PUSHing Core-Collapse Supernovae to Explosions in Spherical Symmetry: Nucleosynthesis Yields

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by  Sanjana Sinha

PUSHing Core-Collapse Supernovae to Explosions in
Spherical Symmetry: Nucleosynthesis Yields
SanjanaSinha1,CarlaFro¨hlich1,KevinEbinger2,AlbinoPerego3,MatthiasHempel2,
7 MariusEichler2,3,MatthiasLiebendo¨rfer2,andFriedrich-Karl Thielemann2
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0 1DepartmentofPhysics,NorthCarolinaStateUniversity,Raleigh,NC,29695-8202,USA
2 2Departmentfu¨rPhysik,Universita¨tBasel,CH-4056Basel,Switzerland
3Institutfu¨rKernphysik,TechnischeUniversita¨tDarmstadt,D-64289Darmstadt,Germany
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a E-mail:[email protected]
J

8 (ReceivedAug20,2016)
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Core-collapsesupernovae(CCSNe)aretheextremelyenergeticdeathsofmassivestars.Theyplaya

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R vital role in the synthesis and dissemination of many heavy elements in the universe. In the past,
CCSN nucleosynthesis calculations have relied on artificial explosion methods that do not ade-
S
quatelycapturethephysicsoftheinnermostlayersofthestar.ThePUSHmethod,calibratedagainst
.
h
SN1987A,utilizestheenergyofheavy-flavorneutrinosemittedby theproto-neutronstar (PNS) to
p
triggerparametrizedexplosions.ThismakesitpossibletofollowtheconsistentevolutionofthePNS
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o andtoensurea moreaccuratetreatmentofthe electronfractionoftheejecta.Here,wepresentthe
r Irongroupnucleosynthesisresultsforcore-collapsesupernovae,explodedwithPUSH,fortwodiffer-
t
s entprogenitorseries.Comparisonsofthecalculatedyieldstoobservationalmetal-poorstardataare
a
[ alsopresented.Nucleosynthesisyieldswillbecalculatedforallelementsandoverawiderangeof

progenitormasses.Theseyieldscanbeimmenselyusefulformodelsofgalacticchemicalevolution.
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v KEYWORDS: stars:supernovae:general,nucleosynthesis
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0 1. Introduction
.
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0 The detailed mechanism of core-collapse supernovae is still an open question which is being
7 investigated usingsophisticated multi-dimensional models.However,atthepresenttime,thesemod-
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elsaretoocomputationally expensiveforsystematicnucleosynthesis studiesofmultipleprogenitors.
:
v For a recent review of multi-dimensional core-collapse simulations, see Janka et al. (2016) [1] and
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X references therein. Inordertomakenucleosynthesis predictions anddiscover generaltrends, westill
r requirerobustandreadilycalculable modelswhichcapturetherelevantphysicsoftheexplosion.
a
The PUSH method [2] triggers explosions in otherwise non-exploding simulations by paramet-
rically increasing the efficiency of neutrino energy deposition inside the gain region. This is done
bydepositing afraction oftheluminosity ofheavy-flavor neutrinos (emitted bythePNS)behind the
shock. The mass cut emerges naturally in the simulation and the electron fraction is followed con-
sistently. Despite their effective character, PUSHmodels are robust, computationally affordable and
self-consistent. We present the Iron group nucleosynthesis yields for CCSNe,calculated for models
fromtwoprogenitor series,exploded usingPUSH.
2. Methods
The evolution of the electron fraction (Y ) strongly affects nucleosynthesis in the innermost
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ejected stellar layers, where the predominant production of Iron group elements occurs. The Y can
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changeduetoelectron neutrinoandanti-neutrino interactions.
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PUSH simulations follow the Y evolution consistently and provide input trajectories for post-
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processing, asoutlined in [2]. Theisotropic diffusion source approximation (IDSA)[3]is employed
forelectronneutrinoandanti-neutrinotransportwhileanadvancedspectralleakage(ASL)[4]scheme
isusedfortransportofheavy-lepton flavorneutrinos. Thenuclearreactionnetwork,CFNET,follows
theabundances of∼2000isotopestocomputethecompositionofthesupernovaejecta.Theisotopes
includedcovertheneutron-deficient aswellastheneutron-rich sideofthevalleyofβ-stability.
3. Results
Sneden etal.(2016) [5]used themostrecent and improved laboratory datafor Fe-group neutral
and singly-ionized transitions to derive robust abundances in the very metal-poor main sequence
turnoff star HD 84937. Figure 1 shows the reported abundance ratios of Fe-group elements along
with the PUSH nucleosynthesis yields for the Fe-group. The yields depicted are for solar and sub-
solar metallicity progenitors from Woosley et al. (2002) [6](WHW02). Different combinations of
parameters t and k correspond to variations in the artificial heating provided by PUSH, selected
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to satisfy observational constraints from SN1987A. There are no significant variations seen in the
[X/Fe]valuesobtained forthedifferentparametersettings.
PUSH yields are shown in Figure 2 along with piston yields from Woosley et al. (1995) [7]
and thermal bomb yields from Thielemann et al. (1996) [8] for a 25M⊙ model from the WHW02
progenitor set. For most members of this progenitor set, Manganese ratios are found to be very low
comparedtothoseseeninHD84937.
PUSHyieldswerecalculatedfortheWoosleyetal.(2007)[9](WH07)progenitor seriesinaddi-
tiontoWHW02progenitors. Most oftheFe-group yields forWH07progenitors aresimilar tothose
for WHW02 progenitors but Manganese ratios show a marked improvement. Figure 3 shows the
calculated yieldsfora25M⊙ WH07progenitor.
4. Conclusions andOutlook
We find that explosions with detailed Y evolution give a much better match with observational
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abundancesinHD84937.Additionally,theFe-groupnucleosynthesis yieldsappeartodependsignif-
icantlyonthechoiceofprogenitor series.
Nucleosynthesis yields will be calculated for all elements and over a wide range of progenitor
massesinafuturework[10],available asinputformodelsofgalacticchemicalevolution.
Acknowledgments
This work is supported through an Early Career Award by the United States Department of En-
ergy(DOEgrantno.SC0010263).
References
[1] H.-T.Janka,T.MelsonandA.Summa:Ann.Rev.Nucl.Part.Sci.,66(2016)341
[2] A.Perego,M.Hempel,C.Fro¨hlichetal.:ApJ,806(2015)275
[3] M.Liebendo¨rfer,S.C.WhitehouseandT.Fischer:ApJ,698(2009)1174
[4] A.Perego,R.M.Cabezo´nandR.Ka¨ppeli:ApJSuppl.,223(2016)22
[5] C.Sneden,J.J.CowanandC.Kobayashi:ApJ,817(2016)53
[6] S.E.Woosley,A.HegerandT.A.Weaver:Rev.Mod.Phys.,74(2002)1015
[7] S.E.WoosleyandT.A.Weaver:ApJS,101(1995)181
[8] F.-K.Thielemann,K.NomotoandM.-A.Hashimoto:ApJ,460(1996)408
[9] S.E.WoosleyandA.Heger:Phys.Rep.,442(2007)269
[10] S.Sinhaetal.:inpreparation
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Fig. 1. Observed abundances of HD 84937 compared with the yields for solar (left panel) and sub-solar
(rightpanel)metallicity24M⊙WHW02progenitors.
Fig. 2. Yieldsforthesolarmetallicity25M⊙WHW02progenitoralongwithpiston(leftpanel)andthermal
bomb(rightpanel)yields.
Fig. 3. Yields for the solar metallicity 25M⊙ WH07 progenitoralong with piston (left panel) and thermal
bomb(rightpanel)yields.
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