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Eta Carinae: Clues to Its Binarity

Eta Carinae: Clues to Its Binarity. Ted Gull. Krister Nielsen* Mike Corcoran John Hillier Kenji 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

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Eta Carinae: Clues to Its Binarity

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  1. Eta Carinae: Clues to Its Binarity Ted Gull Krister Nielsen* Mike Corcoran John Hillier Kenji Hamaguchi Stefan Ivarsson Gerd Weigelt* & AMBER Team * Lead authors in prep

  2. 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

  3. h 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

  4. Periodic Variability implies Binarity: • Damineli (1996) noted spectroscopic 5.52-year periodicity • Confirmed in X-rays, IR, visible, UV in 1998.0 • Coordinated observations of 2003.5 minimum • RXTE period 2024+-2 days (M. Corcoran 2005) • GTO (Gull), GO and Hubble Treasury (Davidson) monitoring • FUSE (fuv dropped during minimum), CHANDRA (dropped to few % during minimum), VLT/UVES + STIS (echelle disp1175- 10300A) • Much being learned about properties of ejecta • Homunculus: -513 km/s Fe I, V II, Ti II @ 760K H2 photoexcited during max, CH, OH, NH, CH+ 60K • Little Homunculus: -146 km/s Fe II, Cr II @ 6400K --> 5000K minimum • Strontium filament : Neutral emission region excited by Balmer continuum

  5. 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 h Car and Weigelt Blobs Weigelt blob excitation requires UV flux of 37,000K Companion (Eta B) Verner, Bruhweiler, Gull 2005 Smith et al 2005 ApJ Weigelt et al 1995 RMxAC

  6. P Cygni Absorption not present in Weigelt D except during periastron Balmer alpha changes: periastron to apastron Red=Periastron Blue=Near-Apastron Eta Carinae Weigelt D (D) _ D D Periastron: 1998.2 Near-Apastron: 2000.2 h _ D

  7. He I lines blueshifted relative to H I wind linesHe I linesappear to have narrow substructure for most of period H I 4103 He I 7065

  8. He I l7065 H I l4013 H I 4103, He I 7065, Fe II 5170, [N II] 5756 comparison

  9. STIS Radial 1998.0-2004.3 H I Absorption Velocities Curves derived from: 9 H I Balmer, Paschen lines 4 He I: 2 singlet & 2 triplet He I Absorption RXTE X-ray flux

  10. Geometry of Wind Interactions Gas pileup from primary wind 15000K 500 km/s 3x10-4Mo/yr 37000K 3000km/s 10-5Mo /yr Primary wind envelopes most of binary system, except dynamic cavity carved out by secondary wind.

  11. 2-D model of wind-windInterface in orbital plane. Pittard & Corcoran: D=30 AU, e=0.9

  12. VLTI/AMBER R=1500 R=1500 Weigelt et al. In prep. ~ 5 mas H I Br g He I 21S - 21P R= 10,000 R= 1500

  13. VLTI/AMBER R=1500 R=1500 IR Cont: 4 mas H I: 4-6 X centered on continuum He I emis~3X; offset? He I absor: ~4 mas

  14. Conclusion/ Frustration Velocity curve does not (easily) provide mass ratio. 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 • Apastron: March 2006 VLTI/AMBER observations: We look for • Eta B in continuum ~2% flux of Eta A ~8 mas PA~135o; • He I emission velocity components along wind-wind interface • Issue: sufficient UV-plane sampling?

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