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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)
Terese T. Hansen 9/9