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Globular Clusters: HST Breathes New Life into Old Fossils

1. Globular Clusters: HST Breathes New Life into Old Fossils. Hubble Science Briefing Jay Anderson STScI June 3, 2010. 2. Outline. Globular Clusters Omega Cen Early release images Colors Simulations Stellar Populations The cutting edge with HST. 3. Globular Clusters.

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Globular Clusters: HST Breathes New Life into Old Fossils

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  1. 1 Globular Clusters: HST Breathes New Life into Old Fossils Hubble Science Briefing Jay Anderson STScI June 3, 2010

  2. 2 Outline • Globular Clusters • Omega Cen Early release images • Colors • Simulations • Stellar Populations • The cutting edge with HST

  3. 3 Globular Clusters • “Textbook” simple stellar populations • Formed stars early • Single cloud, single metallicity, single age • Not large enough to self-enrich • Continue orbiting in spheroid of Galaxy • Perfect laboratories to evaluate stellar evolution

  4. 4 OMEGA CEN EARLY-RELEASE IMAGE History of this image 1) Why taken? 2) Why ERO? 3) Why “saturated” ?

  5. Hubble: one Filter at a time 5 Familiar digital cameras: all at once James Webb ST: two at a time

  6. 10x10 ACS 6 Early Release Field Central Field

  7. 7.1 The central field… RGB

  8. 7.2 The central field… Blue

  9. 7.3 The central field… Red

  10. 7.4 The central field… RGB

  11. 8 HUBBLE IMAX:MAYA was used to render the scene in 3-D

  12. The PSF 9.1 Decomposing the image… “a point source has no hair” Real close up wide view

  13. The PSF 9.2 Decomposing the image… “a point source has no hair” Simulated close up wide view

  14. 10.1 What Astronomers see…

  15. 10.2 What Astronomers see…

  16. 10.3 What Astronomers see…

  17. 10.4 What Astronomers see…

  18. 10.5 What Astronomers see…

  19. 10.6 What Astronomers see…

  20. 10.7 What Astronomers see…

  21. 10.8 What Astronomers see…

  22. 10.9 What Astronomers see…

  23. 10.10 What Astronomers see…

  24. 10.11 What Astronomers see…

  25. 10.12 What Astronomers see…

  26. 10.13 What Astronomers see…

  27. 10.14 What Astronomers see… 3) Red Giant Branch 4) Horizontal Branch 5) White Dwarf Sequence 1) Main Sequence 2) SubGiant Branch

  28. 11 Easy to identify stars… RGB HB SGB BSs MSTO WDs Red Dwarfs

  29. “Isochrone” 12 Stellar Populations Red Giant Branch C Globular clusters have traditionally been defined as textbook “simple” stellar populations: bound clusters of stars at the same distance, with the same age, and the same metallicity.  same small cloud More metals Age B A More Helium

  30. Omega N6397 47T Omega Cen NGC6397 47 Tuc Extra sequences 13

  31. Globular Cluster or Dwarf Spheroidal? Cambridge, UK 2001 14

  32. 15 Stellar Populations Red Giant Branch metal poor intermediate metal rich More metals Age More metals Inversion! More Helium Similar to galaxies…

  33. 16 Is Omega Cen a GC? Could the textbook globular cluster not be one? ® OmCen Pluto 47Tuc N2808 N6388 N6656

  34. 17 Is Omega Cen a globular? Are there any globular clusters? Questions to answer: How do clusters enrich themselves? Why are they all so different? Is it all clusters, or just heavy ones? What connection is there between clusters and galaxies? 5) Any relevance for star formation going on today? NGC6652 NGC2808

  35. 18 More HST with Clusters… • HST’s advantages • Resolution: separate stars • Lower background: concentrate star, not sky • Stability: no atmosphere, same PSF • UV and IR coverage • Proper motions: 1) Cluster-field separation 2) Search for black holes

  36. 19 The first full CMD Bright • Richer et al. 2005 observed NGC6397 with 126 orbits • Discoveries • End of WD cooling seq • Blue hook at bottom! • End of MS? • Limitations: field stars WDCS HBL? Faint Red Blue

  37. 20.1 PI-Rich, UCLA Proper-Motion Cleaning

  38. 20.2 PI-Rich, UCLA Proper-Motion Cleaning

  39. 20.3 PI-Rich, UCLA Proper-Motion Cleaning

  40. 20.4 PI-Rich, UCLA Proper-Motion Cleaning

  41. 21 Intermediate-Mass Black Holes (IMBHs) in GCs • BHs known to exist with • ~10 MSUN : HMXBs • ~106 MSUN: SMBHs at centers of galaxies • ~104 MSUN: IMBHs? • Could help explain how SMBHs grow • ULXs in other galaxies • M relation… 10,000 MSUN Greene & Ho (2006) ~20 km/s

  42. 22 IMBHs in Globular Clusters II • Several ways to find (PMs or RVs) • Fast moving star in orbit (smoking gun) • Rise in velocities at center • Also pulsars, accretion signatures, certain cusps • Several ways to not find • Not enough stars/gas to sample its environs • Nearby stars all dark, ejecting binaries • Easiest places to look: • Clusters with cusps & slow velocities • Zone of influence rBH ~MBH/2 • Omega Cen is not the easiest place to look… Yet…

  43. 23 Current evidence? • Detections/limits in the literature • M15: back and forth; currently not required… • NGC6752: negative P pulsars: 1000 MSUN • 47 Tuc: upper limit of 1500 MSUN • G1 in M31? X/Radio emission and velocities •  Cen circumstantial evidence: • Noyola, Gebhardt & Bergmann 2008 (NGB08) 1) Detected a brightness cusp at center in ACS images 2) Used an IFU at Gemini and saw a velocity spike there Could be explained by a 40,000 MSUN IMBH • This dispersion increase should be detectable with HST PMs…

  44. 24 MeasuringProper Motions Epoch1: 2002 Epoch2: 2006

  45. Stars with good measured motions 25

  46. 26. 1

  47. 26. 2

  48. 26. 3

  49. 26. 4

  50. 26. 5

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