Exotic populations in

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Bologna, January 29, 2008
Exotic populations in
Galactic Globular Clusters
Francesco R. Ferraro
Dip. di Astronomia - Univ. di Bologna (ITALY)
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ASTRO ARCHEOLOGY TRACERS of the
structure history of the Galaxy
ASTRO TIMING LABORATORY for
theoretical models of stellar evolution
GALACTIC GLOBULARCLUSTERS
ASTRO DYNAMICS LABORATORY
environment ? SE
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EXOTIC OBJECTS
probing the cluster dynamics

• the photometric properties, the incidence and
  the spatial distribution of collisionally induced
  
• stellar populations show signatures of the
  cluster
• dynamical evolution

• better understanding of the relaxation and the
• core collapse process and the role of the
  binary
• systems in the dynamical evolution of the
  parent
• cluster

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Exotic populations in the CMD
UVE
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HST
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Exotics in the UV
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Blue Straggler Stars
BSS have been detected for the first time by
Sandage (1953)
according to their position in the CMD,
BSS should be more massive than normal
stars (see also Shara et al 1997)
direct Collisions ..in the central region
of high density GCs
primordial Binaries evolving in isolation In
low density GCs
?
COL-BSS
PB-BSS
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Blue Straggler Stars
lt1990
gt1990
Paresce et al (1991,Nature,352,297)
BSS are a common population of GGCs,
found in each cluster properly observed

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BSS in the UV
UV-plane ideal to study the
photometric properties of the BSS
population - the distribution is almost
vertical - span more than 3 magnitudes
Ferraro et al (1997,AA,324,915)
Ferraro et al (2001,ApJ,561,337)
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M80 is the densest, not-PCC cluster of the
Galaxy Log r0 5.8 Ms/pc3
BSS in the UV
The large population in M80
305 BSS !! The largest population
ever observed in a GGC
The most concentrated BSS population ever
found in a GGC
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The large population of BSS in M80
Why M80 has such a large population of BSS ?
M80 is a quite concentrated cluster (Log r0
5.8 Ms/pc3) BUT other clusters with similar
concentration like 47 Tuc (Log r0 5.1
Ms/pc3) NGC2808 (Log r0 5.0 Ms/pc3) NGC6388
(Log r0 5.7 Ms/pc3) have many fewer BSS
(NBSSlt 100)
Could the dynamical evolution of the cluster
play a role in the formation of BSS?
M80 is not a PCC but
it should be !!!! its dynamical time
scale is much shorter than its age !

Are collisions delaying the core collapse
and generating COL-BSS?
This would be the first direct evidence !!!
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Blue sequences in the UV
direct comparison of BSS populations
PCC? NBSS 17 F 0.16
collapsing NBSS 129 F 0.44 1.0
?
binaries are preventing core collapse ?
are binaries destroyed during the collapse ?
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Blue sequences in the UV
direct comparison of BSS populations
twin clusters
M 3 Log r0 3.5 Ms/pc3 Log M 5.8 Ms NBSS
72 F 0.28
M 13 Log r0 3.4 Ms/pc3 Log M 5.8
Ms NBSS 16 F 0.07
?
different primordial binary population ?
clusters in different dynamical phases ?
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Which is the binary fraction in GGCs ?
The Binary fraction in 13 low-density clusters
from ACS-HST observations
12-13 16-22 16-21 28-40
12-15 14-19 11-12
10-12 13-17 16-21
33-50 51-65 41-51
Sollima et al (2007, MNRAS, 380,781)
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M3
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BSS radial distributions
Radius of avoidance
Radius at which all objects with a mass similar
to BSS have been sunk into the core in a time
comparable to the cluster age
Important signatures of the dynamical evolution
of the parent cluster is imprinted in the BSS
properties
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IBs and UV-excess stars in GGCs
IBs LMXB accreting NS in binary systems
LLXGC acceting WD in binary systems
These objects are 100 times more abundant in GCs
with respect to the field !!!! (collisional
origin)
X-ray CHANDRA catalog by Grindlay et al 2001
V1 Paresce, De Marchi Ferraro (1992)
V2 Dwarf Nova Paresce De Marchi (1994)
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UV-excess stars in GGCs
47 Tuc
ONLY the brightest portion of the IB region has
been explored!!!
M15
Knigge et al (2002, ApJ,579,752)
An extensive search for IBs in GCs is still
lacking - Which process generate IBs? COL
PB ? - Are IBs less abundant in the core of
high density GCs? - Are collisions destroying or
creating IBs?
Dieball et al (2007,ApJ,670,379)
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What do we need?

• High resolution
• 2. UV sensitivity

WFC2
WFC3/UVIS
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Exotic stellar populations the MSP companions
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Optical companions to MSP in GGCs
THE MSP RE-CYCLING SCENARIO - MSP are thought to
form in binary systems containing a NS which is
eventually spun up through mass accretion from an
evolving companion The result will be a new born
MSP an exhausted star (which has lost most of
its envelope) the core of a peeled star
(He-WD). 50 of the Galaxy MSP have been found
in GGCs Optical identification of MSP companion
optical and spectroscopic follow-up. Light
curve orbital inclination mass ratio from the
velocity curve empirical estimate of the pulsar
mass .. Constraining the state of the degenerate
matter in a neutron star
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Optical companion to MSP in GGCs
47 TUC
Fully consistent with the canonical scenario of
the MSP recycling process
He WD
Edmonds et al (2001)
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The bright companion to the MSP in NGC6397
MSP J1740-5340 in NGC6397 shows eclipse of
the radio signal for about 40 of the orbit
(DAmico et al 2001) suggesting that the NS is
orbiting within a large envelope of matter
released by the companion
COMJ1740 is NOT a WD as expected
in the framework of the
MSP recycling scenario
Star A is the MSP companion ( COMJ1740)
Ferraro et al (2001,ApJ,561,L93)
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The bright companion to the MSP in NGC6397
COM J1740 is tidally distorted and
is loosing mass from its
Roche lobe
Burderi et al (2002) suggested that the position
of COMJ1740 in the CMD is consistent with the
evolution of a slighly evolved TO star orbiting
the NS and loosing mass. The evolution would
generate a He-WD
This bright object is the ideal target for
Spectroscopic follow-up.
High-resolution spectroscopic campaign with
UVES_at_VLT
Mass0.3 Mo !!!!!
Ferraro et al (2002,ApJ, 584,L13) Sabbi et al
(2003, ApJ,589,L41)
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COMJ1740 has the same overall chemical
composition of the SGBs
No C in the COM J1740-5340 atmosphere. This
would suggests a CN cycle at equilibrium, (when
all C has been burned to N), hence it is a
deeply peeled star (Ergma Sarna 2003)
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The bright companion to the MSP in NGC6397
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Optical companion to MSP in GGCs
U in 47 Tuc 0.2 Mo He-WD Edmonds et al (2001)
COMJ1740-5340 in NGC6397 0.3 Mo (pre
He-WD) Ferraro et al (2001)
CO-WD
He-WD
COMJ1701-3600B in NGC6266 ?? Mo (pre
He-WD) Cocozza et al (2007)
W in 47 Tuc 0.13 Mo MS Edmonds et al (2002)
COMB1620-26 in M4 0.3 Mo He-WD Sigurdsson et al
(2003)
COMJ1911-5958 in NGC6752 0.2 Mo He-WD Ferraro
et al (2003),Bassa et al (2003)
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MSPs in NGC6266 (M62)
6 MSPs have been discovered in this cluster by
DAmico et al (2001a,b) and Jacoby et al
(2002) 51 X-ray sources (Pooley et al 2002)
All the MSPs discovered so far in NGC6266 are in
binary systems
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MSPs in Terzan 5
PC WFPC2
NICMOS
33 MSPs have been discovered in TERZAN 5 this
is the largest population of MSP ever detected in
a GC
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What do we need?

• High resolution
• 2. High sensitivity in the IR

NICMOS/NIC3
WFC3/IR
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LOOKING FOR IMBH SIGNATURES in GCs
The confirmation of the existence and the
frequency of IMBH in GCs is one of the most
exciting challenge for the new HST era In the
litterature there are a few debated examples M15
(van der Marel et al 2002, Baumgardt et al
(2003) G1 in M31 (Gebhardt et al 2002).
A number of potential targets have been
suggested by Noyola and Gebhardt (2006) on the
basis of small deviation of the surface
brightness profile from the canonical King
Model
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IMBHs which signatures? (Baumgardt et al. 2005
Miocchi 2007 Heggie et al. 2007 Trenti et al.
2007 Dukier Bailyn 2003 Maccarone 2004)

• 1) intermediate concentration (c1.8) King
  profile,
• with power-law deviation at the very center
  
• ?(r) r -0.2 at r lt 0.1 rc
• PCC clusters c gt 2, ?(r) r -0.8

2) sharp rise in the central velocity dispersion
profile (at r lt 0.05 rc)
3) presence of few high-velocity (even v 100
km/s) stars
possible X-ray and radio emission from
accreting gas
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SEARCHING FOR IMBH SIGNATURES in GCs
By using a combination of ACS.HR/WFC,WFPC2 and
wide field observations Lanzoni et al (2007, ApJ,
668, L139) has found such a signature in the star
density profile of NGC6388.
c 1.8 rc 7.2 MBH 6 103 Mo
Attention!!! The critical point here is the
accurate determination of the center of gravity
of the cluster small (0.5 arcsec) errors in the
center determination can clear-out the SB effect
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NGC 6388
Determination of the centre
V lt 20 ( 4000 stars)
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• High resolution
• 2. Large field of view

What do we need?

• ULTRA-ACCURATE SB SD profiles for the promising
  clusters High resolution (ACS/HRC) WFC3/UVIS
• MULTI-EPOCH HR images of the center Accurate
  proper motion (a few MAS) measures to detect
  High velocity stars (vgt100 Km/s)

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The End