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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
Asymptotic Giant
Branch
Horizontal Branch
Red Giant
Branch
Main
Sequence
Globular clusters are gravitationally bound, coeval, and
chemically homogeneous concentrations of stars.
Theoretical and observational framework
Asymptotic Giant
Branch
Horizontal Branch Red Giant
Branch
Main
Sequence
Globular clusters are gravitationally bound, coeval, and
chemically homogeneous concentrations of stars.
Theoretical and observational framework
Same core mass
(0.5 M)
Different total
mass.
Asymptotic Giant
Branch
Horizontal Branch Red Giant
Branch
Main
Sequence
HB
morphology
Core-helium burning and shell-hydrogen burning
Theoretical and observational framework
Same core mass
(0.5 M)
Different total
mass.
Asymptotic Giant
Branch
Horizontal Branch Red Giant
Branch
Main
Sequence
HB
morphology
Pop II stellar
evolution.
Distance
indicator (RR
Lyrae)
Lower limit to
the age of the
Universe
Core-helium burning and shell-hydrogen burning
Theoretical and observational framework
Same core mass
(0.5 M)
Different total
mass.
Blue tail
Asymptotic Giant
Branch
Red Giant
Branch
Main
Sequence
HB
morphology
•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.
HB
morphology
Metallicity:
the first parameter
Theoretical and observational framework
Same core mass
(0.5 M)
Different total
mass.
HB
morphology
Rosenberg et al. (2000)
Second
parameter(s)
Theoretical and observational framework
Same core mass
(0.5 M)
Other parameters
Different total
mass.
•Age
• He mixing
HB
morfology
•[CNO/Fe]
Second parameter(s)
Theoretical and observational framework
Blue Tails
More possible
second parameters
The most extreme
espresion of the
second parameter
problem
• Concentration
• Rotation
• Planets
• Self enrichment
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
Ferraro et al. (1998)
Differences in:
• Gaps: regions
underpopulated in
stars, which appear
in the blue HB
sequences of many
globular clusters.
Evolution
Mass loss
[CNO/Fe]
He mixing
Rotation
Origin (binaries)
Abundances
Same mass or same temperature
Theoretical and observational framework
Blue Tails
• Gaps: regions
underpopulated in
stars, which appear
in the blue HB
sequences of many
globular clusters.
Sweigart (2001)
• Diffusive processes:
Abundance anomalies
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:
Sweigart (2001)
He
Fe
Mg
Ti
Si
Ca
P
Cr
CNO
Abundance anomalies
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 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 ~ 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 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  2 - 2o = A   rot
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  2 - 2o = A   rot
2
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, 2002
• 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.
2
• 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
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)
2
Transition probabilities (oscilator strengths, damping
coefficient,...)
Populations (abundances + excitation and ionizzation
degrees calculated via the statistical equilibrium equations)
The spectroscopic approach
ABUNDANCE ANALYSIS
• 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
2
The spectroscopic approach
ABUNDANCE ANALYSIS
• 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

 = -4.7 
2
log (Teff) – 15.74
log (Teff) + 20.9
The spectroscopic approach
ABUNDANCE ANALYSIS
• 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

 = -4.7 
2
log (Teff) – 15.74
log (Teff) + 20.9
• Error determinations ( EW, Teff, log g, , Z )
The spectroscopic approach
ABUNDANCE ANALYSIS
2
log Teff (K)
The spectroscopic approach
ABUNDANCE ANALYSIS
2
log Teff (K)
The spectroscopic approach
ABUNDANCE ANALYSIS
2
log Teff (K)
The spectroscopic approach
ABUNDANCE ANALYSIS
2
log Teff (K)
The spectroscopic approach
ABUNDANCE ANALYSIS
2
log Teff (K)
The spectroscopic approach
ABUNDANCE ANALYSIS
2
log Teff (K)
The spectroscopic approach
ABUNDANCE ANALYSIS
2
log Teff (K)
The spectroscopic approach
ABUNDANCE ANALYSIS
2
log Teff (K)
The spectroscopic approach
ABUNDANCE ANALYSIS
2
log Teff (K)
The spectroscopic approach
ABUNDANCE ANALYSIS RESULTS
Fabbian, Recio-Blanco et al. 2003, in preparation
• 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).
2
The spectroscopic approach
POSSIBLE INTERPRETATIONS
• 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:
2
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
POSSIBLE INTERPRETATIONS
• 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).
2
The photometric approach
Database: HST snapshot (Piotto et al. 2002)
74 Globular clusters
HST/WFPC2 observed in
F439W and F555W
PC on the cluster center
2
The photometric approach
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
2
Transformation to standard
photometric systems.
The photometric approach
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
2
Transformation to standard
photometric systems.
The photometric approach
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
The photometric approach
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
9000 K
14000 K
18000 K
2
Teff
HB
ZAHB
•
The photometric approach
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.
9000 K
14000 K
18000 K
2
Teff
HB
ZAHB
•
The photometric approach
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).
2
The photometric approach
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 F555W
= mF555W+ 0.152 + 0.041 [M/H]
ZAHB
RR-Lyrae
2
M F555W
=
ZAHB
0.9824 + 0.3008 [ M/H] +
0.0286 [ M/H] 2
The photometric approach
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 F555W
= mF555W+ 0.152 - 3F555W+ 0.1
ZAHB
le
2
M F555W
=
ZAHB
0.9824 + 0.3008 [ M/H] +
0.0286 [ M/H] 2
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
log(Teff)HB, [Fe/H], MV,col, o , c, RGC, L, B, rc, rh, trc, trh, v
2
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
Monovariate correlations
2
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
Monovariate correlations
2
[Fe/H]
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
Monovariate correlations
2
Mv
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
Monovariate correlations
2
col
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
Monovariate correlations
2
o
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
Monovariate correlations
2
RGC
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
Monovariate correlations
Subset of clusters
in common with
Rosenberg et al.
(2000)
2
Relative Age
The photometric approach
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
2
The photometric approach
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
2
dimensionality of the
dataset.
ei = Eigenvector´s value Vi = Associated variance Ci = Cumulative variance
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
Bivariate correlations
2
-0.79 [Fe/H] – 0.60 Mv
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
Bivariate correlations
2
[Fe/H]
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
Bivariate correlations
2
-0.83 [Fe/H] – 0.57 col
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
Bivariate correlations
2
-0.22 [Fe/H] – 0.96 col
The photometric approach
What determines GC HB morphology?
Multivariate approach of the HB highest temperature dependence on
cluster parameters.
Trivariate correlations
2
-0.57 [Fe/H] – 0.37 Mv + 0.96 col
The photometric approach
RESULTS
Recio-Blanco et al., 2003, in preparation
• 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.
• No important dependence has been found on cluster density or other
cluster parameters.
2
The photometric approach
POSSIBLE INTERPRETATIONS
• 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.
2
CONCLUSIONS
• 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
2
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.