Roxanne LIGI
Doctorante sous la direction de Denis Mourard
Observatoire de la Côte d’Azur, Nice, France
Laboratoire Lagrange, UNS/CNRS/OCA
DÉTECTION D’EXOPLANÈTES EN
TRANSIT
ET
IMPACT DE L’ACTIVITÉ STELLAIRE
EN INTERÉROMÉTRIE OPTIQUE
Introduction
 Nowadays, more than 800 exoplanets have been detected
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Radial velocity (RV): most prolific method
Transit method (a few thousand Kepler candidates)
Astrometry
Microlensing…
 Difficulties to characterize them:
 RV  Mpl sin i / M*
 Transit method  Rpl / R*
 Better precision on the stars parameters  exoplanets parameters.
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1. INTERFEROMETRIC STUDY OF EXOPLANET HOST STARS
1.1 Choice of targets
 Now able to measure diameters with 2% accuracy, which allows having
sufficient informations on fundamental parameters (mass, radius,
temperature).
 Exoplanet host stars observable by VEGA/CHARA:
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F, G, K type stars
0.3 mas < θ* < 3 mas
Mag V < 6.5 and Mag K < 6.5
-30° < δ < +90°
Observations from April to December
 Host stars accessible with VEGA/CHARA:
42 stars.

35.7% V
 52.4% III
 11.9% IV
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Among them, only 1
transiting exoplanet, BUT 18
transiting exoplanets with
magV<10 that will be
observable with VEGAS,
VEGA second generation...
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1. INTERFEROMETRIC STUDY OF EXOPLANET HOST STARS
1.2 VEGA
 Six 1-m telescopes arranged in Yshape.
 Baselines between 34m and 331m.
 VEGA: Visible spEctoGrAph and
interferometer
– Up to 4T configuration, but mainly
3T
– V band
– Resolution: 6000/30000
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1. INTERFEROMETRIC STUDY OF EXOPLANET HOST STARS
1.2 Published Results (Ligi et al., 2012)
 14 And
 HD221345, HIP116076,
HR8930
 One exoplanet: 4.8 MJup
 K0III
 V mag = 5.22, K mag = 2.33
 (Sato et al., 2008)
 42 Dra
 HD170693, HIP513, H
 One exoplanet: 3.88±0.85 Mjup
 K1.5III
 (Döllinger et al., 2009)
 θ Cyg
HD185395
F4V
Kepler target
Quasi-periodical radial velocity of
~150 days unexplained (with
ELODIE and SOPHIE, OHP)
 (Desort et al., 2009).
 And
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HD9826, HIP7513, H
Hosts four exoplanets
F9V
(Furhmann et al., 1998))
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1. INTERFEROMETRIC STUDY OF EXOPLANET HOST STARS
1.2 Published Results (Ligi et al., 2012)
θLD = 1.18 ± 0.01 mas
χ2reduced = 6.9
θUD = 1.12 ± 0.01 mas
θLD = 2.12 ± 0.02 mas
χ2reduced = 0.199
θLD = 1.97 ± 0.02 mas
θLD = 0.76 ± 0.003 mas
χ2reduced = 8.5
θLD = 0.726 ± 0.032 mas
θLD = 1.51 ± 0.02 mas
χ2reduced = 2.769
θUD = 1.40 ± 0.02 mas
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1. INTERFEROMETRIC STUDY OF EXOPLANET HOST STARS
1.2 Published Results (Ligi et al., 2012)
 Radius:
 Mass:
 Effective temperature:
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Results in good agreements
with results found in the litterature!
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1. INTERFEROMETRIC STUDY OF EXOPLANET HOST STARS
1.2 On-going Results (Ligi et al., in prep.)
HD167042
HD 3651
 Host star, θUD expected ≈ 0.80 Host stars θUD expected ≈ 0.70
mas, magV = 5.97
mas, magV = 5.80
1 exoplanet
 1 exoplanet
2 observations, 720 nm
 2 obervations, 720 nm
θUD meas. ≈ 1.15±0.015 mas
 θUD meas. ≈ 1.00±0.014
χ2red = 0.50
mas
 04/06/13
χ2red = 0.58
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55 Cancri
Host star, θUD expected ≈ 0.70
mas, magV = 5.95
5 exoplanets,
(1 transiting).
3 observations, 720 nm
θUD meas. ≈ 0.63±0.011 mas
χ2red = 0.43
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2. MODELLING OF EXOPLANET HOST STARS AND SPOTS
2.1 COde for Modelling ExoplaneTs and Spots (COMETS)
 Evaluate the detectivity of exoplanets by interferometry in the visible
(taking into account periodical noises such as spots).
 Impact of stellar noises, like magnetic spots?


RV (Lagrange et al. 2010, Meunier et al. 2010).
IR interferometry (Matter et al., 2010).-> exoplanets
 COMETS (COde for Modeling ExoplaneTs and Spots): modelling of
visibilities and closure phases for exoplanets and spots, obtained with
VEGA/CHARA or a fictive (u,v) plan.


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Evaluation by analytical formula and numerical computation.
IDL code
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2. MODELLING OF EXOPLANET HOST STARS AND SPOTS
2.1 COde for Modelling ExoplaneTs and Spots (COMETS)
Example: 55 Cnc observed with VEGA/CHARA, oifits file made with ASPRO2.
θpl=0.015 mas.
 Visibilities: nothing is detected.
 Closure phase: the signal does not exceed 1°.
Visibility modulus
Closure phase (deg)
single star
star+ transiting exoplanet
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Spacial frequency (cyc/rad)
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Time
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2. MODELLING OF EXOPLANET HOST STARS AND SPOTS
2.1 COde for Modelling ExoplaneTs and Spots (COMETS)
Example: 55 Cnc observed with VEGA/CHARA, oifits file made with ASPRO2.
θpl=0.15 mas.
 Visibilities: reach 6% difference close to the zero of visibility.
 Closure phase: the signal reaches 120°.
Visibility modulus
Closure phase (deg)
single star
star+ transiting exoplanet
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Spacial frequency (cyc/rad)
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Time
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2. MODELLING OF EXOPLANET HOST STARS AND SPOTS
2.2 Method
We fix all parameters but one, and
make it vary.
 Fixed values: θ*=1 mas, Ipl=0,
x=0.2 mas, α=0.5.
 Variation:
 Of x: from 0 to 0.5 mas
 Of θpl: from 0.04 to 0.24
 Of α for studying the impact
of LD: from 0.44 to 0.74.
 α, x fixed, and variation of θpl/θ*
(steady ratio).
 α, x, θspot, θ* fixed, variation of
Ispot.
θpen, Ipen
θom,Iom
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2. MODELLING OF EXOPLANET HOST STARS AND SPOTS
2.3 Results
Variation of the Visibility:
No solution is found for θpl< 0.13 mas
for 2% difference. For θpl< 0.09 mas,
much larger baselines are needed.
Variation of the closure phase:
CHARA baselines exist.
+ 2% difference
* 1% difference
2° difference
20° difference
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2. MODELLING OF EXOPLANET HOST STARS AND SPOTS
2.3 Results
For exoplanets
In general, very small exoplanets (θpl< 0.10 mas) need MBL>200m to be detected
on the closure phase.
Having more than 2% difference on the visibilities is not possible.
 Need of the closure phases more than the visibility
For now, only big exoplanets (hot Jupiter, Neptune-like planets) have a chance to
be detected by interferometry.
For spots
Less contrast with spots than exoplanets  need bigger baselines
The intensity of the spot would allow to disentangle between spots and
exoplanets.
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2. MODELLING OF EXOPLANET HOST STARS AND SPOTS
2.4 Comparison between exoplanets and spots
Legend:
Single star
Star
+ transiting
exoplanet
Star + spot
Star + spot and
exoplanet
One direction, θpl = θom= 0.15
mas, , θp*= 1 mas.
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 Maximum difference
of 0.4% for
exoplanet+ spot
 Better seen in the 1st
and 2nd lobe of
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2. MODELLING OF EXOPLANET HOST STARS AND SPOTS
2.4 Comparison between exoplanets and spots
Legend:
Single star
Star
+ transiting
exoplanet
Star + spot
Star + spot and
exoplanet
One direction, θpl = θom= 0.15
mas, , θp*= 1 mas.
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 Maximum difference
of 150° for
exoplanet+ spot
 Better seen on the
transitions
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CONCLUSION
 Exoplanets and spots have a signature in optical interferometry.
 More significant signature for exoplanets than for spots for the same size,
because the contrast is higher.
 With VEGA/CHARA accuracy, we would distinguish spots and exoplanets
essentially with the measure of the closure phase, but signature on the
visibility for big enough planets and spots.
 The presence of spots hardly affects the visibilities, thus the diameters.
 Limitation: geometrical model, taking into account only one feature at the
time. We could model a full spotted stellar surface for more accuracy, and
even with granulation..
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MERCI
de votre attention