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SPETTROSCOPIA DI STELLE CALDE DI RAMO ORIZZONTALE IN AMMASSI GLOBULARI

SPETTROSCOPIA DI STELLE CALDE DI RAMO ORIZZONTALE IN AMMASSI GLOBULARI. COFIN 2001 – Bologna, 12 giugno 2003. Theoretical and observational framework. Same core mass (0.5 M  ) Different total mass. Horizontal Branch. HB morphology. Theoretical and observational framework.

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SPETTROSCOPIA DI STELLE CALDE DI RAMO ORIZZONTALE IN AMMASSI GLOBULARI

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  1. SPETTROSCOPIA DI STELLE CALDE DI RAMO ORIZZONTALE IN AMMASSI GLOBULARI COFIN 2001 – Bologna, 12 giugno 2003

  2. Theoretical and observational framework Same core mass (0.5 M) Different total mass. Horizontal Branch HB morphology

  3. Theoretical and observational framework Same core mass (0.5 M) Different total mass. •Stellar evolution: (internal structure) Blue tail • Possibly the prime contributors to the UV emission in elliptical galaxies. HB morphology • Population synthesis of extragalactic non resolved systems. • Star formation history modeling in dwarf galaxies of the Local Group.

  4. Theoretical and observational framework Blue Tails The most extreme espresion of the second parameter problem Why hot HB stars can loose so much mass? Menv< 0.2 M Temperatures up to ~ 35 000 K

  5. Theoretical and observational framework Blue Tails • Gaps: regions underpopulated in stars, which appear in the blue HB sequences of many globular clusters.

  6. Theoretical and observational framework Blue Tails • Gaps: regions underpopulated in stars, which appear in the blue HB sequences of many globular clusters. Piotto et al. (1999) Same mass

  7. Theoretical and observational framework Blue Tails Ferraro et al. (1998) Differences in: • Gaps: regions underpopulated in stars, which appear in the blue HB sequences of many globular clusters. Evolution Mass loss [CNO/Fe] He mixing Rotation Origin (binaries) Abundances Same mass or same temperature

  8. Theoretical and observational framework Blue Tails • Gaps: regions underpopulated in stars, which appear in the blue HB sequences of many globular clusters. Sweigart (2001) • Diffusive processes: Michaud, Vauclair & Vauclair (1983): •Radiative levitation of metals and gravitational settling of helium. • Atmosphere must be stable (non-convective and slowly rotating) to avoid re-mixing). Abundance anomalies

  9. Theoretical and observational framework Blue Tails • Gaps: regions underpopulated in stars, which appear in the blue HB sequences of many globular clusters. Sweigart (2001) • Diffusive processes: He Fe Mg Abundance anomalies Ti Si Ca P Cr CNO Behr et al. (2000)

  10. Theoretical and observational framework Blue Tails • Gaps: regions underpopulated in stars, which appear in the blue HB sequences of many globular clusters. • Diffusive processes: Abundance anomalies Low gravities •Moehler et al. (1995, 1997, 2000) •de Boer et al. (1995) •Crocker et al. (1998)

  11. Theoretical and observational framework Blue Tails • Gaps: regions underpopulated in stars, which appear in the blue HB sequences of many globular clusters. • Diffusive processes: Abundance anomalies Low gravities Luminosity jump Grundahl et al. (1999)

  12. Theoretical and observational framework Blue Tails • Gaps: regions underpopulated in stars, which appear in the blue HB sequences of many globular clusters. • Diffusive processes: Abundance anomalies Low gravities • Peterson et al. (1983-1995) : M3, M4, M5, M13, NGC 288, halo. • Cohen & McCarthy (1997) : M92 • Behr et al. (1999-2000) : M3, M13, M15, M68, M92, NGC 288. • Kinman et al. (2000) : metal-poor halo Luminosity jump • Fast rotation

  13. Theoretical and observational framework Blue Tails Many open questions on HB morphology and hot HB stars nature • Gaps: regions underpopulated in stars, which appear in the blue HB sequences of many globular clusters. The origine of blue tails: why hot HB stars loose so much mass? Is there any relation between fast rotation and HB morphology? • Diffusive processes: How is the distribution of stellar rotation along the HB? Abundance anomalies Low gravities Which is the origine of fast stellar rotation on HB stars? Luminosity jump • Fast rotation

  14. The spectroscopic approach Ultraviolet Visual Echelle Spectrograph (UVES) + VLT R ~ 40 000 => 0.1 Å (7.5 km/s) 3730 – 4990 Å

  15. The spectroscopic approach Ultraviolet Visual Echelle Spectrograph (UVES) + VLT Exposure times: 800s – 2.5 h/star 61 hot HB stars observed

  16. The spectroscopic approach Ultraviolet Visual Echelle Spectrograph (UVES) + VLT Exposure times: 800s – 2.5 h/star 61 hot HB stars observed

  17. The spectroscopic approach Ultraviolet Visual Echelle Spectrograph (UVES) + VLT Exposure times: 800s – 2.5 h/star 61 hot HB stars observed

  18. The spectroscopic approach ROTATIONAL VELOCITY Analysis procedure: Cross-correlation technique Projected rotational velocity (vsini) determined via the CCF (Tonry & Davis, 1979)using rotation standard stars of similar spectral type (Peterson et al. 1987). 2

  19. The spectroscopic approach ROTATIONAL VELOCITY Analysis procedure: Cross-correlation technique Projected rotational velocity (vsini) determined via the CCF (Tonry & Davis, 1979)using rotation standard stars of similar spectral type (Peterson et al. 1987). vsin i = A  - = A  2 2 o rot  2

  20. The spectroscopic approach ROTATIONAL VELOCITY Analysis procedure: Cross-correlation technique Projected rotational velocity (vsini) determined via the CCF (Tonry & Davis, 1979)using rotation standard stars of similar spectral type (Peterson et al. 1987). vsin i = A  - = A  2 2 o rot 2

  21. The spectroscopic approach ROTATIONAL VELOCITY 2

  22. The spectroscopic approach ROTATIONAL VELOCITY 2

  23. The spectroscopic approach ROTATIONAL VELOCITY 2

  24. The spectroscopic approach ROTATIONAL VELOCITY RESULTS Recio-Blanco et al., ApJL 572, 2002 • Fast HB rotation, although maybe not present in all clusters, is a fairly common feature. • The discontinuity in the rotation rate seems to coincide with the luminosity jump - All the stars with Teff>11 500 K have vsin i < 12 km/s - Stars with Teff< 11 500 K show a range of rotational velocities, with some stars showing vsin i up to 30km/s. •Apparently, the fast rotators are more abundant in NGC 1904, M13, and NGC 7078 than in NGC 2808 and NGC 6093 ( statistics? ). 2

  25. The spectroscopic approach ABUNDANCE ANALYSIS 10 stars in NGC 1904 Program: WIDTH3 (R. Gratton, addapted by D. Fabbian) Tested in 2 hot HB stars from the literature Stellar model atmosphere (Kurucz, 1998) Line list: Moore et al. 1966, Hambly et al. 1997, Kurucz & Bell (1995) Observed equivalent widths (EW) : ROSA (R. Gratton) 2

  26. The spectroscopic approach ABUNDANCE ANALYSIS • Atmospheric parameters (Teff, log g, ) Photometric Teff determination 2

  27. The spectroscopic approach ABUNDANCE ANALYSIS • Atmospheric parameters (Teff, log g, ) Photometric Teff determination Behr et al. (1999) measurements in M13 : log g = 4.83  log (Teff) – 15.74 = -4.7  log (Teff) + 20.9 2 • Error determinations ( EW, Teff, log g, , Z )

  28. The spectroscopic approach ABUNDANCE ANALYSIS [ Fe/H ] 2 log Teff (K)

  29. The spectroscopic approach ABUNDANCE ANALYSIS [ Ti/H ] 2 log Teff (K)

  30. The spectroscopic approach ABUNDANCE ANALYSIS [ Cr/H ] 2 log Teff (K)

  31. The spectroscopic approach ABUNDANCE ANALYSIS [ Y/H ] 2 log Teff (K)

  32. The spectroscopic approach ABUNDANCE ANALYSIS [ Mn/H ] 2 log Teff (K)

  33. The spectroscopic approach ABUNDANCE ANALYSIS [ P/H ] 2 log Teff (K)

  34. The spectroscopic approach ABUNDANCE ANALYSIS [ Ca/H ] 2 log Teff (K)

  35. The spectroscopic approach ABUNDANCE ANALYSIS [ He/H ] 2 log Teff (K)

  36. The spectroscopic approach ABUNDANCE ANALYSIS RESULTS • Radiative levitation of metals and helium depletion is detected for HB stars hotter than ~11 000 K in NGC 1904 for the first time. Fe, Ti, Cr and other metal species are enhanced to supersolar values. He abundance below the solar value. • Slightly higher abundances in NGC 1904 than in M13 (?) (Fabbian et al. 2003, in preparation). 2

  37. The spectroscopic approach POSSIBLE INTERPRETATIONS • Why some blue HB stars are spinning so fast? 1) Angular momentum transferred from the core to the outer envelope: Magnetic braking on MS only affects a star’s envelope(Peterson et al. 1983, Pinsonneault et al. 1991) Problems : Sun (Corbard et al. 1997, Charbonneau et al. 1999) Young stars (Queloz et al. 1998). Core rotation developed during the RGB(Sills & Pinsonneault 2000) Problems : no correlation between v sin i and the star’s distance to the ZAHB. 2) HB stars re-acquire angular momentum: Swallowing substellar objects(Peterson et al. 1983, Soker & Harpaz 2000.) Problems : No planets found in globular clusters yet. Close tidal encounters(Recio-Blanco et al. 2002). Problems : Only a small subset of impact parameters. 2

  38. The spectroscopic approach POSSIBLE INTERPRETATIONS • Why is there a discontinuity in the rotational velocity rate? Important : the change in velocity distribution can possibly be associate to the jump. • Angular momentum transfer prevented by a gradient in molecular weight (Sills & Pinsonneault 2000). 2) Removal of angular momentum due to the enhanced mass loss expected for Teff > 11 500 K(Recio-Blanco et al. 2002, Vink & Cassisi 2002 models). 2

  39. HOT HB STARS: BINARITY Intermediate resolution spectroscopy with FORS2 +VLT R  8000 (4 nights allocated). ~80 stars in 3 Galactic Globular clusters (NGC6752, NGC5986 and M80). Analysis procedure: Radial velocity variations with cross-correlation technique. 2

  40. HOT HB STARS: BINARITY 2 CMD by Momany et al. (2002) • First results comming soon => Graduate thesis by C. Moni Bidin

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