Peculiar abundance patterns in
Galactic bulge stars

Andreas Koch

C.J. Hansen (DARK); M. Hampel (LSW)D. Martin, A. Arcones (TU Darmstadt)
A. Karakas (Monash)“Neutron star mergers: From gravitational waves to nucleosynthesis“, Hirschegg, Jan. 20, 2017

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Galactic Components

M104 (HST) – unbarred spiral with ca. 40% x mass of MW

Disk(s)
Halo: stars, globular clusters, satellite galaxies, dark matter
Central bulge (bars)
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Halo formation
ΛCDM: hierarchical halo formation via accretion of dark matterdominated fragments.
Metal-poor halo stars wereprobably donated from satellite
accretion.
Some stars in the dwarf satellites
show chemical imprints fromindividual events (à Pop III).
à clues to the earliest
enrichment phases.
Bullock & Johnston (2005)

What about the bulge?
AK et al. 2008; Tolstoy et al. (2009); Simon et al. (2010); AK & Rich (2014)

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Bulges- 25% of the light in the local universe comes from bulges.
- Inhomogeneous class of objects with different formation
channels:1) Spheroidal (“classical”) bulges form rapidly via earlymergers. Bulge forms before disk.
2) Pseudo-bulges / bars evolve from a buckling instability
over longer timescales (>1 Gyr).

NGC 4710 (HST); McWilliam & Zoccali (2010); Rich (2012)

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(Galactic) bulge formation• The bulge is old and metal rich, yet very complex(e.g., McWilliam & Rich 1994; Clarkson et al. 2008; Bensby et al. 2013).

• Dynamical formation, where bulge == bar (e.g., Shen et al. 2010;
Wegg et al. 2015) ? Prominent X-shape (McWilliam & Zoccali 2010)• No evidence for kinematic substructures (streams).
(e.g., Howard et al. 2008; Kunder, AK, et al. 2012; Kunder et al. 2014, 2015;
C.J. Hansen, AK, et al. 2016).

Wegg et al. (2015)

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Bulge vs. halo formation• Oldest stars with [Fe/H] < −3 (z > 6 - 10) are predicted ontight orbits in the innermost halo, due to inside-out natureof CDM: "In the bulge, not of the bulge" (Tumlinson 2010).
• E.g., ARGOS bulge survey: non-rotating, metal-poor tail;attributed to the inner halo (RGC < 3.5 kpc; Ness et al. 2013).
See also BRAVA (Howard et al. 2008; Kunder, AK, et al. 2012).

250946 bulge RR Lyrae

To date: 55 stars in high-res
between -2 and -4 dex in surveysof several 10000s stars(Kunder, Rich, AK, et al. 2016)

N200150100(Ness et al. 2013; García Pérez et al. 2013;
Howes et al. 2014, 2015; Casey & Schlaufman 2015,AK et al. 2016)

500−4−3−2[Fe/H]−106/15

[Cr/Fe]

0.5

Abundance results[Mn/Fe][Ba/Fe]−0.5
0.53High-resolution
spectroscopy of seven bulge stars (AK et al. 2016)
201 majority of (23) species is compatible with theThe−0.50−1−10.830.50.4
2
Metal-poor Halo (Roederer et al. 2014)
0100−0.5α-element−1Bulge (Johnson et al. 2012, 2014)−0.4[Co/Fe][Ca/Fe][La/Fe]halo !

[Fe/H][Ni/Fe][Sc/Fe][Nd/Fe]0.5
0.4
20100−0.5−0.4
1−1320.5211000−1−0.5−10.532010−0.5

Metal-poor "bulge" (Casey & Schlaufman 2014;
Howes et al. 2014)

Fe-peak−3−2[Ti/Fe][Eu/Fe][Ba/Fe][V I/Fe][La/Fe]••0−1[Fe/H]

0n-capture−3−2−1[Fe/H]

This work (AK et al. 2016)

Bulge r-II star (Johnson et al. 2013) at [Fe/H] = -1.67
à (SNe / NSM) r-process polluters are also
active in the bulge!
r-process seems universal

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Normal halo-(like) stars• The majority of (23) species is compatible with the haloand points to standard enrichment processes !

1.5

Mean abundances of all stars
compared to Solar r/s pattern(Simmerer 2004).

10.5log0HD 122563, weak r-processstar (Honda et al. 2004)−0.5−1−1.5−235

Pure sSolar r+s
Pure r404550Z556065

AK et al. 2016, A&A
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Some special guests• one CEMP-s ( [Fe/H] = -2.5, [C/Fe] = 1.4, [Ba/Fe] = 1.3)
• one CH-star ( [Fe/H] = -1.5, [C/Fe] = 0.4, [Ba/Fe] = 1.3)
CEMP-s abundances indicate origin of C-enhancement fromAGB transfer.
First contenders of this class towards the bulge.
1000

1.6

900

1.4

800

1.27001log epsilon& sample spectrum
Flux

600
500
400

1.4 M⦿ AGB model(Lugaro et al. 2012)

0.80.60.4300

0.2200010005130

5140

5150

5160
5170
Wavelength [A]

5180

5190

5200

-0.2
35404550
Z

5560

65

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Special star #10464
CH- / Ba-star ([Fe/H] = -1.5):• Low-metallicity AGB models yield a poor fit for any mass
(e.g., ~1.3 M¤ vs. ~4 M¤ progenitor).
RbBa

2M

Ndooo

6 Mo

30

Zr

35

40

low-Zn

low-Y

Eu

4550
Z

F.R.U.I.T.Y. (Cristallo et al. 2011)

55

60

65AGB

Sr

0.50LaSmmass[X/Fe]AGB

1high-mass

4Ms AGBhigh-mas3M

Each predicts various trends,
at odds with the observations:
AGB

1.3 Mo

mass

1.5

SrZr
SNY

Many problems remain,mainly a very high [Rb/Fe] !

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s-, i-, r- ?
83Bulge rII-star(Johnson et al. (2013)[Fe/H] = -1.67

2.5
7s-processfrom AGBX

log
log epsilon
epsilon

625
1.5
4X

i-processNn ~ 1012–15 cm-331

Herwig et al. (2011):
log Nn = 15 = const.
τ = 46 mb-1

20.5
100-0.5-1-2-1

Hampel et al. (2016):
log Nn = 12τ = 495 mb-1 = const.
30 10204030 50 40

5060
ZZ60 70 708080

C. Ritter: 35 elements in the bulge star #10464 (AK et al. 2016; AK et al. 2017, subm.)

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r-enrichment ?
3AGB s-process+2.5(Models by D. Martin,A. Arcones)

2log epsilon

1.5• 17% jet-like SN II(Ye = 0.2)

1

0.5

0-0.5-1

r-process30354045505560Z65707580•

6% dynamicalejecta (Ye = 0.1)

•0% ν-driven windin NSM

Decomposition ala
C.J. Hansen, Montes,
Arcones (2014):Ytot = cAGB x YAGB + cNSM x YNSM 12/15

Source(s) of #10464’s patterns• Neither standard s-process, nor i-process, nor SNe II or NSM
r-process patterns can fully reproduce the pattern of thisstar – either 1st or 2nd peaks can fit, but not simultaneously.
• In particular, the high Rb (and Sr) remain problematic.

• Isochrone fits: < 200 Myr old.
Contradiction to its positionon the horizontal branch(à ~12 Gyr).

100 Myr / 12 Gyr

0.5
11.5log g• Thinking aloud:87Rb could be produced, buthasn’t decayed (to 87Sr), yetà Sr is also highà requires that the star isyoung.

022.5
3
3.5
44.5
7500

7000

6500

6000

5500

5000

4500

Teff [K]Halo stars (Roederer et al. 2014)

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The first bulge NEMP star
• Further challenge: [N/Fe] = 0.95 à [C/N] ~ -0.5
• NEMP star and heavily affected by internal mixing(Spite et al. 2005; C.J. Hansen et al. 2016)• Presently observed photospheric abundances may not be
representative of the actual nucleosynthetic processes.
• It is imperative to also look at light elements (CNO…) toascertain that your stars are not self polluted!
• Most likely mixture of several events and nucleosynthetic
sites. Internal processes unlikely to enhance (Rb…) to theobserved levels.
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Summary• We detected “metal-poor” stars towards the bulge,
down to -2.7 dex, but most of them are halo-like.
• First CEMP(-s) and NEMP-stars in that population.
• What enriched star #10464? Neither s-process alone, nor iprocess, nor standard SNe II or NSM n-capture yields. 1stand 2nd peaks can never be simultaneously fit.
• It is likely that it was enriched by multiple events / sites.

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