CHARGED-PARTICLE AND NEUTRON-CAPTURE PROCESSES IN THE HIGH-ENTROPY WIND OF CORE-COLLAPSE SUPERNOVAE

By K. Farouqi, K. Kratz, B. Pfeiffer, T. Rauscher, F. Thielemann, J. Truran, T. Ch, Ch. 2010

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The astrophysical site of the r-process is still uncertain, and a full exploration of the systematics of this process in terms of its dependence on nuclear properties from stability to the neutron drip-line within realistic stellar environments has still to be undertaken. Sufficiently high neutron-to-seed ratios can only be obtained either in very neutron-rich low-entropy environments or moderately neutron-rich high-entropy environments, related to neutron star mergers (or jets of neutron star matter) and the high-entropy wind of core-collapse supernova explosions. As chemical evolution models seem to disfavor neutron star mergers, we focus here on high-entropy environments characterized by entropy S, electron abundance Ye, and expansion velocity Vexp. We investigate the termination point of charged-particle reactions, and we define a maximum entropy Sfinal for a given Vexp and Ye, beyond which the seed production of heavy elements fails due to the very small matter density. We then investigate whether an r-process subsequent to the charged-particle freeze-out can in principle be understood on the basis of the classical approach, which assumes a chemical equilibrium between neutron captures and photodisintegrations, possibly followed by a β-flow equilibrium. In particular, we illustrate how long such a chemical equilibrium approximation holds, how the freeze-out from such conditions affects the abundance pattern, and which role the late capture of neutrons originating from β-delayed neutron emission can play. Furthermore, we analyze the impact of nuclear properties from different theoretical mass models on the final abundances after these late freeze-out phases and β-decays back to stability. As only a superposition of astrophysical conditions can provide a good fit to the solar r-abundances, the question remains how such superpositions are attained, resulting in the apparently robust r-process pattern observed in low metallicity stars.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/dd2433f28a53bcb98b7014b515494e5dcde9b063

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Citations in the corpus

MAGNETOROTATIONALLY DRIVEN SUPERNOVAE AS THE ORIGIN OF EARLY GALAXY r-PROCESS ELEMENTS? (2012, background): “The initially postulated neutrino wind in regular (neutrino-driven) supernovae (Hoffman et al. 1997; Meyer & Brown 1997; Farouqi et al. 2010) (a) did not result in having sufficiently high entropies (Thompson et al. 2001; Wanajo 2006; Arcones et al. 2007), and (b) in addition, the innermost ejecta…”
The s-Process in Low Metallicity Stars. II. Interpretation of High-Resolution Spectroscopic Observations with AGB models (2011, background): “From the theoretical point of view, several models have been advanced (Farouqi et al. 2010; Qian & Wasserburg 2008, 2007; Kratz et al. 2007; Wanajo & Ishimaru 2006), but an exhaustive interpretation is still lacking.”
Near-Field Cosmology with Extremely Metal-Poor Stars (2015, background): “These upper limits indicate no more than one production event (or even none) in which these heavy elements may have formed (Farouqi et al. 2010).”
The s process: Nuclear physics, stellar models, and observations (2010, background): “There is general consensus for the need of an additional LEPP source of yet unknown origin for the light isotopes, including Sr, Y, and Zr, an issue that is still highly debated (Farouqi et al., 2010; Pignatari et al., 2010; Qian and Wasserburg, 2007).”
On the astrophysical robustness of the neutron star merger r-process (2012, background): “Despite the long history of ns2 simulations we 3 At higher temperatures the radiation pressure must necessarily include contribution from electron-positron pairs (Witti et al. 1994; Farouqi et al. 2010). are not aware of any study that has systematically explored such a wide range of ns masses.”
NUGRID STELLAR DATA SET. I. STELLAR YIELDS FROM H TO BI FOR STARS WITH METALLICITIES Z = 0.02 and Z = 0.01 (2013, background): “…scenarios are the neutrinoinduced winds from the CCSNe, before the formation of the reverse shock (e.g., Woosley et al. 1994; Wanajo et al. 2001; Farouqi et al. 2010) or after the fallback started (e.g., Fryer et al. 2006; Arcones et al. 2007); the polar jets from rotating…”