Microlensing search
for extra-solar planets
from Dome C
Arnaud Cassan
Astronomisches Rechen-Institut (ARI),
Zentrum für Astronomie der Universität Heidelberg (ZAH)
J.-P. Beaulieu, P. Fouqué, J.-B. Marquette, C. Coutures
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Outline
1/ The microlensing method
2/ The current observing setup
3/ Results and capabilities of the method
4/ Why observing from Dome C ?
5/ Summary & conclusion
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
The Gravitational microlensing effect
• Probing the Galactic Halo (MACHO,
EROS)
• Galactic structure (OGLE, MACHO,
EROS)
• Search for extra-solar planets
(PLANET, MOA, MicroFun)
► Magnification of the source star flux
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Observations toward the Bulge
Probability of a microlensing event : 10-6
 observations toward the Bulge
OGLE fields
Dome C is definitely the best site to observe the Bulge from Earth
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
• Image separation :
With : DL  6 kpc,
 E  0.6
DS  8 kpc, vL / S  200 km/s
M*
mas
M sol
 unresolved images !
 Flux magnification monitoring
• Einstein radius crossing time :
tE 
 E DL
vL / S
ML
 30
days
0.2 Msol
3 - 4 weeks continuous
observations from Dome C
• Maximum amplification :
Amax  2  100
Arnaud Cassan
ARI / ZAH Heidelberg
Amax 
1
umin
when umin  0
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
The « standard » multi-site setup: a network of telescopes
• Ongoing microlensing
events alerted by
OGLE, MOA
(EROS, MACHO)
• Follow-up network :
PLANET collaboration
Days
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Observational strategy
Observatories
Raw data
Data reduction pipeline
BUT requires many
( on-line reduction )
“manual” operations…
 One site allow much more
automated procedures,
from data reduction to data
analysis and modeling
-
Arnaud Cassan
ARI / ZAH Heidelberg
”Homebase” :
light curves modeling
observational strategy
public alerts
anomaly predictions
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
MOA 2003-BLG-53Lb : a Jupiter-like planet
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
OGLE-2005-BLG-071Lb : another Jupiter-like planet
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
OGLE-2005-BLG-390Lb a 5.5 Earth-mass planet
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
OGLE-2005-BLG-169Lb : a weak Neptune plant signal
Gaps in the coverage
 difficulties in modeling
and finding a unique model
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Detection efficiencies
 [1] Modeling of individual events, e.g. :
Cassan et al., 2006, en préparation
 [2] Statistical combination of the individual efficiencies
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Microlensing detection efficiencies 1995 - 2006
These planets of few Earth
masses and few AU orbits may
be very common
A continuous monitoring from Dome C
Cassan
et al., 2006,
en préparation
would push the
detection
efficiency
limits toward low-mass stars
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Limits on abundance of exoplanets
Ultimately, microlensing can provide a good estimation
of Galactic planet abundance
Gaudi et al. 2000
• No strong selection with star brightness (only the lens mass is involved)
• The « whole » range of star mass is probed (prop. to their abundance)
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Multiple planetary systems
Ex. Constraints on additional Jupiter-like planets on OGLE-2005-BLG-390
Kubas, Cassan et al. (in preparation)
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Complementary to other methods
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Main goals of microlensing
• Detection of Neptune to Earth-mass planets
• Abundance of extra-solar planets in the Galaxy
From space simulations (MPF satellite, Bennett et al. 2005) :
– 66 terrestrial planets
– 100 icy giants
– 3300 gas giants
 Order of magnitude of what may be expected from Dome C
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Why Dome C ?
With he current setup :
– Gaps in the light curve
– Multi-site photometry = difficulties with combining data sets from
different telescopes (mean seeing/air mass, weather conditions, CCDs…)
– Australia do not provide stable weather conditions to operate a deep
round-the-clock monitoring
 Only 1 terrestrial planet so far
Given that :
- the theoretical efficiency is higher than is achievable now
- the main difficulties come from
- the non-continuous monitorin
- The weather conditions
- the statistical point of view is the most relevant for microlensing search for
exoplanets
► The ground base detection capabilities have been reached
► Dome C is the most relevant site to achieve the ultimate goal of
microlensing searches for exoplanets = statistical aspect
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
What would Dome C provide for microlensing
towards the Bulge ?
• Continuous monitoring of the Bulge
• Stable weather condition  eliminate false alerts
• Stable and good seeing, low background
• One telescope with one instrument  high
improvement of photometry precision + known
systematic errors
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
A possible setup
• A 2m-class telescope
• 28k x 28k camera
0.09”/pixel -> 0.5deg2 FOV
FWHM 0.25’’
• 2 deg2 monitored in the Bulge
• Time Sampling : every 20 min
• During Antarctica winter season: in 2005 (sun < -18 deg) -> 81 days
• 3 – 4 weeks continuous observations (time scale < 30 d)
• A OGLE-like alert + following setup
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Summary & Conclusion
• 4 extra-solar planets discovered :
– 2 Jupiter-like + 1 Neptune planets (2003-2006)
– A 5.5 Earth-mass planet (2006)
• Abundance of exoplanets around M-dwarfs
– will ultimately extend to “all” stars
• Sensitivity/limits on multi-planetary systems
• Complementary to other techniques (ex. RV)
• Dome C is the only site on Earth that allows a continuous monitoring
of the Galactic Bulge
• A realistic project :
– Experience from an ongoing project (10 years with PLANET)
– Expertise of data reduction/image subtraction technique
– Expertise in modeling, statistical analysis
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
The single lens case
Magnification curves
u
Einstein ring radius:
4GM* DLS
E 
c 2 DL DS
Magnification:
A(u ) 
u2  2
u u2  4
(t-t0)/tE
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Model predictions vs. microlensing observation
Cassan & kubas (in preparation)
OGLE 2005-BLG-390Lb
Ida & Lin, 2005, ApJ 246, 1045
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Crowded fields
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Galactic microlensing
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
OGLE 2005-BLG-390Lb : a cool 5.5 Earth-mass planet
10.8.05
31.7.05
Beaulieu et al., 2006, Nature 439, 437
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
What we know from the unique modeling
• Planet/star mass ratio :
q = mp / M* = (7.6 ± 0.7) x 10-5
• Instantaneous separation/Re :
d = rphys / RE = 1.61 ± 0.01
• Source star distance :
DS = 8.5 kpc
• Einstein ring crossing time :
tE = 11.0 ± 0.1 days
RE = vt tE = 1/c [ 4GM*DL(1-DL/DS) ]1/2
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
The mass of OGLE 2005-BLG-390Lb
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Deriving physical parameters
• Planet mass & orbit :
mp = 5.5 +5.5-2.7 Earth-mass
ap = 2.6 +1.5-0.6 AU
• Host star :
M* = 0.2 +0.2-0.1 Msol
• Lens distance :
DL = 6.6 ± 1 kpc
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Détection des exoplanètes
Juillet 2003
Mai 2005
(Planète jovienne)
(Planète jovienne)
Bond et al., 2004, ApJ 606
Arnaud Cassan
ARI / ZAH Heidelberg
Udalski et al., 2005, ApJ 628
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
Microlentilles doubles : caustiques et courbes critiques
Courbes critiques (plan-lentille)
Séparation :
Arnaud Cassan
ARI / ZAH Heidelberg
Caustiques (plan-source)
intermédiaire
grande
faible
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
The microlensing effect
lens plane
source plane
Image
< mas
Source
Observer
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006
The PLANET collaboration
(Probing Lensing Anomalies NETwork)
M. D. Albrow, J.P. Beaulieu, D. Bennett, S. Brillant, J. A. R. Caldwell, H.
Calitz, A. Cassan, K. Cook, C. Coutures, M. Dominik, J. Donatowicz, D.
Dominis, P. Fouqué, J. Greenhill, K. Hill, M. Hoffman, K. Horne, U.
Jorgensen, S. Kane, D. Kubas, R. Martin, J. Menzies, P. Meintjes, K. R.
Pollard, K. C. Sahu, J. Wambsganss, A. Williams
ARI Heidelberg (Germany), IAP Paris (France), Univ. of Notre Dame (USA), Univ. of
Canterbury (New Zealand), SAAO (South Africa), Boyden Observatory (South Africa),
Canopus Observatory (Tasmania), Niels Bohr Institute (Denmark), Univ. of Potsdam
(Germany), STSI (USA), Perth Observatory (Australia), ESO (Chile), OMP (France)
Arnaud Cassan
ARI / ZAH Heidelberg
Optical and Infrared Wide-Field Astronomy in Antarctica
IAP, 14 – 16 June 2006