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

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 Pb O´Toole & Heber 2006 CPD-64 461 207 207 PB/ 208 PB =solar

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 Convection He/H=1 sdO 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 parameters for >200 sdB atmospheric parameters for 130 sdO

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

10. Fits of SDSS-spectra: sdO sdOHe sdO

11. SPY: C & N lines solar - 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

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

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

14. solar SPY He-poor He-rich

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

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

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

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

19. Delayed helium shell flash He sdO

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

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

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

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

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

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

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 Masses: 0.45 to 0.55 M sun Envelope masses: 10 -3.... 10 -5 M sun sdB

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 all helium-rich - In none of the helium-poor ones (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 T eff = 45500K, log g = 5.23, mass = 0.5 M o 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 Vrad=700Km/s Hypervelocity star

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 sdO He sdO solar  sdB stars: - 2 sequences  sdO stars: - Spread by 6 orders of magnitude - 1/3 helium- deficient!

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

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

51. sdB = Extreme HB stars Saffer et al. 1994 EHB Post-EHB

52. The lower sequence Tracks from Driebe et al. (1998) M core

53. sdB and sdO stars from SPY SPY: ESO-VLT+UVES: High-res. Spectra of >1000 Double degenerate candidates - sdB: 79 (Lisker et al. 2005) - He-sdO: 30 (Ströer et al. sdO: 28 2007) - fraction of RV variables (P<10d): sdB: 39% He-sdO: 4% (1 SB2 binary) sdB

54. Trends and Sequences

55. Combining all studies Neglecting selection bias SDSS sdBs: To be done sdB Gap ? SPY-sds: no error bars shown

56. BPS Han et al: Binary population synthesis a)Without GK selection b)With GK selection

57. M 15 UV

58. Post EHB & post-AGB evolution Post-AGB Post EHB

59. UV spectroscopy of HB stars Caloi, Castellani et al. 1986 Heber et al. 1986 IUE

60. SDSS-sdOs Atmospheric models: - NLTE: - H+He, no metals - PRO2 code (Dreizler &Werner) - improved He atomic models - temperature correction scheme (Dreizler, 2003) sdO He sdO

61. Globular Cluster CMDs Moehler (2000) NGC 2808 (Walker, 1999) Blue hoo k

64. NGC 6752: HB &EHB stars Moni-Bidin et al. (2007) LTE spectral analyses: T eff, logg g match (E)HB prediction Helium subsolar

65. EHB Models Castellani et al. 1994 Helium core mass: 0.47 M sun depen- ding on He and metal abundance (fixed by onset of He core flash) Horizontal Branch= sequence of envelope mass M env, EHB=very low M env (0.01 M sun ), inert H-rich envelope avoids AGB evolutions

66. Origin of EHB stars Castellani & Castellani 1993 M=0.8 Msun η=0.75 EHB-progenitor stars must loose almost their entire envelope by the time of the helium core flash strong RGB mass loss; Low mass stars (Pop. II, globular cluster): Very efficient RGB Reimers wind may be sufficient. Younger populations, i.e. more massive progenitors (field): ?

67. KPD 1930+2752: sdB + massive WD Billeres et al, 2000 Maxted et al. 2000, Geier et al. 2007

68. Candidate SN Ia Progenitor KPD 1930+2752: Total mass=1.4 Msun (Chandrasekhar mass) -Double degenerate -System merges within 2 10 8 years -SN Ia explosion? (Geier et al. 2007) More on massive compaions: talk by Stephan Geier

69. sdB Asteroseismology Non-radial p-mode Pulsationa driven by Iron opacity bump: Predicted instability Strip matches Observations Charpinet et al. (2001)

70. sdB Asteroseismology Period matching technique: Linear theory: Amplitudes can not be predicted (PG1325+, Charpinet et al. 2006)

71. Metal abundances: Fe & Ni Feige 34: He-poor sdO Teff=60kK Fe/H=10*solarN i/H=70*solar

72. sdB Asteroseismology (PG1325, Charpinet et al. 2006) Model parameters: T eff, log g, M total, M env

73. sdB Asteroseismology PG 1605+072: Time resolved spectroscopy (9000 spectra) Radial velocity variations (O´Toole et al. 2005): 20 periods (few km/s) Line profile variations (phase folded, Tillich et al. 2007):

74. sdB Asteroseismology Dominant mode: Teff semi-amplitude: 800K Log gsemi-amplitude: 0.08 First harmonic detected Cleaning for dominant mode: 8 weaker modes detected

75. sdO stars from SDSS candidates selected from all releases according to colour: u-g<0.2 (0.4) g-r<0.1  11000 spectra:  40 sdO + 43 He sdO (Hirsch, Dipl. Thesis) Fits with NLTE models He sdO

76. The two sequences

77. Tracks from Dorman et al. (2003) with Z=0.02

78. The upper sequence Tracks from Dorman et al. (2003)

79. The lower sequence Tracks from Dorman et al. (2003)

80. Early NLTE Analyses : sdO Classification: He II > He I He-sdO: no Balmer detectable to the eye C and/or N strong sdO: otherwise Hunger et al. 1980 Heber (1987) Post-EHB Post-AGB

81. Evolution of hot subluminous stars: the canonical picture SdB + sdO stars: Extreme Horizontal Branch stars EHB HB sdB sdO Dorman et al. (1993, ApJ 419, 596)

82. He-rich sdOs: - diamonds: C&N strong - C strong triangles -N strong - (triangles)

83. The lower sequence Tracks from Driebe et al. (1998) M core