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U li Heber

U li Heber. Subluminous O stars Origin and evolutionary links. Hydrogen-Deficient Stars, Tübingen 20.9.2007. Outline. Early results Atmospheric parameters Evolutionary scenarios - Close binary evolution (RLOF, CEE & WD mergers) vs - Delayed core helium flashers

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U li Heber

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  1. Uli Heber Subluminous O stars Origin and evolutionary links Hydrogen-Deficient Stars, Tübingen 20.9.2007

  2. Outline • Early results • Atmospheric parameters • Evolutionary scenarios - Close binary evolution(RLOF, CEE & WD mergers) vs - Delayed core helium flashers - (non-core helium-burning stars) • Kinematics • Summary & Outlook

  3. sdO vs. sdB stars • sdO stars: • - H-deficient • Hot > 40kK • He-sdOs: • No hydrogen sdO sdB sdB stars: - helium-deficient - „cool“: 20-40kK

  4. Subluminous O and B stars Greenstein & Sargent (1974)

  5. sdB stars:He-deficiency from diffusion Metal abundances HST/STIS UV spectra • Enrichment of heavy elements (>100 times) except Fe • Radiative levitation Fe CPD-64 461 207 207PB/208PB =solar Pb O´Toole & Heber 2006

  6. Post-EHB vs post-AGB evolution sdB = Extended Horizontal Branch stars: - He-burning core & inert H-envelope (<0.01 Msun) - How to loose the envelope? - sdO stars=post-EHB? • Post-AGB Objects: • rare • linked to RCrB/EHe stars

  7. sdB sdO Convective transformation (Wesemael et al. 1982) Groth et al. (1985): Convection occurs in He-rich atmo- spheres only sdO Convection He/H=1 sdB

  8. Hot subdwarfs from UVX Surveys LTE- spectroscopic analyses of sdB stars: - Palomar Green survey: Saffer et al. 1994, Maxted et al. 2000 - Hamburg Quasar Survey: Edelmann et al. 2003 - ESO-Supernova Progenitor Survey (SPY): Lisker et al. 2005 NLTE spectroscopic analyses of sdO-stars: - SPY (Ströer et al. 2007) - Sloan Digital Sky Survey (Hirsch et al. 2007) atmospheric parametersfor >200 sdB atmospheric parameters for 130 sdO

  9. Fits of UVES-spectra (SPY): sdO high resolution spectra, UVES@VLT, TMAP NLTE models, H&He only sdO He sdO

  10. Fits of SDSS-spectra: sdO sdO He sdO

  11. SPY:C & N lines • - C&N strong: • diamonds • C strong: • triangle • N strong • - no C or N: open • - All He-rich sdOs • have C and/or N • None of the • He-poor have C/N solar solar

  12. Carbon III/IV SPY: n(C)=0.13% (Hirsch et al. 2007) vrot sin i=0 km/s

  13. Carbon III/IV SPY: n(C)=0.25% (Hirsch et al. 2007) vrot sin i=20 km/s

  14. SPY He-rich He-poor solar

  15. The canonical picture • Smooth evolutionary • time scales: • He-poor scattered in diagram • progeny of sdB stars • Clumping of He-rich sdOs • can not be explained He-ZAMS

  16. SPY&SDSS: sdB,sdO & He-sdO sdO stars: He-sdO: clumping at • Teff = 45000K • log g = 5.8 He-sdO clump sdB SPY-sds: without error bars

  17. SPY&SDSS: sdB,sdO & He-sdO Post EHB He-ZAMS EHB Sub- He-ZAMS

  18. Hot He flashers Core flash Delayed He core flash Core flash Canonical evolution Sweigart, 1987

  19. Delayed helium shell flash He sdO

  20. Very late helium core flash He sdO Could explain He-sdOs below the Helium ZAMS He/C

  21. sds in binaries SPY: fraction of close binaries: radial velocity variables with P<10d sdBs; :40% (Napiwotzki et al.,2005) sdOs:4% RVV (from SPY) • mostly single-lined: RV curve:mass function Minimum mass of companion Napiwotzki et al. 2007

  22. Period distribution Nature of companions: white dwarf or low mass m.s. stars Morales-Rueda (2006) MS unknown WD

  23. Binary Population Synthesis (BPS) Han et al. (2003) a: 1. CE ejection b: 1. stable RLOF c: 2. CE ejection d: merger of two helium white dwarfs

  24. Comparison to Han et al. (HPMM) sdBs: best match: models with correlated masses and low CEE efficiency Poor match: models with 100% CEE efficiency O-types: He-rich sdOs: stars clump at 45000K, too hot for any HPMM simulation set He-poor sdO: scattered in (Teff, log g) diagram Ströer et al. 2007

  25. Non core helium-burning evolution Star leaves RGB Before helium ignites in the core (e.g. by mass tranfer to a companion) Cooling tracks to form helium white dwarfs M=0.8 Msun η=0.75 Castellani, Castellani & Moroni (2006)

  26. Non-core helium-burning sdB stars HD 188112 (V=10.2) (Heber et al., 2001) - Hipparcos parallax - distance = 80 pc - mass = 0.22 Msun No helium burning - companion: M>0.72Msun Tracks: Driebe et al.

  27. A Hyper-velocity star (HVS) amongst sdO stars from SDSS Galactic restframe velocity HVS -500 0 +500 km/s

  28. SMBH Slingshot Hills (1988): • Disruption of a binary near a Super-Massive Black Hole releases companion at up to 1000 km/s or more. • Detection of a single HVS: evidence for a SMBH Gualandris et al. (2005)

  29. Summary& Conclusion • Origin of sdB/sdO stars? (i) delayed core helium flash (ii) close binary evolution (RLOF & CEE ejection), mergers of He-WDs • He-poor sdOs are the progeny of sdB stars • He-rich sdO stars are hotter than predicted by (i) & (ii) atmospheres: No metal line blanketing metalicity effects evolution (Brown et al. 2007) • Post-AGB-evolution & Non-core He-burning evolution: rare due to short evolutionary time scales

  30. Outlook: A pulsating sdO star Strongest mode: P=119.3 s A=38.6 mmag plus - First Harmonic plus - 8 modes: 62 ... 118s Woudt et al. (2001)

  31. Stellar & Envelope Masses sdB Masses: 0.45 to 0.55 Msun Envelope masses: 10-3.... 10-5 Msun

  32. Thank You!

  33. sdB Asteroseismology Multi-periodic light variations (few mmag) at periods from 2 to 10min. Østensen et al. (2001)

  34. Carbon and Nitrogen SPY: C and/or N lines Detected - in allhelium-rich - Innone of the helium-poorones (Ströer et al. 2007)

  35. Carbon abundances

  36. Challenges • Observations: better statistics, better data: the quest for high resolution. metal abundances (see Poster 25) • Evolution theory: Prediction of surface abundances for late hot flasher (Cassisi et al. 2003) & He WD mergers • Angular momentum and stellar rotation • Stellar atmospheres & envelopes: diffusion (rad. levitation) & metal line blanketing, see talk by G. Michaud • Mass loss and diffusion • The role of magnetic fields (O´Toole et al. 2005)

  37. Grazie!

  38. Blue Hook stars

  39. HD128220B: Fe & Ni Fe/H=1/100 solar Ni/H=1/10 solar

  40. US 708: Keck LRIS spectrum • Teff = 45500K, • log g = 5.23, • mass = 0.5 Mo • B=19.0 mag • Distance: 19 kpc

  41. Run-away stars • Ejection scenario: born in the plane and ejected (Blaauw, 1961) - binary supernova ejection - 3 body interaction in an open cluster • Calculate path and time of flight: - radial velocities, distances & proper motion - orbit integrator: Odenkirchen & Brosche (1992) - Galactic potential: Allen & Santillan (1991)

  42. BD+75 325 (Lanz et al. 1997) - Slight enrichment of Fe&Ni • fully metal line blanketed models: Teff lower by 6000K than metal free models

  43. Metallicity effects on atmospheric parameters for the sdB SB 707 Solar ([m/H]=0.0): Teff = 33940K log g= 5.82 log He/H=-2.95 10*solar ([m/H]=+1.0) : Teff = 35380K log g= 5.90 log He/H=-2.91 Metal line blanketed LTE models

  44. Summary II Heavy metals in sdO and sdB stars: • Non solar abundances of Fe & Ni in sdO stars • Non solar Ni/Fe (>solar) • Strong enrichment of many iron group elements in hot sdB stars (except Fe), about solar in “cool” sdBs (<30000K): FUV flux suppression UV upturn • Teff scale significantly changed by supersolar metal abundances (line blanketing)

  45. Outlook: Radial velocities Hypervelocity star Vrad=700Km/s

  46. Cosmic accelerator? Ejection from a cluster by three body interaction? SN II in a binary release companion at orbital velocity? Supermassive black hole in the Galactic center? Better ideas??

  47. HQS-sdB: comparison with Han et al.

  48. Trends of helium abundance sdB He sdO • sdB stars: • - 2 sequences • sdO stars: • - Spread by • 6 orders of • magnitude • - 1/3 helium- • deficient! sdO solar

  49. sdB Helium abundances Edelmann et al. 2003 Two sequences: He/H vs. Teff

  50. Hamburger Quasar Survey sdB stars: Edelmann et al. 2003: 100 sdB stars

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