[32.02] Hypernovae and Their Nucleosynthesis

AAS 200th meeting, Albuquerque, NM, June 2002
Session 32. Core-Collapse of Massive Stars: Supernovae and Gamma-Ray Bursts
Topical Session Oral, Tuesday, June 4, 2002, 8:30-10:00am, 10:45am-12:30pm, 2:00-3:30pm, 3:45-5:30pm, Ballroom C

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[32.02] Hypernovae and Their Nucleosynthesis

K. Nomoto (U. Tokyo)

We review the characteristics of nucleosynthesis in 'Hypernovae', i.e., supernovae with very large explosion energies ( \gtrsim 10⁵² ergs). The hypernova yields compared to those of ordinary core-collapse supernovae show the following characteristics: 1) Complete Si-burning takes place in more extended region, so that the mass ratio between the complete and incomplete Si burning regions is generally larger in hypernovae than normal supernovae. As a result, higher energy explosions tend to produce larger [(Zn, Co)/Fe], small [(Mn, Cr)/Fe], and larger [Fe/O], which could explain the trend observed in very metal-poor stars. 2) Si-burning takes place in lower density regions, so that the effects of \alpha-rich freezeout is enhanced. Thus ⁴⁴Ca, ⁴⁸Ti, and ⁶⁴Zn are produced more abundantly than in normal supernovae. The large [(Ti, Zn)/Fe] ratios observed in very metal poor stars strongly suggest a significant contribution of hypernovae. 3) Oxygen burning also takes place in more extended regions for the larger explosion energy. Then a larger amount of Si, S, Ar, and Ca (``Si") are synthesized, which makes the ``Si"/O ratio larger. The abundance pattern of the starburst galaxy M82 may be attributed to hypernova explosions. Asphericity in the explosions strengthens the nucleosynthesis properties of hypernovae except for ``Si"/O. We thus suggest that hypernovae make important contribution to the early Galactic (and cosmic) chemical evolution.

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