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Armando DOMICIANO de SOUZA
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)
Plan
Introduction
The B[e] 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
The B[e] 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
The B[e] phenomenon
(Lamers et al. 1998)
Supergiants B[e]  L*/Lsun > 104
Observations point
towards asymmetrical
stellar environments

Need for direct
measurements

High angular resolution
Zickgraf et al. (1985)
Principles of optical/IR
long baseline interferometry
IOTA spectro-interferometry
Bands J
H
K
Weigelt et al. (2003)
Principles of optical/IR
long baseline interferometry
Interference fringes
Intensity map I(y,z,l)
Weigelt et al. (2000)
GI2T - g Cas

Complex Visibilities
V(u,v,l)=
FT[I(u,v,l)] / FT[I(0,0,l)]
Interferometry : the uv or Fourier plane
ESO-VLTI
Intensity
distribution of
the object at
a given l
Complex
Visibility
V(u,v,l)
ASPRO - JMMC
Fourier
Transform
u and v  spatial frequency Bproj / l
Partial uv coverage

Models are needed to interpret the
current interferometric observations
Observations of B[e] stars with
VLTI-MIDI and VLTI-AMBER
Observational set-up:
MIDI
N band with R=30 (8-13 m)
Unit Telescopes (UTs)
2 baselines
AMBER
K band with R=1200 (2.1-2.2 m)
Unit Telescopes (UTs)
3 baselines (closure phase)
Targets:
GG Car
MIDI
Not well resolved
(size < 10 mas)
CPD-57 2874
MIDI and AMBER
VLTI-MIDI observations
MIDI
Equivalent uniform disc model:
V(l) = |2J1(z) / z| , where
z = p qUD(l) Bproj / l
VLTI-MIDI observations
UD diameter
versus
Position Angle
VLTI-MIDI : fit of V with gaussian-models
Chromatic variation of the major axis FWHM  2a = 2a0 + K (l-l0)
Gaussian
circle
2a = (8.70.4) + (2.20.3) (l-8m) mas
2a = (13.50.2) + (0.40.2) (l-12m) mas
Gaussian
ellipse
2a = (10.10.7) + (2.60.4) (l-8m) mas
Axial ratio 2b/2a = 0.76 0.08
Position angle PA = 144°  6°
2a = (15.30.7) + (0.50.2) (l-12m) mas
Axial ratio 2b/2a = 0.80 0.06
Position angle PA = 143°  6°
VLTI-MIDI spectrum
Possible origin of this featureless spectrum around 10 m:
Large grains ?
Carbonaceous dust ?
Free-free emission ?
Additional opacity sources ?
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
Spherical model (DUSTY code) :
silicate with large grains
Spherical model (DUSTY code) :
silicate with large grains
Spherical model (DUSTY code) :
graphite with large grains
Spherical model (DUSTY code) :
graphite with large grains
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).
Support for a non-spherical envelope
• A spherical model does not seem to simultaneously fit the SED and
VLTI-MIDI visibilities
• Winds of sgB[e] have two components (e.g. Zickgraf et al. 1985)
• Several sgB[e] show high intrinsic polarizations consistent with
non-spherical dusty envelopes (e.g. Magalhães 1992)
Zickgraf et al. (1985)
Polarization PA versus VLTI-MIDI PA
polarization <PA> = 45°3°
U
Data from Yudin & Evans (1998)
B
V
Yudin & Evans (1998)
Polarization perpendicular to disc:
(45°  3°) + 90°= 135  3°
N
Ellipse orientation from MIDI :
143.5°  6°
E
VLTI-AMBER observations
AMBER
Equivalent uniform disc model:
V(l) = |2J1(z) / z| , where
z = p qUD(l) Bproj / l
VLTI-AMBER observations
UD diameter
versus
Position Angle
VLTI-AMBER : fit of V with gaussian-models
Chromatic variation of the
major axis FWHM :
2a=2a0+K(l-l0)+C exp[-4ln2(l- lc)/l]
Gaussian
circle
2a = (2.460.01) + (5.20.1) (l-2.2m) mas
Brg  C = 0.640.08 mas ; l=1.6 0.2 pm
Gaussian
ellipse
2a = (3.900.03) + (7.30.2) (l-2.2m) mas
Axial ratio 2b/2a = 0.56 0.01
Position angle PA = -2.9°  0.4°
Brg  C = 0.930.11 mas ; l=1.6 0.2 10-3 m
closure phase (deg)
VLTI-AMBER : closure phase
VLTI
Centrally-symmetric
intensity distribution
l (microns)
Differential phase
UT2-UT3
Differential phase
Differential phase
VLTI-AMBER : differential phases
UT4-UT2
l (microns)
UT3-UT4
VLTI
No chromatic
variation of
object’s symmetry
l (microns)
Measured sizes of CPD-57 2874
AMBER
N
E
MIDI
FIN
THE END
FIM
ENDE
Interstellar polarization ?
Stars within 2° of
CPD-57 2874
(Heiles 2000)
Stars with low and
high polarizations
have random PA
Modelling VLTI-MIDI observations
Inner radius
Silicate
rin=12 mas ~100R* ~ 24 AU
Graphite
rin=60 mas ~480R* ~ 120 AU
Theory of (anisotropic) winds of massive stars
Maeder & Desjacques (2001 A&A),
Lamers & Pauldrach (1991 A&A),
Maeder (1999 A&A),
Langer et al. (1999 ApJ), etc
Rapid rotation and Log L/L > 104
 Star close to the -limit :
bi-stable winds
Lamers model
geff-effect
Eddington factor
variable in latitude
-effect
von Zeipel effect:
Maeder model
van Boekel (2003)
VLTI-VINCI
Mass loss variable in latitude (opacity and gravity effect) :
 Car