Volume 494, Number 3, February II 2009
|Page(s)||829 - 844|
|Published online||22 December 2008|
On the dynamics of proto-neutron star winds and r-process nucleosynthesis
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85748 Garching, Germany
2 Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya 25, Moscow 117218, Russia e-mail: Igor.Panov@itep.ru
Accepted: 26 November 2008
We study here the formation of heavy r-process nuclei in the high-entropy environment of rapidly expanding neutrino-driven winds from compact objects. In particular, we explore the sensitivity of the element creation in the region to the low-temperature behavior of the outflows. For this purpose we employ a simplified model of the dynamics and of the thermodynamical evolution for radiation dominated, adiabatic outflows. It consists of a first stage of fast, exponential cooling with timescale , followed by a second phase of slower evolution, assuming either constant density and temperature or a power-law decay of these quantities. These cases describe a strong deceleration or decreasing acceleration of the transsonic outflows, respectively, and thus are supposed to capture the most relevant effects associated with a change in the wind expansion behavior at large radii, for example because of the collision with the slower, preceding supernova ejecta and the possible presence of a wind termination shock. We find that for given entropy, expansion timescale, and proton-to-baryon ratio not only the transition temperature between the two expansion phases can make a big difference in the formation of the platinum peak, but also the detailed cooling law during the later phase. Because the nuclear photodisintegration rates between about K and roughly 109 K are more sensitive to the temperature than the neutron-capture rates are to the free neutron density, a faster cooling but continuing high neutron density in this temperature regime allow the r-process path to move closer to the neutron-drip line. With low (γ,n)- but high β-decay rates, the r-processing does then not proceed through a (γ, n)-(n, γ) equilibrium but through a quasi-equilibrium of (n, γ)-reactions and β-decays, as recently also pointed out by Wanajo. Unless the transition temperature and corresponding (free neutron) density become too low ( K), a lower temperature or faster temperature decline during the slow, late evolution phase therefore allow for a stronger appearance of the third abundance peak.
Key words: nuclear reactions, nucleosynthesis, abundances / stars: supernovae: general / stars: winds, outflows / stars: neutron
© ESO, 2009
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.