in the Milky Way Christian Johnson Smithsonian Astrophysical Observatory Typical Globular Clusters Main Sequence Main Sequence Turnoff Subgiant Branch Red Giant Branch Horizontal Branch ID: 553103
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Slide1
Peculiar Massive Globular Clusters
in the Milky Way
Christian Johnson
Smithsonian Astrophysical ObservatorySlide2
“Typical” Globular Clusters
Main Sequence
Main Sequence Turn-off
Subgiant Branch
Red Giant Branch
Horizontal Branch
Asymptotic Giant Branch
Stars exhibit small or negligible age spread
Very small (< 12%) metallicity dispersion
Simple Stellar Population
Globular Cluster M13
B
B-I
Sandquist
+ (2010)Slide3
Modern Picture of Globular Clusters
Carretta
+ (2009)
Piotto
+ (2015)
Gratton
+ (2004)
Johnson+ (2017, in prep.)
α-enhanced → rapid enrichment r-process comp.→ rapid enrichment Slide4
ω
CenM 54
NGC 6273
Da Costa (2015)
[Fe/H] dispersion not yet measuredMass
M 2
M 22NGC 5286A subset of the most massive globular clusters in the Milky Way have significant star-to-star [Fe/H] Variations
Peculiar Massive Clusters
NGC 6273Slide5
Signatures of Peculiar Massive Clusters
Johnson+ (2010)
Johnson+ (2016)
Marino+ (2015)
NGC 5286
Carretta
+ (2010)
Johnson+ (2015)
Yong+ (2014)
Metal-poor
Metal-intermediateSlide6
Signatures of Peculiar Massive Clusters
Johnson+ (2010)
Bellini+ (2009)
ω
Cen
Distinct stellar groups with different [Fe/H] values
BHB
Han+ (2015)
NGC 6273
Marino+ (2015)
NGC 5286Slide7
Metal-poor
Metal-intermediateMetal-rich
Johnson+ (2016)
Light Element Variations
Marino+ (2011)
Metal-poor
Metal-rich
The same light element abundance (anti-)correlations observed in monometallic clusters is also present in each sub-population of all iron-complex clusters
Some clusters exhibit abundance pattern changes with [Fe/H]…
NGC 6273
M 22Slide8
Light Element Variations
Metal-poor
Metal-int.
Metal-int. 2
Metal-rich
Johnson+ (2016)
Johnson+ (2010)ω CenNGC 6273Changes in the light element abundance correlations may signify new pollution sources and/or burning temperatures
> 65 MK
< 65 MKNot seen in other clustersSlide9
Alpha Element Variations
Carretta+ (2010)
M 54 Cluster Stars
Sagittarius
dSph field stars
The M 54 + Sag. dSph system exhibits different [
α/Fe]; cluster stars are α-enhanced and field stars have lower [α/Fe]Slide10
Alpha Element Variations
Johnson+ (2016)
Pancino
+ (2002)
Yong+ (2014)ω Cen
NGC 6273M 2Slide11
Heavy Element Variations
Pure s-process
McWilliam
(2011)
Marino+ (2015)
Johnson+ (2016)
ω
CenNGC 6273Slide12
ω
Cen
M 54
NGC 6273
Da Costa (2015)
[Fe/H] dispersion not yet measured
MassM 2
M 22
NGC 5286Final ThoughtsThe most massive and complex clusters may have been former dwarf galaxy cores and may be identified by their chemical compositions