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Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers

Lippuner, Jonas and Fernández, Rodrigo and Roberts, Luke F. and Foucart, Francois and Kasen, Daniel and Metzger, Brian D. and Ott, Christian D. (2017) Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers. Monthly Notices of the Royal Astronomical Society, 472 (1). pp. 904-918. ISSN 0035-8711.

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We investigate the nucleosynthesis of heavy elements in the winds ejected by accretion discs formed in neutron star mergers. We compute the element formation in disc outflows from hypermassive neutron star (HMNS) remnants of variable lifetime, including the effect of angular momentum transport in the disc evolution. We employ long-term axisymmetric hydrodynamic disc simulations to model the ejecta, and compute r-process nucleosynthesis with tracer particles using a nuclear reaction network containing ∼8000 species. We find that the previously known strong correlation between HMNS lifetime, ejected mass and average electron fraction in the outflow is directly related to the amount of neutrino irradiation on the disc, which dominates mass ejection at early times in the form of a neutrino-driven wind. Production of lanthanides and actinides saturates at short HMNS lifetimes (≲10 ms), with additional ejecta contributing to a blue optical kilonova component for longer-lived HMNSs. We find good agreement between the abundances from the disc outflow alone and the solar r-process distribution only for short HMNS lifetimes (≲10 ms). For longer lifetimes, the rare-earth and third r-process peaks are significantly underproduced compared to the solar pattern, requiring additional contributions from the dynamical ejecta. The nucleosynthesis signature from a spinning black hole (BH) can only overlap with that from an HMNS of moderate lifetime (≲60 ms). Finally, we show that angular momentum transport not only contributes with a late-time outflow component, but that it also enhances the neutrino-driven component by moving material to shallower regions of the gravitational potential, in addition to providing additional heating.

Item Type:Article
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URLURL TypeDescription Paper
Lippuner, Jonas0000-0002-5936-3485
Roberts, Luke F.0000-0001-7364-7946
Ott, Christian D.0000-0003-4993-2055
Additional Information:© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 August 1; Received 2017 July 13; in original form 2017 March 17; Published: 09 August 2017. JL and CDO acknowledge support from U.S. National Science Foundation (NSF) grant AST-1333520. RF acknowledges support from the University of California Office of the President, from NSF grant AST-1206097, and from the Faculty of Science at the University of Alberta. DK is supported in part by a U.S. Department of Energy (DOE) Office of Nuclear Physics Early Career Award, and by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Divisions of Nuclear Physics, of the DOE under Contract No. DE-AC02-05CH11231. The software used in this work was in part developed by the Flash Center at the University of Chicago funded by the DEO Office of Advanced Scientific Computing Research (OASCR) and the Advanced Simulation and Computing (ASC) program of the DOE's National Nuclear Security Administration (NNSA). This research used resources of the National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Some computations were performed on the Edison compute cluster (repository m2058). Some of the calculations were performed on the Zwicky compute cluster at Caltech, supported by NSF under the Major Research Instrumentation (MRI) award PHY-0960291 and by the Sherman Fairchild Foundation. This work was supported in part by NSF grant PHY-1430152 (JINA Center for the Evolution of the Elements). CDO thanks the Yukawa Institute for Theoretical Physics for support and hospitality. This article has been assigned Yukawa Institute report number YITP-17-26.
Group:TAPIR, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
University of California, BerkeleyUNSPECIFIED
University of AlbertaUNSPECIFIED
Department of Energy (DOE)DE-AC02-05CH11231
Sherman Fairchild FoundationUNSPECIFIED
Subject Keywords:accretion, accretion discs – dense matter – gravitational waves – hydrodynamics – neutrinos – nuclear reactions, nucleosynthesis, abundances
Record Number:CaltechAUTHORS:20171117-125429012
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Official Citation:Jonas Lippuner, Rodrigo Fernández, Luke F. Roberts, Francois Foucart, Daniel Kasen, Brian D. Metzger, Christian D. Ott; Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers, Monthly Notices of the Royal Astronomical Society, Volume 472, Issue 1, 21 November 2017, Pages 904–918,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83292
Deposited By: Tony Diaz
Deposited On:20 Nov 2017 19:49
Last Modified:20 Nov 2017 19:49

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