High Resolution Imaging of dust disks structures around Herbig

Ae stars with VISIR

• C.Doucet, P-O Lagage, E. Pantin (CEA Saclay SAp)• E. Habart (IAS, Orsay)• C. Pinte, G. Duchêne, F. Ménard (LAOG, Grenoble)

20-23 March 2006 - VIRA - Paris

VISIRVLT Imager and Spectrometer

for the InfraRed

• Located at the Cassegrain focus of UT3 of the VLT.

• 2 bands IR of obervations:– N Band : 8 - 13 μm – Q Band : 17 - 24 μm

• Spatial resolution: 15 times the ones of ISOCAM or Spitzer (0.075 ’’/pixel)

• Spectral resolution:– 350 - 25000 at 10 μm – 1200 - 12500 at 20 μm.

0.8’’ seeing

New imaging mode: BURST mode

• Seeing not as good as expected → lost spatial resolution

51

seeing

Seeing of 0.8’’ in the visible →Seeing of 0.4’’ in mid-IR→movement of 5 pixels.

→ Limit the effect of TURBULENCE by freezing the atmosphere with very

short exposure time :BURST MODE

Speckle in mid-IR0r

D

wavelength SEEING 0.5’’ SEEING 1’’

(µm) R0 (m) T0(ms) R0 (m) T0(ms)

2 1.05 52-210 0.52 28-100

10 7.28 360-1450 3.64 200-700

20 16.7 835-3340 8.36 400-1600

Wind speed between 5 and 20 m/s

250702

0

speckleNRD In Near-IR

42

0

speckleNRD In Mid-IR

→ Stable atmosphere

→ One principal speckle

Texposition ~ 16-50 (ms) ≤ T0(mid-IR)

D~R0

BURST: turbulence effect

Sensibility ↔ 7 mJy/10σ/1hSensibility ↔ 14 mJy/10σ/1h

Reference star HD85503 at 11.3 µm (January 2005)

Shift and add by centroid

Shift and add by autocorrelation

Shift and add by maximum

FWHMx (mas) 424 302 386

FWHMy (mas) 547 288 523

ellipticity 1.29 0.95 1.36

Strehl ratio 0.328 0.760 0.368

Image quality/shift and add in mid-IR

HD85503 at 11.3 µm (January 2005, seeing of 0.75’’ in the visible)HD62902 at 11.3 µm, Seeing of 1.2’’ in the visible Shift and add by centroid

Shift and add by autocorrelation

Shift and add by maximum

FWHMx (mas) 358 300 437

FWHMy (mas) 552 300 542

ellipticity 1.54 1. 1.24

Strehl ratio 0.27 0.80 0.67

Limit of the method

• For bright sources (5 Jy in N band)

• Method shift and add valid for a seeing ≤ 1.3’’ in the visible

Otherwise

→ speckle interferometry

Effect of a bad seeing (1.5 ’’) on the source

A star noticeable: HD97048a Herbig A star at 180 pc in the Chameleon cloud

Doucet et al. 2006,submitted A&A

PAH stochastically heated by UV radiation from the star Could allow to see the disk much further from the star: new TRACERS of the disk geometry

What could we learn from PAH emission?

First measure of the height versus the radius

H ∞ R1.5

Conclusions/Perspectives

HD169142 in mode normal (PAH1, 8.6 µm)0.65 ’’ seeing, exposure time: 316 sHD169142 in BURST mode (PAH1, 8.6 µm)0.55’’ seeing, exposure time: 118 s

• TRUST in BURST mode

• planned to be a technical mode

• Work with ESO to open thismode to community

PSF substracted

Sometimes, elongated source

Modelisation of a flared disk

Model of disk heated by irradiation from the central star, in hydrostatic equilibrium in the vertical direction, with dust and gaz well mixed, with transiently heated small grains and PAHs addition to large grains in thermal equilibrium (1-D radiation transfert code, Habart et al. 2004).