R-Process Alliance:Observations of Stellar Abundances

Terese T. Hansen

JINA Horizons

Dec 1, 2020

Terese T. Hansen 1/9

Nuclear Astrophysics with Stellar Abundances

Nucleosynthesis event

Enriching interstellar medium

Low mass star we can observe today

Measure number of Eu

atoms present in star

produced in the nucleosynthesis

event.

Terese T. Hansen 2/9

R-Process Alliance

Core members: Tim Beers (University of Notre Dame), AnnaFrebel (Massachusetts Institute of Technology), Vini Placco

(NOIRLab), Ian Roederer (University of Michigan), Charli Sakari(San Francisco State University), Rana Ezzeddine (University of

Florida), Erika Holmbeck (Rochester Institute of Technology), andTerese Hansen (Texas A&M University).

Terese T. Hansen 3/9

RPA Target Selection

Bright, V < 13.5 → can observe many stars in short timeCold, 4000 < Teff < 5500 → Get Eu abundance or goodupper limitsMetal poor, [Fe/H] < −2 → Only few nucleosynthesis events

3600 4000 4400 4800 5200 5600

CaII K CaII H + H�

CH G-band

H�

H�

H�

MgIMgI

MgI

RAVE J2038-0023KPNO/MayallRCSPEC

Teff = 4692 Klog(g) = 0.73[Fe/H] = -3.18[C/Fe] = +0.17[�/Fe] = +0.22

S/N (4000�) = 66

V = 12.7J = 10.7

(B-V) = 0.98(J-K) = 0.66

� (�)

3900 4000 4100 4200� (�)

templateobserved (smoothed)

4200 4300 4400 4500� (�)

templateobserved (smoothed)

5000 5100 5200 5300� (�)

templateobserved (smoothed)

Placco+ 2018

Terese T. Hansen 4/9

RPA - Snapshots

R ∼ 25000, S/N∼ 30

Terese T. Hansen 5/9

RPA - DR4r-II: [Eu/Fe] > 0.7, [Ba/Eu] < 0r-I: 0.3 < [Eu/Fe] < 0.7, [Ba/Eu] < 0limited-r: [Sr/Ba] > 0.5, [Eu/Fe] < 0.3

Holmbeck+ 2020

Terese T. Hansen 6/9

RPA Abundances for R-II Star

-1.0

0.0

1.0

2.0

3.0lo

gε

HD 222925Solar r-processSolar r-process (scaled to Eu)Solar s-process (scaled to Ba)

RbSr

YZr

NbMoRu

RhPd

AgBa

LaCe

PrNdSm

EuGd

TbDy

HoErTm

YbLu

Hf OsIr

Pb Th U

30 40 50 60 70 80 90Atomic Number, Z

-1.0

0.0

1.0

∆lo

gε

Roederer+ 2018

Terese T. Hansen 7/9

Scatter in Stellar ParametersCS 22892-052

Teff Logg Vturb [Fe/H] [Eu/Fe] log �(Eu) err R / SNR Ref4790 1.60 1.80 -2.91 1.53 -0.86 0.02 90,000/60 Honda 20044884 1.81 1.67 -2.95 1.53 -0.90 0.23 20,000/46 Barklem 20054884 1.81 1.67 -2.78 1.36 -0.90 20,000/50 Ren 20124710 1.50 2.10 -3.20 1.75 -0.93 0.09 60,000/150 Sneden 20004800 1.50 1.95 -3.10 1.63 -0.95 0.03 60,000/100 Sneden 20034850 1.60 1.90 -3.03 1.48 -1.03 47,000/130 Francois 20074690 1.15 1.50 -3.24 1.44 -1.28 0.22 41,000/270 Roederer 2014

CS 31082-001Teff Logg Vturb [Fe/H] [Eu/Fe] log �(Eu) err R / SNR Ref

4790 1.80 1.90 -2.80 1.69 -0.59 0.01 50,000/100 Honda 20044922 1.90 1.88 -2.78 1.65 -0.61 0.22 20,000/90 Barklem 20054922 1.90 1.88 -2.61 1.48 -0.61 20,000/50 Ren 20124925 1.51 1.40 -2.81 1.53 -0.76 0.31 40,000/100 Hansen 20124825 1.50 1.80 -2.90 1.62 -0.76 0.11 86,000/300 Hill 20024650 1.05 1.55 -3.09 1.44 -1.13 0.16 41,000/150 Roederer 2014

Terese T. Hansen 8/9

Accomplishments and Future Directions

DataRPA - abundances for >100 highly r-process enhanced starsusing NLTE stellar parametersOther large surveys providing neutron-capture elementabundances GALAH, 4MOST, WEAVEStellar kinematics from Gaia survey

ModelingUsing stellar abundances to characterize nucleosynthesis sitesand event rates (Holmbeck+ 2020b, Brauer+ 2020, Ji+ 2019,others)NLTE abundance corrections for a number of key r-processelements (including Nd, Ag and others).

Wish ListContinued access to high-resolution UV spectroscopy (HSTnow; potentially CETUS, Haber, or BEAUVOIR in the future)

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