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Title: OPACITIES AND SPECTRA OF THE r-PROCESS EJECTA FROM NEUTRON STAR MERGERS

Material ejected during (or immediately following) the merger of two neutron stars may assemble into heavy elements through the r-process. The subsequent radioactive decay of the nuclei can power transient electromagnetic emission similar to, but significantly dimmer than, an ordinary supernova. Identifying such events is an important goal of future optical surveys, offering new perspectives on the origin of r-process nuclei and the astrophysical sources of gravitational waves. Predictions of the transient light curves and spectra, however, have suffered from the uncertain optical properties of heavy ions. Here we argue that the opacity of an expanding r-process material is dominated by bound-bound transitions from those ions with the most complex valence electron structure, namely the lanthanides. For a few representative ions, we run atomic structure models to calculate the radiative transition rates for tens of millions of lines. The resulting r-process opacities are orders of magnitude larger than that of ordinary (e.g., iron-rich) supernova ejecta. Radiative transport calculations using these new opacities suggest that the light curves should be longer, dimmer, and redder than previously thought. The spectra appear to be pseudo-blackbody, with broad absorption features, and peak in the infrared ({approx}1 {mu}m). We discuss uncertainties in the opacities andmore » attempt to quantify their impact on the spectral predictions. The results have important implications for observational strategies to find and study the radioactively powered electromagnetic counterparts to neutron star mergers.« less
Authors:
;  [1] ;  [2]
  1. Department of Physics and Astronomy, University of California, Berkeley, CA 94720 (United States)
  2. Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom)
Publication Date:
OSTI Identifier:
22133983
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 774; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ELECTRONIC STRUCTURE; FIELD EMISSION; GRAVITATIONAL WAVES; HEAVY IONS; IRON; NEUTRON STARS; NUCLEAR DECAY; OPACITY; R PROCESS; RADIANT HEAT TRANSFER; RARE EARTHS; SPECTRA; VALENCE; VISIBLE RADIATION