Bologna, January 29, 2008

ASTRO – ARCHEOLOGY TRACERS TRACERS of the structure & history of the Galaxy of the Galaxy ASTRO – ARCHEOLOGY TRACERS TRACERS of the structure & history of the Galaxy of the Galaxy ASTRO – TIMING LABORATORY LABORATORY for theoretical models of stellar evolution of stellar evolution ASTRO – TIMING LABORATORY LABORATORY for theoretical models of stellar evolution of stellar evolution ASTRO – DYNAMICS LABORATORY LABORATORY environment  SE environment  SE ASTRO – DYNAMICS LABORATORY LABORATORY environment  SE environment  SE

EXOTIC OBJECTS: 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 the photometric properties, the incidence and the spatial distribution of collisionally induced stellar populations show signatures of the cluster dynamical evolution probing the cluster dynamics

UVE by-products of binary systems “perturbing” “perturbing” effects on “canonical” effects on “canonical” evolutionary sequences studying studying ANOMALOUS sequences as Blue Stragglers Stars Blue Stragglers Stars and exotic objects and exotic objects

UV sensitivity, high resolution UV sensitivity, high resolution systematic studies of hot SPs in the core of high density GGCs HST

IBs: Mass transfer binaries in which a WD is accreting material from a Companion through a UV emitting accretion disk MSP companions: He-WD = remnant of the recycling process the recycling process BSS: stars more massive than the stars more massive than the “normal” cluster stars Originated by “coaelescence” of two low mass stars low mass stars(binaries+collisions) Blue Hook HB stars: Hot Helium flashers ? Hot Helium flashers ? (stars ignite He after heavy mass-loss) Normal Helium-rich HB stars? Binaries by-product? Binaries by-product?

? according to their position in the CMD, according to their position in the CMD, BSS should be more massive than BSS should be more massive than normal stars (see also Shara et al 1997) BSS have been detected for the first time by Sandage (1953) merger of 2 low-mass stars merger of 2 low-mass stars unevolved, massive star unevolved, massive star primordialBinaries …evolving in isolation In low density GCs directCollisions..in the central region of high density GCs BSS crucial link between BSS crucial link between stellar evolution & stellar dynamics PB-BSS COL-BSS

<1990 loose GGCs natural habitat low c, low   for BSS >1990 high resolution studies BSS also in the inner region of high density GGCs NGC6397 Auriere et al NGC6397 Auriere et al Tuc Paresce et al Tuc Paresce et al M15 Ferraro & Paresce 1993 M15 Ferraro & Paresce 1993Catalogs: Fusi Pecci et al Fusi Pecci et al Sarajedini et al Ferraro, Fusi Pecci, Bellazzini 1995 Guhathakurta et al. 1994, 1998 Piotto et al 2004 BSS are a common population of GGCs, BSS are a common population of GGCs, found in each cluster properly observed Paresce et al (1991,Nature,352,297)

UV-plane ideal to study UV-plane ideal to study the photometric properties the photometric properties of the BSS population: of the BSS population: - the distribution is almost vertical - span more than 3 magnitudes Ferraro et al (1997,A&A,324,915) Ferraro et al (2001,ApJ,561,337)

305 BSS !! 305 BSS !! The largest population ever observed in a GGC The most concentrated BSS population BSS population ever found in a GGC M80 is the densest, not-PCC cluster of the Galaxy cluster of the Galaxy Log   = 5.8 M s /pc 3

Could the dynamical evolution of the cluster play a role in the formation of BSS? Are collisions delaying the core collapse and the core collapse and generating COL-BSS? generating COL-BSS? Why M80 has such a large population of BSS ? M80 is a quite concentrated cluster (Log   = 5.8 M s /pc 3 ) BUT other clusters with similar concentration like 47 Tuc (Log   = 5.1 M s /pc 3 ) NGC2808 (Log   = 5.0 M s /pc 3 ) NGC6388 (Log   = 5.7 M s /pc 3 ) have many fewer BSS (N BSS < 100) M80 is not a PCC M80 is not a PCC but it should be !!!! but it should be !!!! its dynamical time scale its dynamical time scale is much shorter than its age ! is much shorter than its age ! This would be the This would be the first direct evidence !!!

collapsing N BSS = 129 F = 0.44 – 1.0 PCC? N BSS = 17 F = 0.16 binaries are preventing core collapse ? core collapse ? are binaries destroyed are binaries destroyed during the collapse ? during the collapse ? ?

M 3 Log   = 3.5 M s /pc 3 Log   =  5.8 M s N BSS = 72 F = 0.28 M 13 Log   = 3.4 M s /pc 3 Log   =  5.8 M s N BSS = 16 F = 0.07 twin clusters different primordial binary population ? clusters in different dynamical phases ? ?

Sollima et al (2007, MNRAS, 380,781 ) The Binary fraction in 13 low-density clusters from ACS-HST observations 12-15% 14-19% 11-12% 10-12% 13-17% 16-21% 12-13% 16-22% 16-21% 28-40% 33-50% 51-65% 41-51%

M3 The BSS radial distribution The BSS radial distribution is BIMODAL is BIMODAL

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 Radius of avoidance Important signatures of the dynamical evolution of the parent cluster is imprinted in the BSS properties

V1 Paresce, De Marchi & Ferraro (1992) V2 – Dwarf Nova Paresce & De Marchi (1994) X-ray CHANDRA catalog by Grindlay et al 2001 IBs : LMXB = accreting NS in binary systems LLXGC = acceting WD 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) to the field !!!! (collisional origin)

Dieball et al (2007,ApJ,670,379) Knigge et al (2002, ApJ,579,752) 47 Tuc M15 ONLY the brightest portion of the IB region has been explored!!! An extensive search for IBs in GCs is still lacking: - Which process generate IBs? COL & PB ? COL & PB ? - Are IBs less abundant in the core of high density GCs? of high density GCs? - Are collisions destroying or creating IBs?

1.High resolution 2. UV sensitivity WFC3/UVIS WFC2

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 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

47 TUC Edmonds et al (2001) He WD Fully consistent with the canonical scenario of the MSP recycling process

MSP J in NGC6397 shows eclipse of the radio signal for about 40% of the orbit (D’Amico 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 in the framework of the MSP recycling scenario MSP recycling scenario Ferraro et al (2001,ApJ,561,L93) Star A is the MSP companion ( COMJ1740) ( COMJ1740)

COM J1740 is tidally distorted and is loosing mass from and is loosing mass from its Roche lobe its Roche lobe High-resolution spectroscopic campaign with Ferraro et al (2002,ApJ, 584,L13) & Sabbi et al (2003, ApJ,589,L41) Burderi et al (2002) suggested that the position of COMJ1740 in the CMD is consistent with the 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 Mass=0.3 Mo !!!!! This bright object is the ideal target for Spectroscopic follow-up.

No C in the COM J 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) COMJ1740 has the same overall chemical composition of the SGBs SGBs COMJ1740

U in 47 Tuc: 0.2 Mo He-WD Edmonds et al (2001) COMJ in NGC6397: 0.3 Mo (pre He-WD) 0.3 Mo (pre He-WD) Ferraro et al (2001) W in 47 Tuc: 0.13 Mo MS Edmonds et al (2002) COMB in M4: 0.3 Mo He-WD Sigurdsson et al (2003) COMJ in NGC6752: 0.2 Mo He-WD 0.2 Mo He-WD Ferraro et al (2003),Bassa et al (2003) 6 objects in 5 GGCs: 3 are HeWDs + 2 pre HeWD CO-WDHe-WD COMJ B in NGC6266: ?? Mo (pre He-WD) ?? Mo (pre He-WD) Cocozza et al (2007)

All the MSPs discovered so far in NGC6266 are in binary systems 6 MSPs have been discovered in this cluster by D’Amico et al (2001a,b) and Jacoby et al (2002) + 51 X-ray sources (Pooley et al 2002) Relatively nearby cluster (7 Kpc) High reddening GC E(B-V)=0.48 E(B-V)=0.48 ( with some differential reddening ) This cluster could be in a dynamical phase particularly active in generating COL-binaries

33 MSPs have been discovered in TERZAN 5 : this is the largest population of MSP ever detected in a GC 17 MSP are in binary systems: most of them with a massive (>0.2 Mo) companion PC WFPC2 NICMOS

1.High resolution 2. High sensitivity in the IR WFC3/IR NICMOS/NIC3

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 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

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 (c=1.8) King profile, with power-law deviation at the very center:  (r) ~ r -0.2 at r < 0.1 r c [PCC clusters: c > 2,  (r) ~ r -0.8 ] 2) sharp rise in the central velocity dispersion profile (at r < 0.05 r c ) 3) presence of few high-velocity (even v ~ 100 km/s) stars + possible X-ray and radio emission from accreting gas

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. 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 c = 1.8 r c = 7.2” M BH ~ M o

NGC 6388 Determination of the centre V < 20 (~ 4000 stars) ~2.6” south-east of the DM93 centre  J2000 = 17 h 36 m s  J2000 = -44 o 44 ’ 7.1 ” ,  ~ 0.2”-0.3”

1.ULTRA-ACCURATE SB & SD profiles for the promising clusters High resolution (ACS/HRC) +WFC3/UVIS 2.MULTI-EPOCH HR images of the center & Accurate proper motion (a few MAS) measures to detect High velocity stars (v>100 Km/s) 1.High resolution 2. Large field of view