microlensing search for extra-solar planets from dome c

Arnaud Cassan Optical and Infrared Wide-Field Astronomy in AntarcticaARI / ZAH Heidelberg IAP, 14 – 16 June 2006

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


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


The Gravitational microlensing effect

► Magnification of the source star flux

• Probing the Galactic Halo (MACHO, EROS)

• Galactic structure (OGLE, MACHO, EROS)

• Search for extra-solar planets (PLANET, MOA, MicroFun)


Observations toward the Bulge

Probability of a microlensing event : 10-6

observations toward the BulgeOGLE fields

Dome C is definitely the best site to observe the Bulge from Earth


• Image separation :

• Einstein radius crossing time :

• Maximum amplification :

unresolved images !

Flux magnification monitoring

mas6.0

km/s200,kpc8,kpc6 :With

*

/

solE

SLSL

M

M

vDD

daysM0.2

M 30

sol

L

/

SL

LEE v

Dt

0when 1

1002 minmin

maxmax uu

AA

3 - 4 weeks continuous observations from Dome C


The « standard » multi-site setup: a network of telescopes

• Ongoing microlensing events alerted by OGLE, MOA (EROS, MACHO)

Days

• Follow-up network : PLANET collaboration


”Homebase” :- light curves modeling- observational strategy- public alerts- anomaly predictions

Observatories Raw data

( on-line reduction )

Data reduction pipeline

Observational strategy

BUT requires many “manual” operations…

One site allow much more automated

procedures, from data reduction to data

analysis and modeling


MOA 2003-BLG-53Lb : a Jupiter-like planet


OGLE-2005-BLG-071Lb : another Jupiter-like planet


OGLE-2005-BLG-390Lb a 5.5 Earth-mass planet


OGLE-2005-BLG-169Lb : a weak Neptune plant signal

Gaps in the coverage difficulties in modeling and finding a unique model


Detection efficiencies

Cassan et al., 2006, en préparation

[1] Modeling of individual events, e.g. :

[2] Statistical combination of the individual efficiencies


Microlensing detection efficiencies 1995 - 2006

Cassan et al., 2006, en préparation

These planets of few Earth masses and few AU orbits may be very common

A continuous monitoring from Dome C would push the detection efficiency limits toward low-mass stars


Limits on abundance of exoplanets

• No strong selection with star brightness (only the lens mass is involved)

• The « whole » range of star mass is probed (prop. to their abundance)

Gaudi et al. 2000

Ultimately, microlensing can provide a good estimation

of Galactic planet abundance


Multiple planetary systems

Kubas, Cassan et al. (in preparation)

Ex. Constraints on additional Jupiter-like planets on OGLE-2005-BLG-390


Complementary to other methods


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


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


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


A possible setup

• A 2m-class telescope• 28k x 28k camera

0.09”/pixel -> 0.5deg2 FOVFWHM 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


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


4

2)(

2

2

uu

uuA

Magnification:

u

Magnification curves

Einstein ring radius:

SL

LSE DD

D

c

GM2

*4

(t-t0)/tE

The single lens case


Model predictions vs. microlensing observation

OGLE 2005-BLG-390Lb

Ida & Lin, 2005, ApJ 246, 1045

Cassan & kubas (in preparation)


Crowded fields


Galactic microlensing


Beaulieu et al., 2006, Nature 439, 437

31.7.05

10.8.05

OGLE 2005-BLG-390Lb : a cool 5.5 Earth-mass planet


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


The mass of OGLE 2005-BLG-390Lb


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


Détection des exoplanètes

Juillet 2003

(Planète jovienne)

Mai 2005

(Planète jovienne)

Bond et al., 2004, ApJ 606 Udalski et al., 2005, ApJ 628


Microlentilles doubles : caustiques et courbes critiques

Caustiques (plan-source)Courbes critiques (plan-lentille)

intermédiaireSéparation : grande

faible


The microlensing effect

Observer

lens plane source plane

Source

< mas

Image


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)

microlensing search for extra-solar planets from dome c

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