Constraining Collapsar r-Process Models through Stellar Abundances. (arXiv:1905.04315v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Macias_P/0/1/0/all/0/1">Phillip Macias</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ramirez_Ruiz_E/0/1/0/all/0/1">Enrico Ramirez-Ruiz</a>
We use observations of heavy elements in very metal-poor stars ([Fe/H] <
-2.5) in order to place constraints on the viability of collapsar models as a
significant source of the r-process. We combine bipolar explosion
nucleosynthesis calculations with recent disk calculations to make predictions
of the observational imprints these explosions would leave on very metal-poor
stars. We find that a source of low (~ 0.1-0.5 $M_odot$) Fe mass which also
yields a relatively high (> 0.08 $M_odot$) r-process mass would, after
subsequently mixing and forming new stars, result in [r/Fe] abundances up to
three orders of magnitude higher than those seen in stars. In order to match
inferred abundances, 10-10$^3 M_odot$ of Fe would need be efficiently
incorporated into the r-process ejecta. We show that Fe enhancement and hence
[r/Fe] dilution from other nearby supernovae is not able to explain the
observations unless significant inflow of pristine gas occurs before the ejecta
are able to form new stars. Finally, we show that the inferred [Eu/Fe]
abundances require levels of gas mixing which are in conflict with other
properties of r-process enhanced metal-poor stars. Our results suggest that
early r-process production is likely to be spatially uncorrelated with Fe
production, a condition which can be satisfied by neutron star mergers due to
their large kick velocities and purely r-process yields.
We use observations of heavy elements in very metal-poor stars ([Fe/H] <
-2.5) in order to place constraints on the viability of collapsar models as a
significant source of the r-process. We combine bipolar explosion
nucleosynthesis calculations with recent disk calculations to make predictions
of the observational imprints these explosions would leave on very metal-poor
stars. We find that a source of low (~ 0.1-0.5 $M_odot$) Fe mass which also
yields a relatively high (> 0.08 $M_odot$) r-process mass would, after
subsequently mixing and forming new stars, result in [r/Fe] abundances up to
three orders of magnitude higher than those seen in stars. In order to match
inferred abundances, 10-10$^3 M_odot$ of Fe would need be efficiently
incorporated into the r-process ejecta. We show that Fe enhancement and hence
[r/Fe] dilution from other nearby supernovae is not able to explain the
observations unless significant inflow of pristine gas occurs before the ejecta
are able to form new stars. Finally, we show that the inferred [Eu/Fe]
abundances require levels of gas mixing which are in conflict with other
properties of r-process enhanced metal-poor stars. Our results suggest that
early r-process production is likely to be spatially uncorrelated with Fe
production, a condition which can be satisfied by neutron star mergers due to
their large kick velocities and purely r-process yields.
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