AU)
First: OGLE-2006-BLG-019L
• q1 = 1.35 × 10-3, d1 ~2.3 AU • q2 = 4.86 × 10-4, d2 ~ 4.6 AU
A Saturn and Jupiter analog!
Gaudi et al. (2008)
Second: OGLE-2012-BLG-0026
• 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!
Han et al. (2013)
OGLE-2005-BLG-071Binary model:• q = (7.1 ± 0.3)
× 10-3
• d = 1.294 ± 0.002
• tE = 70.9 ± 3.3 days
residuals?Udalski et al. (2005)
???
OGLE-2005-BLG-071Wide+ 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)
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)
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)
Current mode of discoveryCurrent mode of discovery:
Survey (MOA and OGLE collaborations) + follow-up (microFun/PLANET collaborations) around the globe
MicroFun - 24 hour relay
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)
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
Chile
South Africa
Australia
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
Microlensing from space: Euclid
A simulated event at baseline and peak
baseline
peak
0.3/pixel 0.1/pixel
Euclid (2020) focus on weak lensing and BAO, but may have a microlensing component
A simulated Earth-mass event
Deviation around 6 hours; can be discovered in space.
Sensitivities and yields
• 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
5 year mission,
two-month per year
Kepler
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?
Exotic microlensing events
EROS-BLG-2000-5An et al (2002)
OGLE-1999-BUL-19
Smith, Mao 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 microlens degeneracy
parallax finite source size
binary lens
Parameters of triple lens system
Degeneracies in triple gravitational microlensing
The double-triple lens degeneracy
Euclid's sensitivityTotal detections (-1.5<log(M/Me)<3): Default: 390 RV: 307 uL: 438 uL saturated: 267
Expected yields for different assumed mass functions
Expected measurement of planet mass fn
Mp-a plane sensitivity
Penny et al., MNRAS, 2012. In prep.
Exoplanet discovery space
Microlensing proving to be best for planets like those in our Solar system!
From space
Every Image is like HST!
OGLE image with 0.5” seeing
Hubble ACS HRC
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)
Orbital motion in microlensing events
Extinction maps
• 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!
l=0b=-2
Baade Window: l=1b=-3.9
Limb darkening profile
Finite source events observed to date are proving a stern test ofstellar atmosphere models for ~10 events observed so far!
Limb-darkened stellar disk intensity profile is:
where parameter a is a parameter computed from stellar atmosphere models
Table from Cassan et al (2006)
Essential numbers
• Lens mass degeneracy! • Partial or complete removal
possible with exotic events (parallax, finite source size).
• 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.
Statistical measures of microlensing
Effects of rotationCan cause caustics to change shape
Or to rotate
~5% predicted~20% observed
Selection effects?
Penny, Mao & Kerins (2011)
• 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
First: OGLE-2006-BLG-019L(Gaudi et al. 2008)
• q1 = 1.35 × 10^-3, d1 = 2.3 AU = 1.04• q2 = 4.86 × 10^-4, d2 = 4.6 AU = 2.07
Second: OGLE-2012-BLG-0026(Han et al. 2013)
Second: OGLE-2012-BLG-0026(Han et al. 2013)
Second: OGLE-2012-BLG-0026(Han et al. 2013)
Model D:• 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
OGLE-2005-BLG-071 (Udalski et al. 2005)
Wide model:• q = (7.1 ±
0.3) × 10^-3• d = 1.294 ±
0.002• tE = 70.9 ±
3.3 days
OGLE-2005-BLG-071 (Dong et al. 2008)
Wide+ of MCMC A:
• q = (7.5 ± 0.2) × 10^-3
• d = 1.306 +0.002/-0.004
• tE = 71.1 +2.3/-2.4 days
OGLE-2005-BLG-071: from double-lens to triple-lens (contours of parameters)
OGLE-2005-BLG-071: from double-lens to triple-lens (one example)
• q1 = 2.49 × 10^-3, d1 = 1.303• q2 = 4.99 × 10^-3, d2 = 1.304• φ = 3 degree (there is a range!)
Upgraded Microlensing Experiments
• OGLE IV is running in full power since 2011: 1.4 Deg2
camera
• MOA-II has been online:
1.8m telescope2.2 Deg2 camera
Detections
Earth mass
Mars mass
<Mercury mass
0.75 degree
77 arcsec
Penny et al. (2012)