Transcript Microlensing WG review - Pathways Towards Habitable Planets

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
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.
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 10-6
– Planetary lensing probability
~0.001-1 depending on
event details
• Peak sensitivity is at 2-3 AU:
the Einstein ring radius, RE
Einstein’s
telescope
Microlensing Target Fields are in the
Galactic Bulge
Galactic center
8 kpc
Sun
1-7 kpc from Sun
Light curve
Source star
and images
Lens star
and planet
Telescope
10s of millions of stars in the Galactic bulge in order to detect planetary
companions to stars in the Galactic disk and bulge.
How Low Can We Go?
Limited by Source Size
angular Einstein radius
Mp 
 E   as 

 M °Ú 
1/2
R 
*  as  * 
 R°—
angular source star radius
(Bennett & Rhie 1996)
For E  * :
Mars-mass planets detectable
low-mass planet signals are rare and
if solar-type sources can be
brief, but not weak
monitored!
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
Survey
Telescopes
PLANET
Network
KMTNet
KMTNet
MOA
High
Magnification
Alert!!
OGLE
FUN
Network
KMTNet
CTIO
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= *tE/t* and projected Einstein radius, r%
E
– * = the angular radius of the star
– r%
E from the microlensing parallax effect (due to Earth’s orbital motion).
2
r%
4GM
c
RE   E DL , so   E  2
. Hence M 
 E r%
E
DL c  E DL
4G
Finite Source Effects & Microlensing
Parallax Yield Lens System Mass
• If only E or rE 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, rE , and lens star
brightness, we have more
constraints than parameters
mass-distance relations:
c 2 2 DS DL
ML 
E
4G DS  DL
c 2 DS  DL
ML 
r%
E
4G
DS DL
2
c2
ML 
r%
E E
4G
Space-based parallaxes using Solar System Science Spacecraft?
Double-Planet Event: OGLE-2006-BLG-109
• 5 distinct planetary
light curve features
• OGLE alerted 1st
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 Saturnmass 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
Planetary orbit changes the caustic curve
- plotted at 3-day intervals
Feature
due to
Jupiter
OGLE-2006-BLG-109 Source Star
Apparent source
In image
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
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  17.17
– JHK observations will help to constrain the extinction toward the lens star
Implications of Light Curve Model
Host star mass: M L  0.52 0.18
0.07 M e from light curve model.
• Apply lens brightness constraint: HL 17.17.
• Correcting for extinction: HL0= 16.93  0.25
– Extinction correction is based on HL-KL color
– Error bar includes both extinction and photometric uncertainties
• Lens system distance: DL= 1.54  0.13 kpc
Host star mass: M L  0.51  0.05M e from light curve and
lens H-magnitude.
Other parameter values:
• “Jupiter” mass:
semi-major axis:
• “Saturn” mass:
semi-major axis:
• “Saturn” orbital velocity
eccentricity
inclination
mb= 0.73  0.06 MJup
ab  2.3  0.5AU
mc= 0.27  0.03 MJup= 0.90 MSat
ac  4.5 2.2
1.0 AU
vt = 9.5  0.5 km/sec
  0.15 0.17
0.10
i = 63  6
Current Event: MOA-2009-BLG-266
• Planet discovered by
MOA on Sept. 11, 2009
• Low-mass planet
– Probably
 10M 
• 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
Ground-based confusion, space-based resolution
CTIO
HST
MPF
• 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
Lens Star Identification from Space
• Lens-source proper motion
gives E = reltE
• 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
Simulated HST images:
ML= 0.08 M
ML= 0.35 M
– 2 native resolution
– also detectable with HST
WFPC2/PC & NICMOS/NIC1
ML= 0.63 M
• Stable HST PSF allows clear
detection of PSF elongation
signal
• A main sequence lens of any
mass is easily detected (for
this event)
raw image
PSF subtracted
binned
The Microlensing Planet Finder
(MPF)
David Bennett, PI
Ed Cheng, Deputy PI
NASA/GSFC Management
Lockheed Martin, prime contractor
MPF Complements Kepler
Figures from B.
MacIntosh of the
ExoPlanet Task Force
MPF’s Predicted Discoveries
Planet Type
q
Earth/Venus/Mars 0.3-310-6
The number of expected MPF planet
discoveries as a function of planet
mass.
Discoveries
150
Jupiter
10-3
5000
Saturn
310-4
1000
Uranus/Neptune
510-5
130
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.
From the ExoPlanet Task Force:
• “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.
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