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Exotic populations in

Bologna, January 29, 200 8. Exotic populations in. Galactic Globular Clusters. Francesco R. Ferraro. Dip. di Astronomia - Univ. di Bologna (ITALY). ASTRO – ARCHEOLOGY TRACERS of the structure & history of the Galaxy. ASTRO – TIMING LABORATORY for theoretical models

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Exotic populations in

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  1. Bologna, January 29, 2008 Exotic populations in Galactic Globular Clusters Francesco R. Ferraro Dip. di Astronomia - Univ. di Bologna (ITALY)

  2. 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

  3. 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

  4. by-products of binary systems “perturbing” effects on “canonical” evolutionary sequences studying ANOMALOUS sequences as Blue Stragglers Stars and exotic objects Exotic populations in the CMD UVE

  5. UV sensitivity , high resolution systematic studies of hot SPs in the core of high density GGCs The "classical" plane The UV plane HST

  6. Blue Hook HB stars: Hot Helium flashers ? (stars ignite He after heavy mass-loss) Normal Helium-rich HB stars? Binaries by-product? 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 BSS: stars more massive than the “normal” cluster stars Originated by “coaelescence” of two low mass stars (binaries+collisions) Exotics in the UV

  7. merger of 2 low-mass stars unevolved, massive star BSS crucial link between stellar evolution & stellar dynamics 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

  8. loose GGCs natural habitat low c, low r0 for BSS • high resolution studies • BSSalso in the inner region • of high density GGCs • NGC6397 Auriere et al. 1990 • 47 Tuc Paresce et al. 1991 • M15 Ferraro & Paresce 1993 • Catalogs: • Fusi Pecci et al. 1992 • Sarajedini et al. 1992 • Ferraro, Fusi Pecci, Bellazzini 1995 • Guhathakurta et al. 1994, 1998 • Piotto et al 2004 Blue Straggler Stars <1990 >1990 Paresce et al (1991,Nature,352,297) BSS are a common population of GGCs, found in each cluster properly observed

  9. BSS in the UV: UV-planeideal to study the photometric properties of theBSS 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)

  10. 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 aGGC The most concentrated BSS population ever found in a GGC

  11. 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(NBSS< 100) Could the dynamical evolution of the cluster play a role in the formation of BSS? M80is 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 !!!

  12. 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 ?

  13. 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 ?

  14. 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)

  15. The BSS radial distribution is BIMODAL M3

  16. 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

  17. 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)

  18. 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)

  19. What do we need? High resolution 2. UV sensitivity WFC2 WFC3/UVIS

  20. Exotic stellar populations: the MSP companions

  21. 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

  22. 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)

  23. The bright companion to the MSP in NGC6397 MSP J1740-5340 inNGC6397 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 COMJ1740is NOT a WD as expected in the framework of the MSPrecycling scenario Star Ais the MSPcompanion ( COMJ1740) Ferraro et al(2001,ApJ,561,L93)

  24. The bright companion to the MSP in NGC6397 COM J1740is tidally distorted andis 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@VLT Mass=0.3 Mo !!!!! Ferraro et al(2002,ApJ, 584,L13) & Sabbi et al (2003, ApJ,589,L41)

  25. SGBs COMJ1740 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)

  26. The bright companion to the MSP in NGC6397

  27. 6 objects in 5 GGCs: 3 are HeWDs + 2 pre HeWD 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)

  28. Relatively nearby cluster (7 Kpc) High reddening GC E(B-V)=0.48 (with some differential reddening) This cluster could be in a dynamical phase particularly active in generating COL-binaries MSPs in NGC6266 (M62) 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) All the MSPs discovered so far in NGC6266 are in binary systems

  29. 17 MSP are in binary systems: most of them with a massive (>0.2 Mo) companion 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

  30. What do we need? High resolution 2. High sensitivity in the IR NICMOS/NIC3 WFC3/IR

  31. 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

  32. 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 rc [PCC clusters: c > 2, (r) ~ r -0.8 ] 2)sharp rise in the central velocity dispersion profile (at r < 0.05 rc) 3)presence of few high-velocity (even v ~ 100 km/s) stars +possible X-ray and radioemission from accreting gas

  33. 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

  34. NGC 6388 J2000= 17h 36m 17.23s J2000= -44o 44’ 7.1” ,  ~ 0.2”-0.3” ~2.6” south-east of the DM93 centre Determination of the centre V < 20 (~ 4000 stars)

  35. 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 (v>100 Km/s)

  36. The End

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