Spectropolarimetry of the Peculiar Type Ia SN 2005hk

Authors:
  • RCRyan Chornock
    Ryan Chornock
  • AFAlexei V. Filippenko
    Alexei V. Filippenko
  • DBDavid Branch
    David Branch
  • RFRyan J. Foley
    Ryan J. Foley
  • SJSaurabh Jha
    Saurabh Jha
  • WLWeidong Li
    Weidong Li
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Abstract
We present Keck spectropolarimetry of the unusual type Ia supernova (SN Ia) 2005hk several days before maximum light. An analysis of the high signal-to-noise-ratio total-flux spectrum shows the object's extreme similarity to the peculiar SN 2002cx. SN 2005hk has an optical spectrum dominated by Fe III lines and only weak lines of intermediate-mass elements, unlike a normal SN Ia at this epoch. The photospheric velocity measured from the minima of strong absorption lines is very low for an SN Ia (~6000 km s^{-1}), solidifying the connection to SN 2002cx. The spectrum-synthesis code Synow was used to identify some of the lines, but many weak features remain unidentified. The spectropolarimetry shows a low level of continuum polarization (~0.4%) after correction for the interstellar component and only a weak Fe III line feature is detected. The level of continuum polarization is normal for an SN Ia, implying that the unusual features of SN 2005hk cannot be readily explained by large asymmetries.