Armando DOMICIANO de SOUZA

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Armando DOMICIANO de SOUZA
The vicinity of galactic supergiant Be stars
from IR long baseline interferometry with the
VLTI
Main collaborators O. Chesneau (OCA, F), T.
Driebe (MPIfR, D), K-.H. Hofmann (MPIfR, D), S.
Kraus (MPIfR, D), A. Miroshnichenko (UT, US), K.
Ohnaka (MPIfR, D), P. Stee (OCA, F), G. Weigelt
(MPIfR, D)
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Plan

• Introduction
• The Be phenomenon
• Principles of optical/IR long baseline
  interferometry
• VLTI (MIDI and AMBER) observations of CPD-57 2874
• VLTI-MIDI (visibilities, spectrum, modelling,
  comparison to other data)
• VLTI-AMBER (visibilities, modelling, phases)
• Comparison of VLTI-MIDI and VLTI-AMBER results

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The Be phenomenon(Lamers et al. 1998)
1. Strong Balmer emission lines. 2. Low
excitation permitted emission lines of
predominantly low ionization metals in the
optical spectrum, e.g. Fe II. 3. Forbidden
emission lines of Fe II and O I in the
optical spectrum. 4. A strong near or
mid-infrared excess due to hot circumstellar dust.
Meilland
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The Be phenomenon(Lamers et al. 1998)
Supergiants Be ? L/Lsun gt 104
Observations point towards asymmetrical stellar
environments
Zickgraf et al. (1985)
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Principles of optical/IR long baseline
interferometry
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Principles of optical/IR long baseline
interferometry
Interference fringes
?
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Interferometry the uv or Fourier plane
u and v ? spatial frequency Bproj / l
Partial uv coverage ? Models are needed to
interpret the current interferometric observations
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Observations of Be stars with VLTI-MIDI and
VLTI-AMBER
Observational set-up MIDI N band with R30
(8-13 ?m) Unit Telescopes (UTs) 2
baselines AMBER K band with R1200 (2.1-2.2
?m) Unit Telescopes (UTs) 3 baselines (closure
phase)
Targets GG Car MIDI Not well resolved (size lt
10 mas) CPD-57 2874 MIDI and AMBER
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VLTI-MIDI observations
Equivalent uniform disc model V(l) 2J1(z) /
z , where z p qUD(l) Bproj / l
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VLTI-MIDI observations
UD diameter versus Position Angle
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VLTI-MIDI fit of V with gaussian-modelsChromati
c variation of the major axis FWHM ? 2a 2a0 K
(?-?0)
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VLTI-MIDI spectrum
Possible origin of this featureless spectrum
around 10 ?m Large grains ? Carbonaceous dust
? Free-free emission ? Additional opacity sources
?
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Modelling VLTI-MIDI observations
Envelope of dust with spherical symmetry DUSTY
code (Ivezic et al.)
Stellar input parameters distance 2 kpc V
10.1 Av 5.9 ? V0 4.2 Teff 20000 K log L/L?
5.6 R 53R? ? angular diameter Ø 0.25 mas
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Spherical model (DUSTY code) silicate with
large grains
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Spherical model (DUSTY code) silicate with
large grains
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Spherical model (DUSTY code) graphite with
large grains
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Spherical model (DUSTY code) graphite with
large grains
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Dust close to the star ?
SED can be reproduced by the spherical dust
model, but not the visibilities ? inner dust
radius is too large (12 mas for silicates and
60 mas for graphite) ! What is the origin of
the mid-IR emission relatively close to the star
measured with VLTI-MIDI ? Possibility to get
dust closer to the star Dense equatorial wind ?
disk-like structure able to shield the disk
material to allow molecules and dust to be formed
near the hot central star (Kraus Lamers 2003).
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Support for a non-spherical envelope

• A spherical model does not seem to simultaneously
  fit the SED and VLTI-MIDI visibilities
• Winds of sgBe have two components (e.g.
  Zickgraf et al. 1985)
• Several sgBe show high intrinsic polarizations
  consistent with non-spherical dusty envelopes
  (e.g. Magalhães 1992)

Zickgraf et al. (1985)
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Polarization PA versus VLTI-MIDI PA
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VLTI-AMBER observations
Equivalent uniform disc model V(l) 2J1(z) /
z , where z p qUD(l) Bproj / l
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VLTI-AMBER observations
UD diameter versus Position Angle
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VLTI-AMBER fit of V with gaussian-models
Chromatic variation of the major axis FWHM
2a2a0K(?-?0)C exp-4ln2(?- ?c)/??
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VLTI-AMBER closure phase
closure phase (deg)
Centrally-symmetric intensity distribution
l (microns)
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VLTI-AMBER differential phases
UT2-UT3
UT4-UT2
Differential phase
Differential phase
l (microns)
UT3-UT4
VLTI
Differential phase
No chromatic variation of objects symmetry
l (microns)
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Measured sizes of CPD-57 2874
AMBER
MIDI
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FIN THE END FIM ENDE
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Interstellar polarization ?
Stars within 2 of CPD-57 2874 (Heiles
2000) Stars with low and high polarizations
have random PA
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Modelling VLTI-MIDI observations
Inner radius
Silicate rin12 mas 100R 24 AU
Graphite rin60 mas 480R 120 AU
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Theory of (anisotropic) winds of massive stars
Maeder Desjacques (2001 AA), Lamers
Pauldrach (1991 AA), Maeder (1999 AA), Langer
et al. (1999 ApJ), etc