the circumstellar environment of evolved stars as seen by vlti / midi

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The circumstellar environment of evolved stars as seen by VLTI / MIDI Keiichi Ohnaka Max-Planck-Institut für Radioastronomie, Infrared Interferometry Group [email protected]

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The circumstellar environment of evolved stars as seen by VLTI / MIDI. Keiichi Ohnaka Max-Planck-Institut für Radioastronomie, Infrared Interferometry Group [email protected]. Carbon star, IRC+10216. AGB, AFGL2290. Asymptotic Giant Branch (AGB). Post-AGB Red Rectangle. - PowerPoint PPT Presentation

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Page 1: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

The circumstellar environment of evolved stars as seen by VLTI / MIDI

Keiichi OhnakaMax-Planck-Institut für Radioastronomie,Infrared Interferometry [email protected]

Page 2: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

Asymptotic Giant Branch (AGB) Post-AGB Red Rectangle Teff ~ 3000K

L ~ 104 L

Mass loss ~10-8—10-5 M/yr

Mass loss mechanism

The structure of the outer atmosphere:

Molecule & dust formation

Morphology from AGB to Planetary Nebulae

Carbon star, IRC+10216

AGB, AFGL2290

PN, Cat’s Eye Nebula

Page 3: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

Outer atmosphereMolecular layers

Near-infrared

Expanding dust shell

What can interferometry do to study AGB stars?

Mid-infrared

Dust formation

Mira variables: Large variability amplitude

~ 9 mag (in V)

MIDI AMBER

Page 4: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

Infrared long-baseline interferometry

Spatial resolution = /Bp

N bandBp = 200m 10mas

What’s observed: Visibility, not an image!

MIDI AMBER

Visibility = Amplitude of the (complex) Fourier transform

of the object’s intensity= Fringe contrast

Is it useful?Yes, especially with spectral resolution!

It “contains” information onthe angular size and shape

Point source V = 1 Extended source V < 1Larger size lower V

B p

Page 5: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

MIDI: first fringe in December 2002 Open to the community since April 2004

VLTI Interferometric

Laboratory

N band: 8 – 13 m (dust features, molecular bands) Spectral resolution: 30 / 230 Sensitivity @ m: 1 Jy / 10 Jy

Page 6: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

UT1 UT3

102m

MIDI observation of the Mira variable RR Sco2003 June, Science Demonstration Time

Unit Telescopes 1 & 3 (8m) Projected baseline = 74—100m Angular resolution @ 10m = ~20mas

RR Sco (Phase = 0.6 in 2003 June) P = 284 days, d = 320 pc (Hipparcos) Dust emission not strong Good for studying the molecular layers

Page 7: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

7.5m 13.3m

MIDI observation of RR Sco: spectrally dispersed fringes

Page 8: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

Observed N-band visibility of RR Sco

Visibility increases from 8 to 10 m, constant > 10 m UD diameter constant between 8 and 10 m (~18 mas), UD diameter increases > 10 m (~25 mas @ 13 m)

N-band UD diameter (MIDI) twice as large as that in the K band

(VINCI, 3 weeks later) Why?

Page 9: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

Observed N-band visibility of RR Sco

Page 10: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

Expanding dust shell

Optically thick emission from H2O (pure rotation) + SiO (fundamental) gas

+Dust emission

N band (8—13m)

H2O + SiO gas

K band (2—2.4m)No dust emission

H2O + CO bands Not optically thick Angular size smaller

Modeling H2O + SiO layer

(constant temperature, column densities, radius)

Optically thin dust shell (silicate+corundum) (Inner radius, optical depth)

Basic idea

Ohnaka et al. 2005, A&A, 429, 1067

Angular size larger

Page 11: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

H2O+SiO emission

Dust emission (silicate 20% + corundum 80%)

T = 1400 KN(H2O) = 3 x 1021cm-2

N(SiO) = 1 x 1020cm-2

R = 2.3 Rstar

Tin ~ 700 K, Rin = 7--8 Rstar = 0.2 – 0.3 (V band), 0.025 (10m) Comparison with pulsation models

is ongoing

Page 12: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

MIDI observation of the silicate carbon star Hen 38

Silicate carbon star : carbon-rich photosphere, oxygen-rich circumstellar dust

Usually… carbon star, carbon-rich circumstellar dust

(amorphous carbon, SiC) M giants (O-rich), oxygen-rich circumstellar dust

(silicate, Al2O3: corundum)

How can silicate (O-bearing dust) exist around a carbon star?

Page 13: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

Oxygen-rich dust(silicate) reservoir

Mass loss

AGB, primary star: oxygen-rich, mass loss Circumbinary disk is formed

Primary star becomes a carbon star.Oxygen-rich dust is stored in the disk Silicate carbon star

High-resolution observation in the silicate emission feature is the most direct approach VLTI/MIDI

AGB star + main sequence star

Page 14: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

Compact silicate disk + extended corundum disk

Silicate

Corundum (Al2O3)

Compact disk

Only present in the outer regionIncrease of the angular size m

Page 15: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

Silicate torus (ring) dominantCorundumdominant

Silicate + corundum disk model

15 – 35 Rstar, m) = 1.5 > 35 Rstar,

m) = 0.4

Page 16: The circumstellar environment of  evolved stars as seen by VLTI / MIDI

Concluding remarks

First “spectro-interferometric” observation of RR Sco Wavelength dependence of the angular size

Angular size constant between 8 and 10 m, increases longward of 10 m, More than twice as large as in the K-band

Observed N-band visibilities and spectra can be explained by optically thick emission from H2O + SiO gas & dust emission Consistent with ISO and previous results

Potential to probe the circumstellar environment (molecule and dust) with spatial and spectral information disentangled Totally new picture of the circumstellar environment

Upcoming: more Miras (oxygen-rich, carbon-rich, S-type), Circumstellar dust disks around (post-)AGB stars,

Symbiotic stars (Mira + hot companion), etc…