Linear spectropolarimetry

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Linear spectropolarimetry

• Jorick Vink (Armagh Observatory)

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Linear Spectropolarimetry

• PART I massive OB stars
• Wolf-Rayet stars (WRs)
• Luminous Blue Variables (LBVs)
• PART II pre-main sequence (PMS)
• Herbig AeBe stars
• T Tauri stars

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Part I (Outline)

• Massive star evolution
• Spherical winds?
• Linear polarimetry
• WR data
• LBV data

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Evolution of a Massive Star
O
O?LBV? WR ?SN
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Radiation-driven wind by Lines
Abbott Lucy (1985)

• dM/dt f (Z, L, M, Teff)

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Wind momenta at low Z
VLT FLAMES
Data (Mokiem)
Models (Vink)
Vink et al. (2001) Mokiem et al.
(2007)
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WR stars produce Carbon !
Geneva models (Maeder Meynet 1987)
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WR stars produce Carbon !
Geneva models (Maeder Meynet 1987)
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Which element drives WR winds?

• - C ? Mdot does not depend on host Z
• - Fe ? Mass loss DOES depend on host Z

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Z-dependence of WR winds
Vink de Koter (2005, AA)
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Implications of lower WR mass loss

• ? less angular momentum loss
• ? Long-duration GRBs favoured at low Z

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Are low Z WRs fast rotators?

• No v sin i
• Are the winds aspherical?
• ? Linear Polarimetry

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Polarimetry asymmetry
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No Polarisation
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Depolarisation
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LMC WR spectropolarimetry
VLT/FORS1 (Vink 2007)
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LMC WR spectropolarimetry
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Statistics

• Be stars in galaxy 60 line effects
• WR stars in galaxy 15-20
• WR stars in LMC 2/13 i.e. 15

(Poekert Marlborough 1976)
(Harries et al. 1998)
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Low Z Wolf-Rayet stars

• LMC WR winds as symmetric as galactic ones
• LMC winds strong enough to remove angular
  momentum
• GRB threshold Z 40 solar or less

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LBV Eta Car
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AG Car data
Text
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Linear polarisation from a disk
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Polarisation due to clumps
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PART II
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Part II PMS (Outline)

• Introduction
• T Tauri 1 Msun
• Herbig Ae 3 Msun
• Herbig Be 10 Msun
• Polarisation data
• Disc scattering models
• inner hole
• undisrupted
• X ray emission

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Questions for Star Formation

• Do all stars form by disk accretion?
• Is there a fundamental difference between low-
  and high mass star formation?

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Hertzsprung-Russell Diagram
Luminosity
ZAMS
F
K
M
O
B
A
G
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T Tauri stars Magnetospheric Accretion
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Intermediate mass Herbig stars

• Magnetic fields?
• Disks?
• YES Sub-mm
• (Mannings Sargent 1997)
• NO Infrared interferometry
• (Millan-Gabet et al. 2001)

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Polarisation across line?

1. No change
2. Depolarisation
3. LINE Polarisation

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No Polarisation
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Depolarisation
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Line Polarisation PA Flip
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Survey Herbigs and T Tauris

• Herbig Be stars 12
• Herbig Ae stars 11
• T Tauri stars 10

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Data Herbigs and T Tauris
PA
Pol
I
T Tauri
Herbig Be
Herbig Ae
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Polarisation across line?

1. No change
2. Depolarisation
3. LINE Polarisation

Herbig Be 7/12
Herbig Ae 9/11
T Tauri 9/10
(Vink et al. 2002, 2003, 2005b)
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QU Herbig Ae and T Tauri star
RY Tau
MWC 480
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Models of COMPACT line emission

• 3D Monte Carlo
• Keplerian rotating disk
• Flat or constant opening angle
• Scattering only no line transfer
• With and without an inner hole

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With/without an inner hole
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With/without a hole

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Constraining the inner disk radius
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Constraining the inner hole size

• Single PA flip known inclinations
• ? AB Aur Inner rim gt 5 Rstar
• ? CQ Tau Inner rim gt 4 Rstar
• ? SU Aur Inner rim gt 3 Rstar
• Gradual PA change
• ? GW Ori Inner rim 3 or 4 Rstar

(Vink et al. 2005a, 2005b)
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Imaged disks position angles
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Findings

• Herbig Be disks on small scales
• Herbig Ae/T Tau rotating accretion disks
• compact line emission
• inner holes
• sizes 3 5 stellar radii

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H-band image of MWC 297
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Chandra MWC 297 companion