(Proposal ID) S16B-064

(PI) Ishigaki, Miho

(Proposal Title)
K abundances in extremely metal-poor stars as a tracer of SN mechanisms

(Abstract)
The mechanism of core-collapse supernovae is still unclear. The most important 
factor for the explosions is the strength of the neutrino heating. The proton-
to-nucleon ratio (Y_e) in the inner most layer of the ejecta is a suitable 
probe to measure the strength of the neutrino heating. Since production of 
potassium (K) is known to be particularly sensitive to Y_e, K abundances in 
extremely metal-poor stars provide us with a powerful diagnostic to examine 
the Y_e, for which direct observation is not possible. We propose high-
resolution, high-signal-to-noise HDS spectroscopy of ~20 extremely metal-poor 
([Fe/H]<-3.5) stars, including newly discovered objects in recent literature, 
to obtain their potassium (K) abundances. The wavelength range including K I 
7665/7699 Angstrom resonance lines will be covered with spectral resolution 
R~60000. The proposed observation will provide us with the largest homogeneous 
data set of K abundances in the lowest metallicity stars. By comparing the 
derived K and other elemental abundances with the theoretical SN yields enable 
us to examine the possible values of Y_e, which is a critical test to yet 
unclear mechanisms of supernova explosions.