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Tycho Brahe’s 1572 supernova as a standard type Ia as revealed by its light-echo spectrum


Type Ia supernovae are thermonuclear explosions of white dwarf stars in close binary systems1. They play an important role as cosmological distance indicators and have led to the discovery of the accelerated expansion of the Universe2,3. Among the most important unsolved questions4 about supernovae are how the explosion actually proceeds and whether accretion occurs from a companion or by the merging of two white dwarfs. Tycho Brahe’s supernova of 1572 (SN 1572) is thought to be one of the best candidates for a type Ia supernova in the Milky Way5. The proximity of the SN 1572 remnant has allowed detailed studies, such as the possible identification of the binary companion6, and provides a unique opportunity to test theories of the explosion mechanism and the nature of the progenitor. The determination of the hitherto unknown7,8,9 spectroscopic type of this supernova is crucial in relating these results to the diverse population of type Ia supernovae10. Here we report an optical spectrum of Tycho’s supernova near maximum brightness, obtained from a scattered-light echo more than four centuries after the direct light from the explosion swept past the Earth. We find that SN 1572 belongs to the majority class of normal type Ia supernovae.

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Figure 1: Optical images of the SN 1572 light echo.
Figure 2: Spectrum of SN 1572 and comparison spectra of normal type Ia supernovae.
Figure 3: Comparison of SN 1572 with type Ia supernovae of different luminosities.


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This work is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, and the German–Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía. We thank U. Thiele and the Calar Alto observers for their support. M.T. is supported by the Japan Society for the Promotion of Science Research Fellowship for Young Scientists. This research has been supported in part by the World Premier International Research Center Initiative, MEXT, Japan.

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Correspondence to Oliver Krause or Ken’ichi Nomoto.

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Krause, O., Tanaka, M., Usuda, T. et al. Tycho Brahe’s 1572 supernova as a standard type Ia as revealed by its light-echo spectrum. Nature 456, 617–619 (2008).

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