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Recent results from the SIMECA code and the VLTI observations

Recent results from the SIMECA code and the VLTI observations. Anthony Meilland and Philippe Stee Observatoire de la Côte d’Azur. I. Active Hot Stars II. The SIMECA Code III. Modelling The VLTI data α Ara with MIDI α Ara with AMBER MWC297 with AMBER HD50013 with AMBER IV. Conclusion.

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Recent results from the SIMECA code and the VLTI observations

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  1. Recent results from the SIMECA code and the VLTI observations Anthony Meilland and Philippe SteeObservatoire de la Côte d’Azur

  2. I. Active Hot Stars II. The SIMECA Code III. Modelling The VLTI data α Ara with MIDI α Ara with AMBER MWC297 with AMBER HD50013 with AMBER IV. Conclusion

  3. I. Active Hot Stars What Are Active Hot Stars ? -Hot : Spectral Type O B A  Teff > 8000 K -Active : Emission lines, IR excess ,Envelope or disc, gaz or\and dust, Pulsations and other Variability

  4. I. Active Hot Stars A huge variety of phenomena ! -Fast Rotation : 60-80% of the critical velocity (nearly 100% for Achernar) -Stellar Wind : Radiatively driven, with high velocity -Binarity : Interaction with a companion, mass transfer -Pulsation : Non radial, many modes measured -Magnetism : few hundred Gauss recently measured

  5. I. Active Hot Stars A huge variety of geometry and Kinematics ! -Envelope shape : Spherical, flattened, thick or thin disc, ring, jets -Opacity : optically thin, thick or between -Inhomogeneities : outbursts, blobs, arms, holes … -Rotation law : Keplerian, angular momentum conservation … -Radial velocity : None, expansion, accretion or both … -Polar component of the velocity : Wind Compressed disc

  6. I. Active Hot Stars A huge variety of stars ! • -Be : Main sequence stars, ionised hydrogen disc, stellar wind • Herbig Ae\Be : Young stars, dust accretion disc, stellar wind • B[e] : super-giant stars, stellar wind, dust disc • Wolf Rayet : Strong mass loss, No photospheric line (optical thick wind) • …And even some more violent objects like the monster Eta Car !!

  7. II. The SIMECA code SIMulation d’Etoiles Chaudes Active Developed by Stee (1995) Stee and Bittar (2001) Stee and Meilland (2004) A physical model : Hydrodynamics (CAK wind model) and radiative transfer (in Sobolev approximation) in a rotating and expanding gaz envelope Made for interpretation of observations : Compute photometric (SED), spectroscopic (line profiles) and interferometric (intensity mapsvisibility curves) observables

  8. II. The SIMECA code Star and envelope physical parameters : Temperature Equatorial terminal velocity Stellar radius Polar terminal velocity Photospheric density Polar mass flux Rotational velocity Equatorial/polar mass flux ratio Inclination H/H+He “Free parameters” m1: Exponent of the mass flux variation law m2: Exponent of the velocity variation law Enter parameters :

  9. II. The SIMECA code Starting with the basic hydrodynamic equations : -Continuity equation -Mass conservation equation -No energy conservation (we don’t know the heating processes) -Perfect gaz equation With few hypothesis : -axial symmetry (no azimuthal dependency) -Stationarity -Temperature depending only on r -No polar component of the velocity in the envelope We obtain in the envelope the distribution of : : -Density -Radial and azimuthal velocity -Temperature Enter parameters : Hydrodynamic : ρ, Vr, VФ, T

  10. II. The SIMECA code We start with at the LTE (Level 1 to 7 + continuum) Using the Sobolev approximation (high velocity gradient) we obtain the statistic equilibrium equation : Aik, Bic et Ci : absorption, spontaneous emission and recombination coefficient βik : Escape probability (depend on the velocity gradient) We calculate the level population from this equations and the previous calculated values.. We iterate until the convergence of the values of the ni Enter parameters : Hydrodynamic : ρ, Vr, VФ, T Statistic equilibrium: n1,…,n7,ne at LTE n1,…,n7,ne non-LTE

  11. II. The SIMECA code Radiative transfer equation : τ calculated by integration: dτ =-κ . dz (along the line of sight ) In the Continuum : -Opacity of the envelope : Free-Free emission and electronic diffusion -Emissivity of the envelope : Free-Free and Free-Bound In the Lines : - κ and ε expression for the selected transition -Sobolev approximation Intensity function of the spatial variables (perpendicularly to the line of sight) for a transition (line) or function to the wavelength (continuum) Enter parameters : Hydrodynamic : ρ, Vr, VФ, T Statistic equilibrium: n1,…,n7,ne at LTE n1,…,n7,ne non-LTE Transfer equation in the contiuum Transfer equation In the lines Transfer equation In the continuum

  12. II. The SIMECA code In the line : Calculation of the zone of projected iso-velocity  Doppler shift -Spatial integration Line profile -Spectral integration (with a given spectral band) Intensity maps in the line In the continuum : -Spatial integration Spectral Energy Distribution -Spectral integration Intensity maps in the continuum Enter parameters : Hydrodynamic : ρ, Vr, VФ, T Statistic equilibrium: n1,…,n7,ne at LTE n1,…,n7,ne non-LTE Transfer equation in the contiuum Transfer equation In the lines Transfer equation In the continuum Spectral Energy Distribution Line Profiles Intensity maps in the continuum Intensity maps In the lines

  13. II. The SIMECA code Enter parameters : Hydrodynamic : ρ, Vr, VФ, T Statistic equilibrium: n1,…,n7,ne at LTE n1,…,n7,ne non-LTE Transfer equation in the contiuum Transfer equation In the lines Transfer equation In the continuum Spectral Energy Distribution Line Profiles Maps in the continuum Maps In the lines

  14. II. The SIMECA code Actual and Future developments • Actual : • -More levels for the free-bound emission (for MIDI data) • Ring and truncated disc model (evolution of the envelope) • -Interfacing with an accretion disc model (opacity of the dust) • -Asymmetry in the envelope Future : -Radiative transfer without Sobolev approximation (with Daniela Korkacova code) -Asymmetry in the envelope (Real 3D code without axisymmetry) -Real dynamics

  15. III. Modelling the VLTI data The VLTI 4 Telescopes: UT Fixed D=8,2m 4 Auxiliary Telescopes AT moveables D=1,6m - Baseline from few meters up to 200 m - Good (u,v) plane coverage (if you manage to have time and telescopes!!) Two Instruments MIDI AMBER Mid-infrared ( 2 spectral bandwidths ) 8-13 mm and 13-26 mm 2 telescopes Visibility modulus and differential phase Low spectral resolution ( R≈200) Maximum spatial resolution of 12 mas @ 10 μm Be studies: - Observation of a Ara during SDT ( June 2003) with HD 316285 (N=9.2, unresolved) and d Cen (N=15, unresolved) in June 2004 with UT1-UT3 B =103m) • Near infrared • 1-2.5 mm • 3 telescopes • Visibility modulus, differential phase, phase closure • Spectral resolution : R = 10000 • Maximum spatial resolution of 2,5 mas @ 2 μm • Be studies : • - Specially designed for stellar envelopes • - Kinematics studies • - Numerous faint objects • Already guarantee time dedicated to Be stars

  16. III. Modelling the VLTI data α Ara with MIDI Published In A&A in 2005 “First VLTI\MIDI observation of a Be star : α Arae” Chesneau, Meilland, Rivinius, Stee et al. B3Vne mV=2.8 mK=3.8 Teff = 18000 K R* = 4.8 Ro M* = 9.6 Mo Vsin i = 220km/s Distance : 74 pc Polarization : 172°

  17. III. Modelling the VLTI data α Ara with MIDI VLTI data obtained in June 2003 and Spectrum from Brazil in august 2003 Visibilities as a function of l (8-13.5 mm) : june, 16 : B=102 m , PA = 7° june, 17 : B=79 m , PA = 55° Spectral Energy Distribution : (8-13.5 mm) Pa b line profile: (1,28 mm, transition 5-3)

  18. III. Modelling the VLTI data α Ara with MIDI FEROS data obtained in may 1999 (Thomas Rivinius) (transition 2-3) (transition 2-4)

  19. III. Modelling the VLTI data α Ara with MIDI Hα EW variations between 1978 and 2003

  20. Circumstellar disk variations between 1999 & 2003 Continuum supposed constant between 1999 & 2003 Two groups from non simultaneous Spectroscopic and interferometric data May 1999 & Summer 2003 Fit of the Ha & Hb lines (1999) Few parameters variables: density, wind velocity, envelope extension Fit of the Paschen b (2003) Agreement between observed and simulated visibilities? Physical Parameters determination Ha line profile variation between 1978 & 1999 Timescale around 7 years

  21. α Ara’s SED

  22. Problem : Mismatch between the two ditances determination. Not possible for a B3Vne to have a radius less than 5 Ro Maybe a (unseen) companion can produce a wrong Hipparcos parallax or Error from Cohen et al. (2001) estimation Results α Ara’s distance From Hipparcos : 74 pc Parallax From Cohen et al. 2001 : 122 pc Fluxes & Color indices SIMECA : Flux depends on the star radius and distance (Radius used : 4.8 Ro) Distance obtained: 105 pc 74 pc 105 pc

  23. Input Parameters R*=5Ro Teff = 18000K rphot=1.2 10-12 Vphot = 0.08 Vrot = 300 km/s g = 0.86 fPole = 1.7 10-9 m1 = 0.3 m2 = 0.45 C1 = 30 Vpôle = 2000 km/s Veq = 180 km/s i = 45° Nearly spherical Inclination  Vrot Strong polar wind Low equatorial wind Ha & Hb fits

  24. Fit of the Paschen b line and visibilities Variations ? Envelope Geometry density Winds Flattening inhomogeneities Troncated disk Variations & parameters

  25. r decreases by 25% (rphot=0.97 10-12) Rmax decreases by 18% (Rmax = 82.7R*)

  26. Best Scenario: Disk troncature by a close companion a Ara’s Binarity = z tau ? Decrease of the envelope extension (4,5 times ≈ 22 R*) + Constant Flux (density increase) Period : 70 days Orbital radius : 32 R* Masse of the companion : <2Mo AMBER Observations : Pab & Brg Baseline : 20 up to 100 m Avoid P.A. ≈ 12° Problems with the visibilities fits

  27. III. Modelling the VLTI data α Ara with AMBER (Preliminary work) Amber Br γ line profile (not calibrated) This emission line is produced within the Circumstellar envelope

  28. III. Modelling the VLTI data α Ara with AMBER Theoretical visibilities using the SIMECA code AMBER visibility

  29. III. Modelling the VLTI data α Ara with AMBER Theoretical phase using the SIMECA code AMBER phase

  30. III. Modelling the VLTI data MWC297 with AMBER (work in progress) • MWC297 : • Herbig Be star • Strong hydrogen line in emission (Hα = 120 and Hβ=11) • Star + Accretion disc + Wind Accretion disc + Star: Code by Fabien Malbet Wind : Modified version of SIMECA ( with the opacity and emission from the accretion disc) • Data : • -Flux and visibility in the K band with Mid resolution • -Br γ line profile with quite high resolution (ISAAC) • Hα and Hβ line profile from Drew’s 1999 article • Magnitudes and ISO spectra

  31. III. Modelling the VLTI data MWC297 with AMBER • Problem : Where is the Wind ? • In the equatorial plan ? At the pole? Near the star ? • Quasi spherical wind, high velocity in the pole (600km\s), low velocity at the interface with the disc (70km\s) Br γ emission zone : starts at 8R ends at 50R 8 with a maximum around 27R

  32. III. Modelling the VLTI data MWC297 with AMBER Problem : Differences between the 3 studied lines Hα and Hβ profiles are very large (up to 600km\s) Br γ profile is quite narrow (less than 200km\s) They comes from slightly different regions

  33. III. Modelling the VLTI data MWC297 with AMBER

  34. III. Modelling the VLTI data HD50013 with AMBER (preliminary work) Flux from SIMBAD : Magnitudes U,B,V,R,I,J,H,K,L,M + UV Flux (0.2-0.4μm) + ISO Flux 10-30-60-100μm + Radio measurements Star : B1.5IVe = Planck function with : Teff =22500K Radius = 6 R Distance = 242 parsecs Classical Be star IR excess : Beginning at 2μm Spectral Energy Distribution (SED)

  35. III. Modelling the VLTI data HD50013 with AMBER Fit of the SED with the SIMECA code Total = Star + free-free + free-bound Star = Planck Free-Free and Free- Bound emission from the circumstellar envelope : Inclination = 45° Density at the photosphère = 10 -13 g.cm -3 Mass loss = 10-9 M\year

  36. III. Modelling the VLTI data HD50013 with AMBER Line profiles H H H Hydrogen (+ He and Fe) lines in emission = Circumstellar matter H  H FeII l 5317 A HeI l 5876 A Dachs et al. 1992, A&AS, 95, 437 Asymmetric profiles Wine bottle or double peaks Long-term variations From Lenorzer A. et al. 2002, A&A, 384, 473 Slettebak et al. 1992 ApJ Supp. 81, 335

  37. III. Modelling the VLTI data HD50013 with AMBER Spectrum Visibility Modulus Differential phase Closure phase

  38. III. Modelling the VLTI data HD50013 with AMBER Visibility Modulus HD 50013 SIMECA simulation for a classical Be star Asymmetric Visibility modulus variation in the Br γ line = Red part of the emission in the line is more resolved than in the continuum, but blue part is less resolved = Inhomogeneity in a rotating envelope (cf “one-armed oscillations Berio et al. 1999) ? = Need of an asymmetric model Visibility variation in the line (Hα) for a classical Be star for different rotational velocity law (Constant, keplerian, angluar momentum conservation…)

  39. III. Modelling the VLTI data HD50013 with AMBER Visibility Phase HD 50013 SIMECA simulation for a classical Be star No phase variation in the Br γ line = Circumstellar matter dominated by radial movement = No Rotation ? ! Phase variation in the line (Hα) for different rotational velocity law (Constant, keplerian, angluar momentum conservation…)

  40. IV. Conclusion • Need of lot of data to constrain models: • Simultaneous and time series with various timescales • each kind of data constrains some parameters • photometric  density, mass flux (and star parameters) • interferometric  geometry (+ kinematics if differential) • spectroscopic  kinematics ( + geometry ) • Need of two kind of model : • Physical but simple enough to be fast = SIMECA • + non-axisymmetric + dynamics (for inhomogeneity) • More complex with less approximations (Sobolev) • to test the limits of the SIMECA code •  Slower  can’t be use easily to model observations

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