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

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

ResultsConclusions

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?Menv < 0.2 M Temperatures

up to ~ 35 000 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. (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

DATA REDUCTION

IRAF package:

Bias subtraction, flat fielding

Order tracing and extraction

Calibration

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

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 (Teff, 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 (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

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 (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)

[ M

g/H

]

The spectroscopic approach

ABUNDANCE ANALYSIS

2

log Teff (K)

[ H

e/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 ~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).

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

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

•

ZAHB9000 K

14000 K

18000 K

TeffHB

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 CMDsDetermination of distance moduli and reddening in flight system for each cluster.

•

ZAHB9000 K

14000 K

18000 K

TeffHB

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 CMDsDetermination 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 CMDsDetermination 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 + 0.152 + 0.041 [M/H] M = 0.9824 + 0.3008 [ M/H] + 0.0286 [ M/H] 2

ZAHB

ZAHB

F555W

F555W

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 CMDsDetermination 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 + 0.152 - 3 + 0.1 M = 0.9824 + 0.3008 [ M/H] + 0.0286 [ M/H] 2

ZAHB

ZAHB

F555W

F555W

F555W

le

F555W

The photometric approach

2

What determines GC HB morphology?

Multivariate approach of the HB highest temperature dependence on cluster parameters.

log(Teff)HB, [Fe/H], MV,colc, RGC, L, B, rc, rh, trc, trh, 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 correlationslo

g(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 correlationslo

g(T

eff)

HB

Mv

The photometric approach

2

What determines GC HB morphology?

Multivariate approach of the HB highest temperature dependence on cluster parameters.

Monovariate correlationslo

g(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 correlationslo

g(T

eff)

HB

o

The photometric approach

2

What determines GC HB morphology?

Multivariate approach of the HB highest temperature dependence on cluster parameters.

Monovariate correlationslo

g(T

eff)

HB

RGC

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 correlationslo

g(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.

ei = Eigenvector´s value Vi = Associated variance Ci = 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(

Tef

f)H

B

-0.79 [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(

Tef

f)H

B

The photometric approach

2

What determines GC HB morphology?

Multivariate approach of the HB highest temperature dependence on cluster parameters.

Bivariate correlations

log(

Tef

f)H

B

-0.83 [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(

Tef

f)H

B

-0.22 [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(

Tef

f)H

B

-0.57 [Fe/H] – 0.37 Mv + 0.96 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.

RESULTSRecio-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.