Discovery of a cool 5.5 Earth-mass planet through gravitational microlensing
description
Transcript of Discovery of a cool 5.5 Earth-mass planet through gravitational microlensing
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006
Discoveryof a
cool 5.5 Earth-mass planet through
gravitational microlensing
Arnaud CassanAstronomisches Rechen-Institut (ARI),Zentrum für Astronomie der Universität Heidelberg (ZAH)
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006
The microlensing effect
Observer
lens plane source plane
Source
< mas
Image
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006
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Magnification:
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Magnification curves
Einstein ring radius:
SL
LSE DD
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c
GM2
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(t-t0)/tE
The single lens case
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006
• Image separation :
• Einstein radius crossing time :
• Maximum amplification :
unresolved images !
Flux magnification monitoring
mas6.0
km/s200,kpc8,kpc6 :With
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solE
SLSL
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M
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maxmax uu
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Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006
Why a network of telescopes ?
• Ongoing microlensing events alerted by OGLE, MOA (EROS, MACHO)
Days
• Follow-up network : PLANET collaboration
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006
”Homebase” :- light curves modeling- observational strategy- public alerts- anomaly predictions
Observatories Raw data
( on-line reduction )
Data reduction pipeline
Observational strategy
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006
Beaulieu et al., 2006, Nature 439, 437
31.7.05
10.8.05
OGLE 2005-BLG-390Lb : a cool 5.5 Earth-mass planet
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006
OGLE-2005-BLG-390
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 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 ) 4th Planet Formation Workshop MPIA, 1st March 2006
The mass of OGLE 2005-BLG-390Lb
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 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 ) 4th Planet Formation Workshop MPIA, 1st March 2006
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006
Microlensing event OGLE 2005-BLG-390:
A cool and distant planet of 5.5 Earth masses• third planet discovered through microlensing
• lowest-mass extra-solar planet so far, with large separation
• support of core-accretion theory of planet formation :
– discovery despite low sensitivity such low mass extra-solar planets are most likely very common
• microlensing searches will be able to measure the frequency of extra-solar planets ultimately (especially around M-dwarfs)
Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1st March 2006