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Linear spectropolarimetry
Jorick Vink (Armagh Observatory)
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
Part I (Outline)
• Massive star evolution• Spherical winds?• Linear polarimetry• WR data• LBV data
Evolution of a Massive Star
O
OLBV WR SN
Radiation-driven wind by Lines
dM/dt = f (Z, L, M, Teff)
Abbott & Lucy (1985)
Wind momenta at low Z
Vink et al. (2001) Mokiem et al. (2007)
Models (Vink)
Data (Mokiem)VLT FLAMES
WR stars produce Carbon !
Geneva models (Maeder & Meynet 1987)
WR stars produce Carbon !
Geneva models (Maeder & Meynet 1987)
Which element drives WR winds?
- C Mdot does not depend on host Z
- Fe Mass loss DOES depend on host Z
Z-dependence of WR winds
Vink & de Koter (2005, A&A)
Implications of lower WR mass loss:
less angular momentum loss
Long-duration GRBs favoured at low Z
Are low Z WRs fast rotators?
• No v sin i
• Are the winds aspherical?
Linear Polarimetry
Polarimetry – asymmetry
No Polarisation
Depolarisation
LMC WR spectropolarimetry
VLT/FORS1(Vink 2007)
LMC WR spectropolarimetry
Statistics
• Be stars in galaxy: 60% line effects
• WR stars in galaxy 15-20%
• WR stars in LMC: 2/13 i.e. 15%
(Harries et al. 1998)
(Poekert & Marlborough 1976)
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
LBV: Eta Car
LBV spectropolarimetry
Text
(Davies, Oudmaijer & Vink, 2005)
AG Car data
Text
Linear polarisation from a disk
Q
U
Polarisation due to clumps
Q
U
PART II
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
Questions for Star Formation
• Do all stars form by disk accretion?
• Is there a fundamental difference between low- and high mass star formation?
Hertzsprung-Russell Diagram
O B A F G K M
Lum
inos
ity
T Tauri
Herbig AeBe
O stars
ZAMS
T Tauri stars: Magnetospheric Accretion
Intermediate mass: Herbig stars
• Magnetic fields?• Disks? YES – Sub-mm (Mannings & Sargent 1997)
NO – Infrared interferometry (Millan-Gabet et al. 2001)
Polarisation across line?
1. No change
2. Depolarisation
3. LINE Polarisation
No Polarisation
Depolarisation
Line Polarisation – PA Flip
Survey Herbigs and T Tauris
• Herbig Be stars: 12• Herbig Ae stars: 11• T Tauri stars: 10
Data: Herbigs and T Tauris
T TauriHerbig Be Herbig Ae
PA
Pol
I
Polarisation across line?
1. No change
2. Depolarisation
3. LINE Polarisation
Herbig Be: 7/12
Herbig Ae: 9/11
(Vink et al. 2002, 2003, 2005b)
T Tauri: 9/10
QU: Herbig Ae and T Tauri star
MWC 480 RY Tau
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
With/without an inner hole
With/without a hole
Constraining the inner disk radius
Constraining the inner hole size:
Single PA flip; known inclinations
AB Aur Inner rim > 5 Rstar
CQ Tau Inner rim > 4 Rstar
SU Aur Inner rim > 3 Rstar
Gradual PA change
GW Ori Inner rim 3 or 4 Rstar
(Vink et al. 2005a, 2005b)
McLean effect in FU Ori
PA
Pol
I
Accurate measurement of intrinsic polarisation PA
Imaged disks: position anglesPA line pol PA direct Delta PA
AB Aur 160 60/80 80/100
MWC 480 55 150 95
CQ Tau 20 105 95
RY Tau 163 62 101
FU Ori 45 47 2
SU Aur 130 127 3
DR Tau 120 128 8
Findings
• Herbig Be: disks on small scales
• Herbig Ae/T Tau: rotating accretion disks• compact line emission• inner holes• sizes 3 – 5 stellar radii
H-band image of MWC 297
Chandra: MWC 297 companion