Milli-arcsecond Imaging of the Inner Regions of Protoplanetary Disks

1. Milli-arcsecond Imaging of the Inner Regions of Protoplanetary Disks Stéphanie Renard In collaboration with F. Malbet, E. Thiébaut, J.-P. Berger & M. Benisty « Planet Formation and Evolution: The Solar System and Extrasolar Planets » Tübingen, 2 March 2009

2. Outline • Astrophysical context: • Protoplanetary disks around young stellar objects (YSOs) • Optical/IR interferometry: • Technique & Observables • Image reconstruction • Application on real data of YSOs: • HD 45677 • MWC 275 • Conclusions & Perspectives Tübingen Conference 2 March 2009

3. Dust Magnetosphere Planet Accretion disk Gas Wind Astrophysical context: physical conditions in the close environment of youngstellar objects • Characteristics & Phenomena • Stars from 4000 to 10000K • Accretion disk (Keplerian or not): gas + dust • Strong outflowing winds • Companions • Magnetospheric accretion • Protoplanets • Physical conditions of the dust inner disk: • Radius from 0.1 to 10 AU • Temperature from 150 to 4000K • Velocity from 10 to a few 100 km/s  Instrument requirements: • 1 µm ≤  ≤ 10 µm • Spatial resolution from 0.5 to 70 mas (at 150 pc ; Taurus system)  Optical/IR Interferometry Tübingen Conference 2 March 2009

4. VLTI, ESO Paranal, Chile I V ddm φ φij j i φjk k φki Optical/IR interferometry: observables • Concept: • Coherent recombination of the beams from several telescopes  High angular resolution • Observables: fringe pattern • Squared visibilities V (size of the object) • Loss of phase φbecause of the atmospheric turbulence  Closure phases (asymmetry of the object) • Analysis of the data: • Model fitting • Image reconstruction  Model independent CPijk = φij + φjk + φki Tübingen Conference 2 March 2009

5. Optical/IR interferometry: image reconstruction • Image formation • Goal of image reconstruction: retrieve I true • Ill-conditioned problem (infinity of solutions which fit the data in the error bars)  additional constraints • Method: Maximum a posteriori • Use of MIRA algorithm of Eric Thiébaut (Thiébaut et al. 2008, Proc. SPIE 7013, 70131I)  Fourier transform Prior penalty: Additional constraints Likelihood term: compatibility of the solution with the data • Positivity of the solution • Normalization • Smoothness regularization Gaussian statistic: ² Weight factor Tübingen Conference 2 March 2009

6. 1st YSO: HD 45677 – 1. Description • Herbig Be type (?) • Monnier et al. 2006 “First closure phase survey of Herbig Ae/Be stars”  parametric imaging  highly skewed dust ring (i.e. the brightest part of a disk in the NIR infrared) • Data used for the image reconstruction: • Monnier et al. 2006 • IOTA interferometer • H Band Monnier et al. 2006 Tübingen Conference 2 March 2009

7. 1st YSO: HD 45677 – 2. MIRA results • Reconstructed image (reduced ²~2): central star + clumpy features on an ellipse (?!) • Prior: smoothness (independent of the chosen prior) Tübingen Conference 2 March 2009

8. 1st YSO: HD 45677 – 3. Analysis • Method: • Choose a model (e.g. star + Gaussian ring) • Compute the Fourier Transform of the model and determine the squared visibilities & closure phases • Take the observables exactly at the same u,v points than the real data • Keep the same error bars than the real data • Reconstruct a new image  Try to find a model which gives a reconstructed image as close as possible to the one from the real data • 1st model: star + Gaussian ring • Problem: symmetric model  closure phases = 0 ! Tübingen Conference 2 March 2009

9. 1st YSO: HD 45677 – 3. Analysis • 2nd model: star + skewed Gaussian ring • Problem: features only on a side of the star • 3rd model: star + off-centered Gaussian ring Tübingen Conference 2 March 2009

10. 1st YSO: HD 45677 – 4. Conclusions • Best model according to the image reconstruction: • Star + off-centered Gaussian ring • Physical interpretation: flared disk • Need data at longer baselines in order to distinguish between different models • Image reconstruction: • The features seem to be an intern problem: why and how avoid them ? (work in progress) • New approach: determination of new models by the image reconstruction results Monnier et al. 2006 Tübingen Conference 2 March 2009

11. 2nd YSO: MWC 275 – 1. Description • Herbig Ae star • Data used for the image reconstruction: • Benisty et al., in prep • VLTI/AMBER interferometer • spectral dispersion over H and K band • Devine and Grady et al. 2000 “A Ly bright jet from a Herbig Ae Star”:  Collimated bipolar outflow (HH409) perpendicular to the disk Tübingen Conference 2 March 2009

12. 2nd YSO: MWC 275 – 2. MIRA results K Band Consistent with previous work and jet direction H Band Tübingen Conference 2 March 2009

13. Conclusions & Perspectives • First images on real interferometric data of complex YSOs • New approach: determination of new models by the image reconstruction results • Work on one of the issuesof YSOs: the disk shape • Image reconstruction in optical interferometry: a new technique in progress • Difficulties (in contrast to image reconstruction in radio): • Sparse (u,v) coverage • Lack of phase information  systematic tests on the MIRA algorithm • Reconstructed images independent of the added constraints  robust results  First steps towards the 1mas-imaging with the new imager instruments at VLTI Tübingen Conference 2 March 2009

14. Thank you for your attention • Another astrophysical object: The Mira Star T Lep Le Bouquin et al. 2009, A&A Letter “Pre-maximum spectro-imaging of the Mira star T Lep with AMBER/VLTI” Tübingen Conference 2 March 2009