NGC 2419 – the most bizarre Galactic globular cluster

Judith Cohen (Caltech) & Evan Kirby (UC Irvine/Caltech)

Conference: Small Stellar Systems,Tuscany, Italy June 2013

Nucleosynthesis of elements

• How to use chemical inventory to infer GC history

• a-elements, abundant, N 4He, SNII• Light elements C,N,O,Na,Mg,Al,(Si) AGB

stars /rapidly rotating massive stars• Fe-peak elements SNIa• Heavy neutron capture elements (Sr,Y,Zr vs

Ba….Eu..Dy) r (SNII) and s(AGB)

Multiple Stellar Generations

• Variations of He,C,N,O,Na,Mg,Al, (Si) do NOT require SN contribution after initial burst

• Variations of heavier elements up to end of Fe-peak DO require additional SN input

• Variations of s-process n-capture elements do NOT require additional SN input

• Variations of r-process n-capture elements DO require additional SN input

NGC 2419 (Cohen & Kirby)

• ~85 kpc from Sun at b = 25.2 deg• Luminous cluster MV -9.6 mag, most luminous

of all GCs with R > 20 kpc, of all R > 15 kpc except for M54

• Largest core and half light radius of any GC in the outer halo of the Milky Way

• HST imaging – no evidence for a spread in age/metallicity, but does have an extremely blue extension of the HB (Di Criscienzo et al, 2012)

R(h) vs M_V, (Van den Bergh & Mackey, 2005)

NGC 2419: Anomaly is in L, not in R(h)(McLaughlin 2000)

Deimos GC Project of Cohen & Kirby

• Clusters checked with Deimos spectra (mod res, 6000 to 10,000 A)

• NGC 2419, NGC 4590 (M68), NGC 5024 (M53), NGC 5053, NGC 5634, NGC 5904 (M5), NGC 6205 (M13), NGC 6229, NGC 6341 (M92), NGC 6656 (M22), NGC 6838 (M71), NGC 7006, NGC 7078 (M15), NGC 7089 (M2)

• Only NGC 2419 and M22 (MV -8.50) show signs of a spread in Ca/H. M22 is most obvious of the 2.

M15, NGC 2419, M5 Deimos CaT vs V-V(HB)

NGC 2419 new HIRES sample on Ca/H histogram

NGC 2419 Cohen Kirby abundances vs V mag

NGC 2419 Cohen & Kirby 2013 normal Mg/Blue, low Mg/red

NGC 2419 Cohen & Kirby 2013 normal Mg/blue, low Mg/red

NGC 2419 Ca/H (HIRES) vs Ca/H(CaT Deimos)

Summed spectra of Mg-poor (blue) and Mg-rich (red)

Summed spectra NGC 2419 RGB Mg-poor/rich

Summed spectra NGC 2419, Mg poor/rich

Summed spectra: Mg-normal blue, Mg-poor red

Trends with [Na/Fe] in NGC 2419 HIRES sample

Status – NGC 2419

• NGC 2419 unique and bizarre, showing a normal metal-poor GC population plus one with Mg , K Sc , and modest Ca enhancement. Fe range is not detected.

• Ventura et al (2013): HBB in unusually massive AGB stars maybe can do this – not easily though. Need T > 108 requires M ~ 6 Msun.

• Test: C and especially O abundances

NEW: Carbon abundances (Deimos/Keck, Cohen)

NEW: [C/Fe] vs V (Deimos/Keck: Kirby)

M13 [C/Fe] vs V. v line=RGB bump, tip~12.2, MSTO ~ 18.5 Briley, Cohen, Harbeck 2008, never published

NEW: [C/Fe] vs V (Deimos/Keck)

NEW: Carbon abundances Deimos/Keck

Summary

Many GCs show no evidence for a range in heavy elements (Ca,Fe peak) - would require SN contribution

Essentially all show well known correlations among light elements AGB or rapidly rotating massive stars

Some of these show associated s-process enhancements

Only M92 shows enhanced r-process

Most massive often show range of Ca, Fe, etc andare probably remnants of accreted satellites with more complex extended star formation history than in normal GCs.

Today: NGC 2419 still unique

• C/Fe appears normal for a GC (trend with M_V and spread at a given M_V)

• Possible that Mg-poor stars have slightly higher mean [C/Fe] than Mg-normal

• Mean difference in [C/Fe] vs V is only ~0.2 dex.

• Working towards O abundances, soon…

Small Stellar Systems, June 2013, Tuscany, Italy

BACKUP SLIDES

NGC 2419

red [Mg/Fe] < 0, bl > 0

iso. 12 Gyr,

[Fe/H] -2.2, -1.9

Mg e-

donor.

Impact of change in Mg on atmos-phere shown

here, also impact on

CMD.

Diagnostic diagrams of abund vs V mag and of ion eq for Fe and for

Ti

HIRES sample

NGC 2419 13 RGB

stars

NGC 2419 Spatial distribution (high Ca - red)

NGC 2419 – emission in wings of H , a indicator of extended atmosphere, mass loss, chromosphere

NGC 2419 summed spectra, no sign of Li 6707

C depletion vs age in Myr with 0.0 = RGB tip (M13 filled, M15 open, RGB bump to tip), f 0.023 (0.035) dex/Myr

M92 rare earths, abundances are

constantCohen, 2011,

ApJL, s=0.06 to 0.07

dex for Fe, Y, Ba, La, and Eu/Fe

M15 r-process,

rare earths are r-proc, with X/Fe varying by

factor of 6 !J.Cohen,

2008, never published

M15 – compare

[X/Fe](obs) vs s-process

ratios.

Not s-process !

No detectable range in Fe/H within 19 GCs, UVES (high res, few stars) & Giraffe (mod res, many stars) Carretta et al (2000)

Ca/H distribution from RGBs in 19 GCs show no detectable range within a GC Carretta et al (2001)

Internal range in Fe seems to be confined to the

most massive (as seen today) GCs

(Carretta et al 2010)

NGC 1851, Yong et al,

Carretta et al, 2011

MV -8.33 mag

NGC 1851, high Fe/H = high Ba/H, s-process, Yong et al, Carretta et al (2011)

NGC 1851 (Carretta et al), M5 & M4 (Ivans et al), Ba/Eu ratio implies s-process enhancement

M71 precision abunds (Melendez& Cohen 2008)

M71 Mg isotopic ratios, s-process, Melendez & Cohen (2008)

M71

Note v low s in X/Fe for

all except La/Fe