(Proposal ID) S12B-021

(PI) Kawabata, Koji

(Proposal Title)
Late-time spectroscopy of envelope-stripped SNe: Figuring the central engine

(Abstract)
We propose to perform late-time spectroscopy of envelope-stripped core-
collapse supernovae (SNe), i.e., Type Ib/c/IIb SNe. We aim to examine the 
explosion physics and its dependence on the progenitor mass. The key 
information is the asphericity and the chemical composition of the inner 
atmosphere, which can be explored by late-time observations. The difference 
in [O I] line profiles indicates that GRB-associated energetic SNe Ic (like 
SN 1998bw) and non-GRB energetic SNe Ic (2003jd) are intrinsically similar 
aspherical explosions that are differently viewed (pole-on for 1998bw and 
nearly edge-on for 2003jd). Our continuing study suggests that the asphericity 
is rather common characteristic even for normal energy SNe without a GRB. 
However, it is still unclear how the intermediate types of SNe (SNe Ib/IIb) 
are produced and how they connected with other types of core-collapse SNe. 
High-quality late-time spectra of SNe Ib/Ic/IIb are still lacking. We propose 
to obtain a larger number of nebular spectra of envelope-stripped SNe 
including SNe IIb so that we examine the degree of the asphericity explosion 
energy, amount of synthesized ^56Ni and the physical properties of the central 
remnant as a function of the progenitor's mass.