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