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NATURALEZA DE LAS ESTRELLAS CALIENTES DE RAMA HORIZONTAL EN CÚMULOS GLOBULARES GALÁCTICOS. Tesis presentada por A. Recio Blanco. Directores: A. Aparicio Juan G. Piotto. Theoretical and observational framework. Spectroscopic approach Observations Analysis Results.

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NATURALEZA DE LAS ESTRELLAS CALIENTES DE RAMA HORIZONTAL EN CÚMULOS GLOBULARES GALÁCTICOS


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    1. NATURALEZA DE LAS ESTRELLAS CALIENTES DE RAMA HORIZONTAL EN CÚMULOS GLOBULARES GALÁCTICOS Tesis presentada por A. Recio Blanco Directores: A. Aparicio Juan G. Piotto

    2. Theoretical and observational framework Spectroscopic approach Observations Analysis Results Photometry Database HB morpholgy analysis Results Conclusions

    3. Theoretical and observational framework Globular clusters are gravitationally bound, coeval, and chemically homogeneous concentrations of stars.

    4. Theoretical and observational framework Asymptotic Giant Branch Horizontal Branch Red Giant Branch Main Sequence Globular clusters are gravitationally bound, coeval, and chemically homogeneous concentrations of stars.

    5. Theoretical and observational framework Asymptotic Giant Branch Horizontal Branch Red Giant Branch Main Sequence Globular clusters are gravitationally bound, coeval, and chemically homogeneous concentrations of stars.

    6. Theoretical and observational framework Same core mass (0.5 M) Different total mass. Asymptotic Giant Branch Horizontal Branch Red Giant Branch Main Sequence HB morphology Core-helium burning and shell-hydrogen burning

    7. Theoretical and observational framework Same core mass (0.5 M) Different total mass. Pop II stellar evolution. Asymptotic Giant Branch Horizontal Branch Red Giant Branch Distance indicator (RR Lyrae) Main Sequence Lower limit to the age of the Universe HB morphology Core-helium burning and shell-hydrogen burning

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

    9. Theoretical and observational framework Same core mass (0.5 M) Different total mass. HB morphology Metallicity: the first parameter

    10. Theoretical and observational framework Same core mass (0.5 M) Different total mass. Rosenberg et al. (2000) HB morphology Second parameter(s)

    11. Theoretical and observational framework Same core mass (0.5 M) Different total mass. Other parameters •Age • He mixing •[CNO/Fe] HB morfology Second parameter(s)

    12. Theoretical and observational framework Blue Tails More possible second parameters The most extreme espresion of the second parameter problem • Concentration • Rotation • Planets • Self enrichment Why hot HB stars can loose so much mass? Menv< 0.2 M Temperatures up to ~ 35 000 K

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

    14. 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

    15. 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

    16. 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

    17. 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)

    18. 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)

    19. 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)

    20. 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

    21. 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

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

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

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

    25. The spectroscopic approach DATA REDUCTION IRAF package: Bias subtraction, flat fielding Order tracing and extraction Calibration

    26. 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

    27. 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

    28. 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

    29. The spectroscopic approach ROTATIONAL VELOCITY 2

    30. The spectroscopic approach ROTATIONAL VELOCITY 2

    31. The spectroscopic approach ROTATIONAL VELOCITY 2

    32. 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

    33. 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 Reproducing the observed equivalent widths, solving the equation of radiative transfer with: Stellar model atmosphere (Kurucz, 1998) Opacity (sources: HI, H, HeI, CI, AlI, MgI, SiI, Rayleigh and Thomson diffusion, atomic lines) Transition probabilities (oscilator strengths, damping coefficient,...) 2 Populations (abundances + excitation and ionizzation degrees calculated via the statistical equilibrium equations)

    34. The spectroscopic approach ABUNDANCE ANALYSIS • Line list (Moore et al. 1966,Hambly et al. 1997, Kurucz & Bell 1995) • Observed equivalent widths (EW) • Atmospheric parameters (Teff, log g, ) Photometric Teff determination 2

    35. The spectroscopic approach ABUNDANCE ANALYSIS • Line list (Moore et al. 1966,Hambly et al. 1997, Kurucz & Bell 1995) • Observed equivalent widths (EW) • 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

    36. The spectroscopic approach ABUNDANCE ANALYSIS • Line list (Moore et al. 1966,Hambly et al. 1997, Kurucz & Bell 1995) • Observed equivalent widths (EW) • 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 )

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

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

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

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

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

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

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

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

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

    46. The spectroscopic approach ABUNDANCE ANALYSIS RESULTS Fabbian, Recio-Blanco et al. 2003, in preparation • 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, Recio-Blanco et al. 2003, in preparation). 2

    47. 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

    48. 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

    49. The photometric approach Database: HST snapshot (Piotto et al. 2002) 74 Globular clusters HST/WFPC2 observed in F439W and F555W PC on the cluster center 2

    50. The photometric approach Database: HST snapshot (Piotto et al. 2002) 74 Globular clusters HST/WFPC2 observed in F439W and F555W PC on the cluster center Reduction procedures: DAOPHOT II/ALLFRAME (P.B. Stetson) Correction for CTE Transformation to standard photometric systems. 2