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  Radial velocity (RV): most prolific method  Transit method (a few thousand Kepler candidates)   Astrometry Microlensing…  Difficulties to characterize them:   RV  M pl sin i / M * Transit method  R pl / R *  Better precision on the stars parameters  exoplanets parameters.

04/06/13 R. LIGI - SF2A 2013 2

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:  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 Among them, only 1 transiting exoplanet, BUT 18 transiting exoplanets with magV<10 that will be Host stars accessible with VEGA/CHARA: 42 stars.

 35.7% V  52.4% III  11.9% IV observable with VEGAS, VEGA second generation...

04/06/13 R. LIGI - SF2A 2013 3

1.

INTERFEROMETRIC STUDY OF EXOPLANET HOST STARS 1.2 VEGA  Six 1-m telescopes arranged in Y shape.

 Baselines between 34m and 331m.

 VEGA: Visible spEctoGrAph and interferometer – Up to 4T configuration, but mainly 3T – – V band Resolution: 6000/30000 04/06/13 R. LIGI - SF2A 2013 4

1.

INTERFEROMETRIC STUDY OF EXOPLANET HOST STARS 1.2 Published Results (Ligi et al., 2012) 

14 And

 HD221345, HIP116076, HR8930     One exoplanet: 4.8 M Jup K0III V mag = 5.22, K mag = 2.33

(Sato et al., 2008)



42 Dra

    HD170693, HIP513 , H One exoplanet: 3.88

± 0.85 M jup K1.5III

(Döllinger et al., 2009)

  

And

    HD9826, HIP7513 , H Hosts four exoplanets F9V

(Furhmann et al., 1998) )

04/06/13 R. LIGI - SF2A 2013

θ Cyg

 HD185395  F4V  Kepler target  Quasi-periodical radial velocity of ~150 days unexplained (with ELODIE and SOPHIE, OHP) 

(Desort et al., 2009).

5

1.

INTERFEROMETRIC STUDY OF EXOPLANET HOST STARS 1.2 Published Results (Ligi et al., 2012) θ LD = 1.18 χ 2 reduced ± = 6.9

θ UD = 1.12 ± 0.01 mas 0.01 mas θ LD = 2.12 χ 2 reduced ± 0.02 mas = 0.199

θ LD = 1.97 ± 0.02 mas 04/06/13 θ LD = 1.51 χ 2 reduced ± 0.02 mas = 2.769

θ UD = 1.40 ± 0.02 mas R. LIGI - SF2A 2013 θ LD = 0.76 χ 2 reduced ± = 8.5

θ LD = 0.726 ± 0.003 mas 0.032 mas 6

1.

INTERFEROMETRIC STUDY OF EXOPLANET HOST STARS 1.2 Published Results (Ligi et al., 2012)  Radius:  Mass:  Effective temperature: 04/06/13 Results in good agreements with results found in the litterature!

R. LIGI - SF2A 2013 7

1.

INTERFEROMETRIC STUDY OF EXOPLANET HOST STARS 1.2 On-going Results (Ligi et al., in prep.)     

HD167042

Host star, θ UD expected mas, magV = 5.97

≈ 0.80 1 exoplanet 2 obervations, 720 nm θ UD meas.

mas ≈ 1.00

± 0.014 χ 2 red = 0.58

HD 3651

 Host stars θ UD expected mas, magV = 5.80

 1 exoplanet ≈ 0.70  2 observations, 720 nm  θ UD meas.

≈ 1.15

 χ 2 red = 0.50

± 0.015 mas R. LIGI - SF2A 2013

55 Cancri

 Host star, θ UD expected mas, magV = 5.95

 5 exoplanets, ≈ 0.70 (1 transiting).

 3 observations, 720 nm  θ UD meas.

≈ 0.63

 χ 2 red = 0.43

± 0.011 mas 8

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.

 Evaluation by analytical formula and numerical computation.

 IDL code 04/06/13 R. LIGI - SF2A 2013 9

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 . θ pl =0.015 mas.

  Visibilities: nothing is detected.

Closure phase: the signal does not exceed 1 ° .

single star star+ transiting exoplanet 04/06/13 Spacial frequency (cyc/rad) R. LIGI - SF2A 2013 Time Time 10

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 . θ pl =0.15 mas.

  Visibilities: reach 6% difference close to the zero of visibility.

Closure phase: the signal reaches 120 ° .

single star star+ transiting exoplanet 04/06/13 Spacial frequency (cyc/rad) R. LIGI - SF2A 2013 Time Time 11

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, I pl =0, x=0.2 mas, α=0.5.

 Variation:  Of x: from 0 to 0.5 mas   Of θ pl : 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 θ pl /θ * (steady ratio).

 α, x, θ spot , θ * I spot .

fixed, variation of 04/06/13 R. LIGI - SF2A 2013 θ pen , I pen θ om ,I om 12

2.

MODELLING OF EXOPLANET HOST STARS AND SPOTS 2.3 Results Variation of the Visibility: No solution is found for θ pl < 0.13 mas for 2% difference. For θ pl < 0.09 mas, much larger baselines are needed.

Variation of the closure phase: CHARA baselines exist.

+ 2% difference * 1% difference 2 ° difference 20 ° difference 04/06/13 R. LIGI - SF2A 2013 13

2.

MODELLING OF EXOPLANET HOST STARS AND SPOTS 2.3 Results

For exoplanets

 In general, very small exoplanets (θ pl < 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.

04/06/13 R. LIGI - SF2A 2013 14

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

04/06/13 R. LIGI - SF2A 2013 One direction, θ pl = θ om = 0.15 mas, , θ p* = 1 mas.

  Maximum difference of 0.4% for exoplanet+ spot Better seen in the 1 st and 2 nd lobe of visibility 15

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

04/06/13 R. LIGI - SF2A 2013 One direction, θ pl = θ om = 0.15 mas, , θ p* = 1 mas.

  Maximum difference of 150 ° for exoplanet+ spot Better seen on the transitions 16

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..

04/06/13 R. LIGI - SF2A 2013 17

04/06/13

MERCI de votre attention

18