1. 25 Years of Globular Clusters with HST
Hubble Science Briefing
Jay Anderson
STScI
March 4, 2015

2. Plan (1) Globular Clusters before HST (2) Globular Clusters with HST
(3) Globular Clusters with 25 years of HST

3. Globular Clusters “Textbook” simple stellar populations Perfect fossil
Formed stars early
Single cloud, single metallicity, single age
Not large enough to self-enrich
Continue orbiting in spheroid of Galaxy
Perfect fossil
laboratories
to evaluate
stellar evolution GC GC GC GC GC
NGC4013(NOAO)

4. Central
Field
project-nightflight.net
ω Centauri
Early Release
Field

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

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

8. Stellar Populations “Isochrone” One line means: same age
Red Giant
Branch C
More
metals
One line means:
same age
same metallicity
same distance
 same small cloud
Age B A
“test of good photometry”
More
Helium

9. Omega N T
Omega Cen
NGC6397
47 Tuc
Extra
sequences

10. Plan (1) Globular Clusters before HST (2) Globular Clusters with HST
(3) Globular Clusters with 25 years of HST

11. Globular Cluster or Dwarf Spheroidal?
Cambridge, UK 2001
Globular Cluster or Dwarf Spheroidal?

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

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

14. Is Omega Cen a globular? Are there any globular clusters?
Questions to answer:
How does the enrichment happen?
Why are they all so different?
What connection is there between
clusters and galaxies?
4) Any relevance for star formation
going on today?
NGC6652
NGC2808

15. Plan (1) Globular Clusters before HST (2) Globular Clusters with HST
(3) Globular Clusters with 25 years of HST

16. GCs with Hubble Over Time
Set up new experiments
Probe deeper
Probe more broadly
Use new detectors
Better sensitivity, resolution
Better filter sets
Things move!

17. ω Centauri Anderson et al 2002 Bellini 2014 (WFC3/UVIS)
Initial 2-seq Discovery on
Main Sequence (WF/PC2)
Bellini 2014 (WFC3/UVIS)
Latest results all over the diagram! 10 Seqs!

18. NGC2808 Bellini et al in prep (WFC3/UVIS) D’Antona 2005 (ACS)
Initial Discovery

19. Motions in ω Centauri
2002 ACS H-alpha

20. Motions in ω Centauri
2015 WFC3/UVIS F606W

21. MOTIONS OVER 13 YEARS
Motions in ω Centauri
2015 WFC3/UVIS F606W

22. Proper Motions Important Qs Formation hints
Are GCs just little galaxies?
Do they have medium-sized BHs?
How did the big BHs form in big galaxies?

23. Plan (1) Globular Clusters before HST (2) Globular Clusters with HST
(3) Globular Clusters with 25 years of HST
(4) Globular Clusters in the next 25 years..