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 O  LBV  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 OBA F G KM Luminosity 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 BeHerbig 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 angles

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