Why do globula clustes have moe than one main sequence? Ref: Gatton et al. 2012, A&ARv, 20, 50
1 st, a petty pictue
Outline The lives of stas Some basic physics Impotance of clustes Globula clustes ae eally, eally old! GC details Obsevations GC details Models and fomation
Lives of Stas What do we know about stas? They ae bon They live They die They spead thei seed
Stas appea in goups Lives of Stas
Modeling a Sta 2 ) ) ) GM d dp ) 4 ) 2 d dm 3 2 ) 4 4 ) ) ) 3 ) act L d dt ) ) 4 ) 2 d dl * * * ) 0 ) 0 0) 0 0) M M P L M Fou coupled fist-ode diffeential equations descibe stella stuctue
Physics of Stas Need a way to connect: pessue, opacity, and enegy poduction ),, ),, ),, composition T composition T composition T P P Equation of State 4 3 1 ~ at m kt P P P ad g Opacity 3.5, T ff bf Enegy geneation 3 1 3 2 6 1 0 2 3 5 4 3 exp ) 3 2 2 kt E kt E QS A A m X X G G B A H B A
Sta clustes Open Cluste Globula Cluste
Stella evolution Ou ideas of stella evolution came about because of the single population theoy of cluste fomation. But thee ae still some outstanding issues Blue staggles Mass loss AGB stas White dwaf cooling
Why ae clustes impotant?
Oveview of sta fomation Tigge Gavitational collapse Heating/otation/magnetic fields slow collapse Eventual H-fusion Main sequence sta
OB association fomation
Globula clustes Spheical collection of gavitationally bound stas > 100,000 stas The Milky Way has about 200 GCs ae found in all galaxies of lage size
Othe galaxies M87 Moe than 10,000 GCs Many visible in this image
1 Main sequence Photometic naow MSs Poof of single-age Single metallicity Until
47 Tuc 16,700 ly away 120 ly acoss M V ~ 4.9 ~ full moon size
47 Tuc Single MS? Cannon et al. 1998
47 Tuc Anticoelation between CN and CH molecula bands
47 Tuc Why is this impessive? Pimodial in oigin Giant stas can mix N MS stas can not! Anticoelations between O and Na & Mg and Al Low mass stas do not make Na No do they destoy Mg Clea indication of extenal oigin
ω Cen 15,800 ly away 180 ly acoss ~ million M suns Coe stas.1 ly fom each othe
ω Cen 2 o 3 MSs Bedin et al. 2004
NGC 2808 Typical GC 31,000 ly away ~12.5 Gy old
NGC 2808 Tiple MSs Piotto et al. 2007
Not just MSs Red giant banches of HR diagams contain multiple populations of stas Hoizontal banches of HR diagams too.
GC Fomation Undestanding of the multiple population phenomenon has changed Oiginally Few peculia clustes Only massive clustes Now Pobably all GCs have multiple populations
If 1-population theoy wong GCs fomed within lage episodes of sta fomation in Giant Molecula Associations Scenaios include seveal geneations of stas Pimodial, fist, second We obseve second geneation now Fist geneation polluted the second
4 additional mechanisms to conside Oiginal homogeneities in the pimodial mateial Peculia evolution of stas Meging of GCs GC pulling in intestella mateial pollution )
A possible model N-body & hydo. simulations 1 st geneation AGB sta s ejecta flows to GC cente 2 nd geneation foms with diffeent metallicity Concentated at cente of GC Poblem: IMF eithe uncommon o unknown
A sticky detail The polluting ejecta must be diluted by fesh gas Mandatoy pat of the pocess Poblem: how much of oiginal gas went to 1 st geneation? Poblem: how is pistine mateial gatheed?
GC Milky Way connection Pesent day GCs smalle now Sta loss duing initial fomation Poblem: what ole does dak matte play?
Mass of GCs GCs used to be lage Oiginal poto-gcs contained 50% of halo mass Of all stas in halo 1.2% ae in GCs Othe 98.8% ae fee but ae in a HUGE volume
Lingeing questions Mechanisms of inhomogeneities Natue of pollutes Nucleosynthesis mechanisms Oigin of diluting mateial Reliable 3-D hydodynamical models of fomation
my Contibution I model 2 aspects of this poblem Mean opacities necessay fo stella evolution Atmosphee models necessay fo colo-colo diagams
Example NGC 6752 M V ~ 5.4 Age ~ 11.8 Gy ~ 17,000 Ly
2 atmosphee models compaed Dotte et al. 2015, MNRAS, 446, 1641
Anothe petty pictue
dsphs? Ae GCs just small dwaf spheoidal galaxies? GCs ae close to main MW GCs lost dak matte dsphs did not) GCs ae compact dsphs evolved in isolation GCs ae pat of MW)