(Proposal ID) S10A-043

(PI) Honda, Satoshi

(Proposal Title)
Enrichment of heavy elements in the Sextans dwarf Spheroidal Galaxy

(Abstract)
The astrophysical site of the r-process is still not well understood and is one
 of the hottest topic in nuclear astrophysics. Previous studies of Galactic 
halo stars have revealed that the r-process enrichment rapidly emerged at 
[Fe/H]~ -3,which can be an important constraint on identifying the 
astrophysical site of the r-process. We propose to examine this phenomenon for 
a satellite dwarf galaxy that has very different star formation history from 
the Galactic halo. Our recent study of extremely metal-poor stars in the 
Sextans dwarf galaxy found that the heavy element Ba of this galaxy's stars 
shows a large abundance scatter at [Fe/H]= -3 just as found for the Galactic 
halo. However, the data quality of our previous observations is insufficient 
for determining abundances of heavy elements other than Ba. We purpose to 
obtain high resolution spectra of two Ba-enhanced stars in this galaxy covering
 important heavy elements, in particular Eu, to estimate the fractions of the 
r-process and s-process contributions to heavy elements. If the origin of heavy
 elements is confirmed to be the r-process, that implies that the r-process 
appears from the metallicity of [Fe/H]= -3, independently of the enrichment 
history of galaxies, giving a new observational constraint on identifying the 
r-process site.