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Eta Carinae: Clues to Its Binarity

Ted Gull

Krister Nielsen*Mike CorcoranJohn HillierKenji Hamaguchi Stefan Ivarsson

Gerd Weigelt*& AMBER Team

* Lead authors in prep

OUTLINE

•Brief background of Eta Carinae including periodicity•Binarity evidence from:

• Weigelt D STIS spectra•‘Stellar’ Line profiles

• A Simple model•VLTI/AMBER - first result•Visualization of wind structure

Car In late CNO cycle -- N overproduced at expense of C, O

•the Great Event in 1840s•-1 magnitude; bright for 20 years• > 12 Mo Ejected -> Homunculus

• another event in the 1890s•~> 0.5 Mo Ejected -> Little Homunculus

•Luminosity~ 5x106 Lo T e~15,000K ==>MASS>100 Mo

•Mass Loss Rate: ~10-3 Mo/yr•Wind Velocity: 500-600 km/s

•Historical spectrum highly variable

Periodic Variability implies Binarity:

Damineli (1996) noted spectroscopic 5.52-year periodicityConfirmed in X-rays, IR, visible, UV in 1998.0Coordinated observations of 2003.5 minimum

RXTE period 2024+-2 days (M. Corcoran 2005)

GTO (Gull), GO and Hubble Treasury (Davidson) monitoringFUSE (fuv dropped during minimum), CHANDRA (dropped to few % during

minimum), VLT/UVES + STIS (echelle disp 1175- 10300A)

Much being learned about properties of ejectaMuch being learned about properties of ejectaHomunculus: -513 km/s Fe I, V II, Ti II @ 760K HHomunculus: -513 km/s Fe I, V II, Ti II @ 760K H22 photoexcited during max, photoexcited during max, CH, OH, NH, CHCH, OH, NH, CH+ + 60K60KLittle Homunculus: -146 km/s Fe II, Cr II @ 6400K --> 5000K minimumLittle Homunculus: -146 km/s Fe II, Cr II @ 6400K --> 5000K minimumStrontium filament : Neutral emission region excited by Balmer continuumStrontium filament : Neutral emission region excited by Balmer continuum

•B, C and D are very bright emission clumps located to NE•Photoexcited by Eta A & Eta B•Projected distance: 300 - 600 AU•Proper motion, velocity suggest in skirt between lobes, tilted at 450 to skyplane

Car and Weigelt Blobs

Weigelt et al 1995 RMxACSmith et al 2005 ApJ

Weigelt blob excitation requires UV flux of 37,000K Companion (Eta B) Verner, Bruhweiler, Gull 2005

Balmer alpha changes: periastron to apastron

Periastron: 1998.2

Near-Apastron: 2000.2

Red=PeriastronBlue=Near-Apastron

Eta Carinae

Weigelt D (D)

_D

D

_D

P Cygni Absorption not present in Weigelt D except during periastron

He I lines blueshifted relative to H I wind linesHe I lines appear to have narrow substructure for most of period

He I 7065 H I 4103

H I 4103, He I 7065, Fe II 5170, [N II] 5756 comparison

He I 7065 H I 4013

STIS Radial 1998.0-2004.3

Curves derived from:

9 H I Balmer, Paschen lines

4 He I: 2 singlet & 2 triplet

RXTE X-ray flux

H I Absorption

He I Absorption

Velocities

Geometry of Wind Interactions

15000K500 km/s

3x10-4Mo/yr

37000K3000km/s10-5Mo /yr

Gas pileup from primary wind

Primary wind envelopes most of binary system, except dynamic cavity carved out by secondary wind.

2-D model of wind-windInterface in orbital plane.

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Pittard & Corcoran:

D=30 AU,

e=0.9

VLTI/AMBERWeigelt et al. In prep.

~ 5 mas

H I Br

He I 21S - 21P

R=10,000

R=

1500

R=1500 R=1500

VLTI/AMBER

IR Cont: 4 mas

H I: 4-6 X centered on continuum

He I emis~3X; offset?

He I absor: ~4 mas

R=1500 R=1500

Apastron: March 2006 VLTI/AMBER observations: We look for• Eta B in continuum ~2% flux of Eta A ~8 mas PA135o;• He I emission velocity components along wind-wind interface• Issue: sufficient UV-plane sampling?

Conclusion/ Frustration

STIS observations of H I, He I, Fe II ‘wind’ lines & Weigelt blobs consistent with hot binary companion blowing cavity in primary wind and He II ionization leading to He I recombination

Prediction: The Holy Grail --> Eta Car B

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Velocity curve does not (easily) provide mass ratio.