The Cassiopeia A Supernova Was of Type IIb
Oliver Krause,1*
Stephan M. Birkmann,1
Tomonori Usuda,2
Takashi Hattori,2
Miwa Goto,1
George H. Rieke,3
Karl A. Misselt3
Cassiopeia A is the youngest supernova remnant known in the
Milky Way and a unique laboratory for supernova physics. We
present an optical spectrum of the Cassiopeia A supernova near
maximum brightness, obtained from observations of a scattered
light echo more than three centuries after the direct light
of the explosion swept past Earth. The spectrum shows that Cassiopeia
A was a type IIb supernova and originated from the collapse
of the helium core of a red supergiant that had lost most of
its hydrogen envelope before exploding. Our finding concludes
a long-standing debate on the Cassiopeia A progenitor and provides
new insight into supernova physics by linking the properties
of the explosion to the wealth of knowledge about its remnant.
2 National Astronomical Observatory of Japan, 650 North A'ohoku Place, Hilo, HI 96720, USA.
3 Steward Observatory, 933 North Cherry Avenue, Tucson, AZ 85721, USA.
* To whom correspondence should be addressed. E-mail: krause{at}mpia.de
