The Effect of Blue Stragglers on the Integrated Light of Stellar Populations

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The Effect of Blue Stragglers on the Integrated
Light of Stellar Populations

• Bob Rood with the assistance of Ricardo Schiavon
  and Francesco Ferraro

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None!
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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
primordial binaries
direct collisions
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Blue Straggler Stars
lt1990
gt1990
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HST
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M79 with GALEX FUV - NUV
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M3 The first surprise
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Blue Straggler Stars M3
The BSS radial distribution is
BIMODAL
Highly peaked in the center rapidly
decreasing at intermediate radii and finally
rising again at larger radii
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BSS radial distribution
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The BSS bimodal distributions
?
collisional BSS _at_ center PB-BSS in the outer
regions?
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BSS radial distribution
v Centauri NO evidence of mass segregation!!!!
The purest population of not-collisional BSS?
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Direct comparison of BSS populations
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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 ?
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Blue sequences in the UV
direct comparison of BSS populations
Log r0 2.1 Ms/pc3 NBSS 24 F 0.92
!!! the largest specific frequency ever observed
in one of the lowest density cluster
Log r0 5.8 Ms/pc3 NBSS 129 F 0.44 F
1 if only the PC is considered
?
different types of BSS ?
NGC288 has a large fraction of binaries !
Bellazzini et al. 2002 AJ, 123, 1509
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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 ?
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BSS radial distribution
v Centauri NO evidence of mass segregation!!!!
The purest population of not-collisional BSS?
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Among the GCCs ? Cen is the best BSS template
NBSS ? 0.08 NHB NBSS/104L? ? 2
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Peterson et al. 2003, ApJ, 588, 299.
The real problem NBSS ? 7 NRG
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In the visible BSS and cool BHB are equivalent
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Schiavon et al. 2002
47 Tuc
BSS contribute lt1 to the integrated light of 47
Tuc
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Deng et al. 1999 ApJ, 524, 824
M67
Note NBSS ? 4 NHB
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Schiavon, et al 2004, ApJ, 127, 1513
M67
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Schiavon BSS greatly increase Balmer line
strengths
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M67 in the UV (Landesman et al. 1998)
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F81
Other BSS
Non-BSS
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With BSS 2.5 Gyr model
Without BSS 4.5 Gyr model
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How much has dynamical evolution affected M67?