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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2 March 20095
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 !
Stéphanie RenardTübingen Conference
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”