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Armando DOMICIANO de SOUZA

The vicinity of galactic supergiant B[e] stars from IR long baseline interferometry with the VLTI. Armando DOMICIANO de SOUZA.

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Armando DOMICIANO de SOUZA

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  1. The vicinity of galactic supergiant B[e] stars from IR long baseline interferometry with the VLTI 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)

  2. 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

  3. 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 opticalspectrum. 4. Astrong near or mid-infrared excess due to hot circumstellardust. Meilland

  4. Need for direct measurements  High angular resolution The B[e] phenomenon(Lamers et al. 1998) Supergiants B[e]  L*/Lsun > 104 Observations point towards asymmetrical stellar environments Zickgraf et al. (1985)

  5. IOTA spectro-interferometry Bands J H K Weigelt et al. (2003) Principles of optical/IR long baseline interferometry

  6. Complex Visibilities V(u,v,l)= FT[I(u,v,l)] / FT[I(0,0,l)] Intensity map I(y,z,l) Weigelt et al. (2000) GI2T - g Cas Principles of optical/IR long baseline interferometry Interference fringes 

  7. Intensity distribution of the object at a given l ESO-VLTI Fourier Transform Complex Visibility V(u,v,l) ASPRO - JMMC 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

  8. 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

  9. MIDI VLTI-MIDI observations Equivalent uniform disc model: V(l) = |2J1(z) / z| , where z = pqUD(l) Bproj / l

  10. VLTI-MIDI observations UD diameter versus Position Angle

  11. Gaussian circle 2a = (8.70.4) + (2.20.3) (-8m) mas 2a = (13.50.2) + (0.40.2) (-12m) mas Gaussian ellipse 2a = (10.10.7) + (2.60.4) (-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) (-12m) mas Axial ratio 2b/2a = 0.80 0.06 Position angle PA = 143°  6° VLTI-MIDI : fit of V with gaussian-modelsChromatic variation of the major axis FWHM 2a = 2a0 + K (-0)

  12. VLTI-MIDI spectrum Possible origin of this featureless spectrum around 10 m: Large grains ? Carbonaceous dust ? Free-free emission ? Additional opacity sources ?

  13. 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

  14. Spherical model (DUSTY code) : silicate with large grains

  15. Spherical model (DUSTY code) : silicate with large grains

  16. Spherical model (DUSTY code) : graphite with large grains

  17. Spherical model (DUSTY code) : graphite with large grains

  18. 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 tothe 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).

  19. 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)

  20. N E polarization <PA> = 45°3° Polarization perpendicular to disc: (45°  3°) + 90°= 135  3° Ellipse orientationfrom MIDI : 143.5°  6° U B V Data from Yudin & Evans (1998) Yudin & Evans (1998) Polarization PA versus VLTI-MIDI PA

  21. AMBER VLTI-AMBER observations Equivalent uniform disc model: V(l) = |2J1(z) / z| , where z = pqUD(l) Bproj / l

  22. VLTI-AMBER observations UD diameter versus Position Angle

  23. Gaussian circle 2a = (2.460.01) + (5.20.1) (-2.2m) mas Br C = 0.640.08 mas ; =1.6 0.2 pm Gaussian ellipse 2a = (3.900.03) + (7.30.2) (-2.2m) mas Axial ratio 2b/2a = 0.56 0.01 Position angle PA = -2.9°  0.4° Br C = 0.930.11 mas ; =1.6 0.2 10-3m VLTI-AMBER : fit of V with gaussian-models Chromatic variation of the major axis FWHM : 2a=2a0+K(-0)+C exp[-4ln2(- c)/]

  24. VLTI VLTI-AMBER : closure phase closure phase (deg) Centrally-symmetric intensity distribution l (microns)

  25. VLTI-AMBER : differential phases UT4-UT2 UT2-UT3 Differential phase Differential phase l (microns) UT3-UT4 VLTI Differential phase No chromatic variation of object’s symmetry l (microns)

  26. N E Measured sizes of CPD-57 2874 AMBER MIDI

  27. FIN THE END FIM ENDE

  28. Interstellar polarization ? Stars within 2° of CPD-57 2874 (Heiles 2000) Stars with low and high polarizations have random PA

  29. Modelling VLTI-MIDI observations Inner radius Silicate rin=12 mas ~100R* ~ 24 AU Graphite rin=60 mas ~480R* ~ 120 AU

  30. Theory of (anisotropic) winds of massive stars bi-stable winds von Zeipel effect: Lamers model geff-effect Rapid rotation and Log L/L > 104  Star close to the -limit : -effect Eddington factor variable in latitude Maeder model van Boekel (2003) VLTI-VINCI Mass loss variable in latitude (opacity and gravity effect) :  Car Maeder & Desjacques (2001 A&A), Lamers & Pauldrach (1991 A&A), Maeder (1999 A&A), Langer et al. (1999 ApJ), etc

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