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?Menv < 0.2 M Temperatures

up to ~ 35 000 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. (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

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

natureThe 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 ~ 40 000 => 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 techniqueProjected 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 techniqueProjected 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

rot2 2

o

The spectroscopic approach

ROTATIONAL VELOCITY

Analysis procedure: Cross-correlation techniqueProjected 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

rot2 2

o

The spectroscopic approach

ROTATIONAL VELOCITY

2

The spectroscopic approach

ROTATIONAL VELOCITY

2

The spectroscopic approach

ROTATIONAL VELOCITY

2

The spectroscopic approach

ROTATIONAL VELOCITY RESULTSRecio-Blanco et al., ApJL 572, 2002

2

• 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? ).

The spectroscopic approach

ABUNDANCE ANALYSIS

2

10 stars in NGC 1904Program: 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 (Teff, log g, )

Photometric Teff determination

The spectroscopic approach

ABUNDANCE ANALYSIS

2

• 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

• Error determinations ( EW, Teff, log g, , Z )

The spectroscopic approach

ABUNDANCE ANALYSIS

2

[ F

e/H

]

log Teff (K)

The spectroscopic approach

ABUNDANCE ANALYSIS

2

log Teff (K)

[ T

i/H

]

The spectroscopic approach

ABUNDANCE ANALYSIS

2

log Teff (K)

[ C

r/H

]

The spectroscopic approach

ABUNDANCE ANALYSIS

2

log Teff (K)

[ Y

/H ]

The spectroscopic approach

ABUNDANCE ANALYSIS

2

log Teff (K)

[ M

n/H

]

The spectroscopic approach

ABUNDANCE ANALYSIS

2

log Teff (K)

[ P

/H ]

The spectroscopic approach

ABUNDANCE ANALYSIS

2

log Teff (K)

[ C

a/H

]

The spectroscopic approach

ABUNDANCE ANALYSIS

2

log Teff (K)

[ H

e/H

]

The spectroscopic approach

ABUNDANCE ANALYSIS RESULTS

2

• 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).

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 > 11 500 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

2CMD by Momany et al. (2002)

• First results comming soon => Graduate thesis by C. Moni Bidin