Deviations from axisymmetry revealed by line polarization in the normal type Ia supernova 2004S

Ryan Chornock*, Alexei V. Filippenko

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


We present a single epoch of high signal-to-noise ratio spectropolarimetry of the Type Ia supernova (SN Ia) 2004S taken 9 days after maximum light. The flux spectrum is normal, but with the additional presence of high-velocity (HV) line features in both Ca II and Fe II. The object shows continuum polarization at the 0.4% level in the red, a value which appears to be typical of SNe Ia. The continuum data are consistent with a 10% global asphericity in an axisymmetric geometry. Unlike previous observations of other SNe Ia with HV features, the HV features in SN 2004S show no strong polarimetric signature, though this may be due to the timing of our observations. Instead, the object shows line-polarization features (P ≤ 0.5%) that are rotated with respect to the axis of symmetry of the continuum. The line features are visible in Si II, Fe II, and Ca II, and appear to be narrowly confined in velocity space just above the photosphere. These polarization features are a result of compositional inhomogeneities in the ejecta. They may represent newly synthesized elements whose clumpy spatial distribution within the ejecta is distinct from that of the globally aspherical ejecta as a whole.

Original languageEnglish (US)
Pages (from-to)2227-2237
Number of pages11
JournalAstronomical Journal
Issue number6
StatePublished - 2008
Externally publishedYes


  • Polarization
  • Supernovae: individual (SN 2004S)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Fingerprint Dive into the research topics of 'Deviations from axisymmetry revealed by line polarization in the normal type Ia supernova 2004S'. Together they form a unique fingerprint.

Cite this