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

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


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



Main Sequence

Red Giant Branch

Horizontal Branch

Asymptotic Giant Branch


Main Sequence

Red Giant Branch

Horizontal Branch




Core-helium burning and shell-hydrogen burning

Main Sequence

Red Giant Branch


Same core mass (0.5 M)

Different total mass.

HB morphology

Horizontal Branch


Core-helium burning and shell-hydrogen burning

Main Sequence

Red Giant Branch




HB morphology

Horizontal Branch

Pop II stellar evolution.

Distance indicator (RR Lyrae)

Lower limit to the age of the Universe


Main Sequence

Red Giant Branch




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.




Metallicity:

the first parameter

HB morphology




Rosenberg et al. (2000)

Second parameter(s)

HB morphology




HB morfology

Second parameter(s)

Other parameters

•Age

• He mixing

•[CNO/Fe]


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


Blue Tails

• Gaps: regions underpopulated in stars, which appear in the blue HB sequences of many globular clusters.


Blue Tails


Piotto et al. (1999)

Same mass


Blue Tails


Ferraro et al. (1998)

Same mass or same temperature

Differences in:

Evolution

Mass loss

[CNO/Fe]

He mixing

Rotation

Origin (binaries)

Abundances


Blue Tails


• 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).


Blue Tails



Sweigart (2001)

He

Ti

P

Fe

Si

Cr

Mg

Ca

CNO

Behr et al. (2000)


Blue Tails



Low gravities•Moehler et al. (1995, 1997, 2000)•de Boer et al. (1995)•Crocker et al. (1998)


Blue Tails



Low gravities

Luminosity jump

Grundahl et al. (1999)


Blue Tails



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


Blue Tails



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



Exposure times: 800s – 2.5 h/star

61 hot HB stars observed



Exposure times: 800s – 2.5 h/star

61 hot HB stars observed


DATA REDUCTION

IRAF package:

Bias subtraction, flat fielding

Order tracing and extraction

Calibration


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


ROTATIONAL VELOCITY


v sin i = A - = A

2

rot2 2

o


ROTATIONAL VELOCITY


v sin i = A - = A

2

rot2 2

o


ROTATIONAL VELOCITY

2


ROTATIONAL VELOCITY

2


ROTATIONAL VELOCITY

2


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? ).


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)


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


ABUNDANCE ANALYSIS

2




Behr et al. (1999) measurements in M13 :

log g = 4.83 log (Teff) – 15.74

= -4.7 log (Teff) + 20.9


ABUNDANCE ANALYSIS

2




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 )


ABUNDANCE ANALYSIS

2

[ F

e/H

]

log Teff (K)


ABUNDANCE ANALYSIS

2

log Teff (K)

[ T

i/H

]


ABUNDANCE ANALYSIS

2

log Teff (K)

[ C

r/H

]


ABUNDANCE ANALYSIS

2

log Teff (K)

[ Y

/H ]


ABUNDANCE ANALYSIS

2

log Teff (K)

[ M

n/H

]


ABUNDANCE ANALYSIS

2

log Teff (K)

[ P

/H ]


ABUNDANCE ANALYSIS

2

log Teff (K)

[ C

a/H

]


ABUNDANCE ANALYSIS

2

log Teff (K)

[ M

g/H

]


ABUNDANCE ANALYSIS

2

log Teff (K)

[ H

e/H

]


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).


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.


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).


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


2





Reduction procedures:

DAOPHOT II/ALLFRAME (P.B. Stetson)

Correction for CTE

Transformation to standard photometric systems.


2





Reduction procedures:

DAOPHOT II/ALLFRAME (P.B. Stetson)

Correction for CTE

Transformation to standard photometric systems.


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

•


2


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


2


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


2



Calculation of the ZAHB apparent and absolute magnitude from the RR-Lyrae level (5 templates taken from the literature).


2



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


2



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


2


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


2



Monovariate correlations


2



Monovariate correlationslo

g(T

eff)

HB

[Fe/H]


2




g(T

eff)

HB

Mv


2




g(T

eff)

HB

col


2




g(T

eff)

HB

o


2




g(T

eff)

HB

RGC


2



Subset of clusters in common with Rosenberg et al. (2000)


g(T

eff)

HB

Relative Age


2



Principal Component Analysis

Diagonalization of the correlation matrix => new system of the eigenvectors


2



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


2



Bivariate correlations

log(

Tef

f)H

B

-0.79 [Fe/H] – 0.60 Mv


2




[Fe/H]

log(

Tef

f)H

B


2




log(

Tef

f)H

B

-0.83 [Fe/H] – 0.57 col


2




log(

Tef

f)H

B

-0.22 [Fe/H] – 0.96 col


2



Trivariate correlations

log(

Tef

f)H

B

-0.57 [Fe/H] – 0.37 Mv + 0.96 col


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.


2

• Close encounters and tidal stripping in the bigger and more concentrated clusters (those with a higher probability of stellar collisions)


•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.

Documents

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