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. HB morphology Horizontal Branch

Theoretical and observational framework 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 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

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

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 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)

The spectroscopic approach ABUNDANCE ANALYSIS 2 Atmospheric parameters (T eff, log g,  ) Photometric Teff determination

The spectroscopic approach ABUNDANCE ANALYSIS 2 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) [ He/H ]

The spectroscopic approach ABUNDANCE ANALYSIS RESULTS 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 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

HOT HB STARS: BINARITY 2 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.

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