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

Stéphanie RenardTübingen Conference

2 March 20092

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

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Astrophysical context: physical conditions in the close environment of young stellar 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

Dust

Wind

Accretion disk

Magnetosphere

Gas

Planet

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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 φ because of the

atmospheric turbulence Closure phases (asymmetry of the object)

Analysis of the data: Model fitting Image reconstruction Model independent

VLTI, ESO Paranal, Chile

I

V

φ ddm

k

i jφij

φjkφki

CPijk = φij + φjk + φki

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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)

Likelihood term: compatibility of the solution with the data

Prior penalty: Additional constraints

Gaussian statistic: ²

Weight factor

Fourier transform

Positivity of the solution Normalization Smoothness regularization

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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

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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)

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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 !

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2 March 20099

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

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1st YSO: HD 45677 – 4. Conclusions Best model according to the image reconstruction:

Star + off-centered Gaussian ring Physical interpretation: flared disk Radius 9 ± 0.14 mas

Inclination 35 ± 2 °

Position angle 78 ± 3.5 °

Shift x 0.5 ± 0.2 mas

Shift y -2 ± 0.1 mas

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

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2 March 200911

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

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2nd YSO: MWC 275 – 2. MIRA results

Consistent with previous work and jet direction

K B

and

H B

and

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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 issues of 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

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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”