Mapping the r-process using
stellar observa4ons
Camilla Juul Hansen
Dark Cosmology Centre,
University of Copenhagen

OutlookCool, low-mass stars are the only astrophysicalobjects in which we can conduct a detailed andprecise abundance study of up to ∼70 elements•••••

Stellar abundances & parameters (observations of Mlow stars)
Old stars (RR Lyrae) – limitations in abundance patterns…
Tracing astrophysical formation sites using stellar abundances
Galactic Chemical Evolution
How many processes* are needed in the early Universe?
*or “contributions”

Camilla Juul HansenMultiple formation sites/mechan. may need to co-exist to explainàthe broad range of abundance patterns andà the abundance scatter seen at low metallicity• We need to explain the 3 dex abundance scatter around [Fe/H] = -3
• Deviations from solar r at the light end of the r-process (1st -2nd peak)
Camilla Juul Hansen

Low-mass, cool stars – why?

Low-mass (<1Mo) live long.
Stars with M < 0.7Mo are ~ 12
Gyr – typical for RR Lyr stars.
Camilla Juul Hansen

Observa4ons• High-resolu4on spectra• Broad wavelength rangeNaMg

Heavy elements
Camilla Juul Hansen

Stellar abundances

Camilla Juul Hansen

Camilla Juul Hansen

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Stellar parameters

Camilla Juul Hansen

Metallicity – impact on spectra[Fe/H] = log(NFe/NH)★ - log(NFe/NH)¤CJH et al. 2014b

Top: Solar ([Fe/H] = 0) spectrum – Mg triplet.
BoZom: Star with [Fe/H] ∼ -5. Christlieb +2004
Camilla Juul HansenAn observer’s periodic table

Camilla Juul Hansen

Record holding star - CS31082-001
Abundances of almost 70 elements,
37 of which are heavy elements.
Siqueira Mello et al. 2013

Tracing the yields from the ﬁrst stars?
•••••

RR lyr vs. Fe-poor stars – Two oldest, most MP RR Lyr (CJH + `11a)α-elements à SN Mass (Kobayashi + `06)
α/Zodd & Fe-peak àE51
Sc, Ti, Zn à Ye
In-/complete Si burn à Tpeak

Camilla Juul Hansen

CJH + 2011aTracing the yields from the ﬁrst stars?
• RR lyr vs. Fe-poor stars
Few absorp4onlines à few
abundances!
Molecularbands obscure.

Keller + `14 (1D, LTE): [Fe/H] < -7.1 – SN II: 60M¤Bessel + `15 (3D, NLTE – molec.): [Fe/H] < -7.5 – SNII: 40M¤
Nordlander + `17 (3D, NLTE – atom.): [Fe/H] < -6.5 –SNII Faint 10M¤ or ~2B 20-60M¤
Camilla Juul Hansen

Keller et al. 2014

Contribu4ons to single EMP stars
2 diﬀerent contribu4ons are needed!
Seen in star-to-star abundance scaZer + devia4on from solar r-paZern

Cowan + 2011
Camilla Juul Hansen

How many processes are needed at low [Fe/H]?
• Stellar paZerns: r-poor vs r-rich stars à diﬀerent
environments needed!
CJH et al. 2012

Observa4ons: Honda et al. 2004, 2007, Hill et al. 2002, Siqueira Melloet al. 2013; Yields: Wanajo et al. 2011
Camilla Juul Hansen

Constraining the physics…
• Stellar abundances vs yield predic4ons may help
constrain Ye

Observa4ons: CJH+2012, Yields: Wanajo et al. 2011
Camilla Juul Hansen

Solar System abundance – Solar-s=r…
CJH+12• Once we focus on r-poor stars,
diﬀerent processes like the weak r
can be detected.
• The r-poor stars do not agree
perfectly with Solar – s = r.
• Solar system abundances areintegrated over billions of years andare highly convolved – they may not
be the best r-tracers despite theirlarge number and accuracy!
Camilla Juul Hansen

Primary processes: Co-produc4on or not?

• Two elements produced in the same way, most likely
grow at the same rate over 4me if the process isrobust and show a small abundance scaZer.
• The lighter 38 < Z < 50 seem not always to be coproduced with the heavy elements (Z > 56)(Burris et al. 2000, Montes et al. 2007, Francois et al. 2007, CJH et al. 2012, 2014)
Camilla Juul Hansen

Mining for Silver• Sr ~ 85% s, Ba ~ 81%, Eu~94% r vs Ag 79% “r”?
(Arlandini et al 1999, Bisterzo et al. 2014)

CJH et al. 2012

Blue: Higher metallicity
dwarf stars [Fe/H] > -2.0

Ag not weak s/
charged par4cle ormain r-process!

Red: Lower metallicity giants
down to [Fe/H] ~ -3.5
Camilla Juul Hansen

Mining for Silver• Ru, Pd, and Ag co-produced at low metallicity

CJH et al. 2011, 2012

CJH et al. 2014

Ru – Ag: Weak r-process – higher Ye, closer to stability than main r– maybe a wind from SN or NSM
Camilla Juul Hansen

New rare earth element observa4ons• Tight correla4on à similar forma4on mechanism• Diﬀerence in origin à ScaZer!
Eu – Er are co-produced they require a low Ye à compact merger event (NSM)

CJH et al. 2017 in prep.

Camilla Juul Hansen

Contribu4ons to many stars (GCE)
2 diﬀerent contribu4ons are needed!
Seen in star-to-star abundance scaZer + devia4on from solar r-paZern

CJH + 2012
Camilla Juul Hansen

Galac4c Chemical Evolu4on (GCE)

Camilla Juul Hansen

GCE of Sr• Sr is one of the best heavy element tracers owing
to strong lines (CJH et al. 2013)• We can separate yield contribu4ons and assessstar-to-star abundance scaZer
log gNLTE - log gLTE

1.0

giantsdwarfs

0.8
0.6
0.4
0.2
0.0
-0.2
123
log gLTE

45[Fe/H]NLTE - [Fe/H]LTE

0.4

giantsdwarfs

0.3
0.2
0.1

CJH et al. 2013

0.0-0.1-5-4-3-2[Fe/H]LTE-10Camilla Juul Hansen

GCE of Sr• We can separate yield contribu4ons and assessstar-to-star abundance scaZer• NLTE corr. cannot explain scaZer à nuclear origin!
CJH et al. 2013

Yields from: Wanajo +`11,

Arcones & Montes `11,
Camilla Juul Hansen

Frischknecht +`12

Stellar abundances & forma4on processes
ScaZer à Mul4ple forma4on sites• Weak s (Z ≤ 40)• Main s (broad range, Ba, Z ≥ 50)• Weak r (~40 < Z < 50)• Main r (full range, or Z > 50)(CJH et al. 2014b)

Camilla Juul Hansen

Are 2 “processes” suﬃcient?
Assump4ons (EMP stars):• There are 2 robust processes: mainr (H), weak r (L) (e.g., Qian & Wasserburg2007)• M1: H=CS22892-052, L=HD122563• M2: H=CS22892-052, H+L = HD122563• M3: H+L=CS22892-052, H+L=HD122563 –all stars are mixed (Li et al. 2013)

Ycalc(Z) = (CHYH(Z) + CLYL(Z)) * 10[Fe/H]
Camilla Juul Hansen(CJH et al. 2014b)

ScaZer and robustness of processes(CJH et al. 2014b)

Camilla Juul HansenSN ν-winds as L/weak r forma4on site

(CJH et al. 2014b)

Summary• A broad variety of stars carry key informa4on on the nature of the r-process• When looking at stellar abundance paZerns and comparing to yields – weneed to know how our 1D, LTE assump4ons bias the paZern• A broad parameter range may be needed at the host site (NSM vs SN) toexplain Sr – Ag vs Eu – Er – or we have a mixture of both…
à NSM and SN (ν-driven winds) seem to co-exist and we need to explore
how these mix and what that does to the stellar abundance paZern…
• Age – [Fe/H] is not a perfect clock – intrinsically old r-normal stars also carry
key informa4on on the ﬁrst primary processes that produce r-processmaterial:
We seem to understand the 25 r-II stars – but what about the r-poor halostars (Honda-like stars)?
• If the r-process is robust and universal – it must be able to explain theabundance paZerns we see in both the Galac4c halo, disk, as well as UFD /dSph and Globular clusters. This is the challenge.
• Two primary processes/condi4ons seem to be needed to explain the r-poor
as well as the r-rich (rII) stars!
• New challenge: How does the NSM dynamic ejecta mix with the wind/disk?
Camilla Juul HansenFuture• Outlook – E-ELT & 4MOST

Camilla Juul Hansen

Thank You!

Camilla Juul Hansen