Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1 st March 2006 Discovery...

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)


The microlensing effect

Observer

lens plane source plane

Source

< mas

Image


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


• 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


Why 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


Beaulieu et al., 2006, Nature 439, 437

31.7.05

10.8.05

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


OGLE-2005-BLG-390


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


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, 1 st March 2006 Discovery...

Documents

Transcript of Arnaud Cassan ( ARI / ZAH Heidelberg ) 4th Planet Formation Workshop MPIA, 1 st March 2006 Discovery...