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 Photometry Database HB morpholgy analysis Results Conclusions

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

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

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

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

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

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

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

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

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

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

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

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

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

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 Sweigart (2001) 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).

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 Sweigart (2001) He Ti P Fe Si Cr Mg Ca CNO Behr et al. (2000)

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)

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)

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 Fast rotation Peterson et al. ( ) : M3, M4, M5, M13, NGC 288, halo. Cohen & McCarthy (1997) : M92 Behr et al. ( ) : M3, M13, M15, M68, M92, NGC 288. Kinman et al. (2000) : metal-poor halo

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 Fast rotation Many open questions on HB morphology and hot HB stars nature The origine of blue tails: why hot HB stars loose so much mass? Is there any relation between fast rotation and HB morphology? How is the distribution of stellar rotation along the HB? Which is the origine of fast stellar rotation on HB stars?

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

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

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

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

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

The spectroscopic approach ROTATIONAL VELOCITY Analysis procedure: Cross-correlation technique Projected rotational velocity (v sin i ) determined via the CCF (Tonry & Davis, 1979) using rotation standard stars of similar spectral type (Peterson et al. 1987). v sin i = A   -  = A   2 rot 22 o 

The spectroscopic approach ROTATIONAL VELOCITY Analysis procedure: Cross-correlation technique Projected rotational velocity (v sin i ) determined via the CCF (Tonry & Davis, 1979) using rotation standard stars of similar spectral type (Peterson et al. 1987). v sin i = A   -  = A   2 rot 22 o

The spectroscopic approach ROTATIONAL VELOCITY 2

The spectroscopic approach ROTATIONAL VELOCITY 2

The spectroscopic approach ROTATIONAL VELOCITY 2

The spectroscopic approach ROTATIONAL VELOCITY RESULTS Recio-Blanco et al., ApJL 572, 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 T eff > K have vsin i < 12 km/s - Stars with T eff < 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? ).

The spectroscopic approach ABUNDANCE ANALYSIS 2 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,...) Populations (abundances + excitation and ionizzation degrees calculated via the statistical equilibrium equations)

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

The spectroscopic approach ABUNDANCE ANALYSIS 2 Line list ( Moore et al. 1966, Hambly et al. 1997, Kurucz & Bell 1995) Observed equivalent widths ( EW ) Atmospheric parameters (T eff, log g,  ) Photometric Teff determination Behr et al. (1999) measurements in M13 : log g = 4.83  log (T eff ) –  = -4.7  log (T eff )

The spectroscopic approach ABUNDANCE ANALYSIS 2 Line list ( Moore et al. 1966, Hambly et al. 1997, Kurucz & Bell 1995) Observed equivalent widths ( EW ) Atmospheric parameters (T eff, log g,  ) Photometric Teff determination Behr et al. (1999) measurements in M13 : log g = 4.83  log (T eff ) –  = -4.7  log (T eff ) Error determinations ( EW, T eff, log g, , Z )

The spectroscopic approach ABUNDANCE ANALYSIS 2 [ Fe/H ] log T eff (K)

The spectroscopic approach ABUNDANCE ANALYSIS 2 log T eff (K) [ Ti/H ]

The spectroscopic approach ABUNDANCE ANALYSIS 2 log T eff (K) [ Cr/H ]

The spectroscopic approach ABUNDANCE ANALYSIS 2 log T eff (K) [ Y/H ]

The spectroscopic approach ABUNDANCE ANALYSIS 2 log T eff (K) [ Mn/H ]

The spectroscopic approach ABUNDANCE ANALYSIS 2 log T eff (K) [ P/H ]

The spectroscopic approach ABUNDANCE ANALYSIS 2 log T eff (K) [ Ca/H ]

The spectroscopic approach ABUNDANCE ANALYSIS 2 log T eff (K) [ Mg/H ]

The spectroscopic approach ABUNDANCE ANALYSIS 2 log T eff (K) [ He/H ]

The spectroscopic approach ABUNDANCE ANALYSIS RESULTS Fabbian, Recio-Blanco et al. 2003, in preparation 2 Radiative levitation of metals and helium depletion is detected for HB stars hotter than ~ 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).

The spectroscopic approach POSSIBLE INTERPRETATIONS 2 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.

The spectroscopic approach 2 Why is there a discontinuity in the rotational velocity rate? Important : the change in velocity distribution can possibly be associate to the jump. 1)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 > K (Recio-Blanco et al. 2002, Vink & Cassisi 2002 models). POSSIBLE INTERPRETATIONS

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

The photometric approach 2 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.

The photometric approach 2 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.

The photometric approach 2 What determines GC HB morphology? Determination of the highest effective temperature reached by the stars in the HB: fitting ZAHB models (Cassisi et al. 1999) to the observed CMDs

The photometric approach 2 What determines GC HB morphology? Determination of the highest effective temperature reached by the stars in the HB: fitting ZAHB models (Cassisi et al. 1999) to the observed CMDs ZAHB 9000 K K K T eff HB

The photometric approach 2 What determines GC HB morphology? Determination of the highest effective temperature reached by the stars in the HB: fitting ZAHB models (Cassisi et al. 1999) to the observed CMDs Determination of distance moduli and reddening in flight system for each cluster. ZAHB 9000 K K K T eff HB

The photometric approach 2 What determines GC HB morphology? Determination of the highest effective temperature reached by the stars in the HB: fitting ZAHB models (Cassisi et al. 1999) to the observed CMDs Determination of distance moduli and reddening in flight system for each cluster. Calculation of the ZAHB apparent and absolute magnitude from the RR-Lyrae level (5 templates taken from the literature).

The photometric approach 2 What determines GC HB morphology? Determination of the highest effective temperature reached by the stars in the HB: fitting ZAHB models (Cassisi et al. 1999) to the observed CMDs Determination of distance moduli and reddening in flight system for each cluster. Calculation of the ZAHB apparent and absolute magnitude from the RR-Lyrae level (5 templates taken from the literature). m = m [M/H] M = [ M/H] [ M/H] 2 ZAHB F555W RR-Lyrae

The photometric approach 2 What determines GC HB morphology? Determination of the highest effective temperature reached by the stars in the HB: fitting ZAHB models (Cassisi et al. 1999) to the observed CMDs Determination of distance moduli and reddening in flight system for each cluster. Calculation of the ZAHB apparent and absolute magnitude from the RR-Lyrae level (5 templates taken from the literature). m = m  M = [ M/H] [ M/H] 2 ZAHB F555W le F555W

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. log(T eff ) HB, [Fe/H], M V,  col    c, R GC, L, B, r c, r h, t rc, t rh,  v

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Monovariate correlations

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Monovariate correlations log(T eff ) HB [Fe/H]

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Monovariate correlations log(T eff ) HB MvMv

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Monovariate correlations log(T eff ) HB  col

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Monovariate correlations log(T eff ) HB oo

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Monovariate correlations log(T eff ) HB R GC

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Subset of clusters in common with Rosenberg et al. (2000) Monovariate correlations log(T eff ) HB Relative Age

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Principal Component Analysis Diagonalization of the correlation matrix => new system of the eigenvectors

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Principal Component Analysis Diagonalization of the correlation matrix => new system of the eigenvectors The number of significative eigenvalues gives the dimensionality of the dataset. e i = Eigenvector´s value V i = Associated variance C i = Cumulative variance

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Bivariate correlations log(T eff ) HB [Fe/H] – 0.60 Mv

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Bivariate correlations [Fe/H] log(T eff ) HB

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Bivariate correlations log(T eff ) HB [Fe/H] – 0.57  col

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Bivariate correlations log(T eff ) HB [Fe/H] – 0.96  col

The photometric approach 2 What determines GC HB morphology? Multivariate approach of the HB highest temperature dependence on cluster parameters. Trivariate correlations log(T eff ) HB [Fe/H] – 0.37 Mv  col

The photometric approach 2 Total mass and stellar collisions seem to influence the observed horizontal branch morphologies of Galactic globular clusters. More massive clusters (or those with higher probablilty of stellar collisions) tend to have more extended HBs. RESULTS Recio-Blanco et al., 2003, in preparation No important dependence has been found on cluster density or other cluster parameters.

The photometric approach 2 Close encounters and tidal stripping in the bigger and more concentrated clusters (those with a higher probability of stellar collisions) POSSIBLE INTERPRETATIONS Helium enhancement due to a more effective self-polution in the more massive clusters.

CONCLUSIONS 2 The presence of fast HB rotators is confirmed and extended to other clusters. The abundance of fast HB rotators can apparently change from cluster to cluster. The change in rotational velocity seems to be associated to the onset of diffusive processes in the stellar atmosphere. Radiative levitation of metals and gravitational settling of helium has been observed at the level of the luminosity jump in NGC 1904 Total mass and stellar collisions seem to influence the observed horizontal branch morphologies with effects larger than those of age. No important dependence of the HB morphology has been found on cluster density or other cluster parameters.