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Abstract
Distant supernovae (SNe) are not spatially resolved when observed from Earth, but these explosions result in ejecta with complicated spatial structures, including global deviations from spherical symmetry, chemical inhomogeneities, and substructure due to clumps. The purpose of this dissertation is to indirectly study the geometry of supernovae using the technique of optical spectropolarimetry.
SN 2004S is a normal SN Ia observed nine days after maximum light and shows a low level of continuum polarization, 0.4%, which is typical for a SN Ia. Line polarization features are present and are rotated with respect to the continuum, indicating that the silicon, iron, and calcium distributions are distinct from the aspherical continuum photosphere. SN 2005hk is shown to be very spectroscopically similar to the peculiar SN la 2002cx. The continuum polarization level is normal and only weak Fe III line polarization features are present, indicating that the peculiarities of this subclass of SNe Ia are not a result of strong asphericities.
SNe II have been shown in the past to have relatively spherical outer envelopes, but with evidence for increasing asphericity with time as the core is exposed. We present late-time spectropolarimetry of three SNe IIP (SNe 2006my, 2006ov, and 2007aa) which all show large polarizations (0.82-1.56%), indicative of large asphericities in their cores. SNe IIP are the most common form of core-collapse SNe, so our results imply that all core-collapse SNe have highly aspherical cores.
We also present a detailed optical and near-infrared spectral sequence of the core-collapse SN 2008ax starting two days after shock breakout. SN 2008ax exploded with a very low-mass hydrogen envelope that produced strong Balmer absorption lines that rapidly disappeared as the object came to exhibit the spectra of a SN Ib. Two epochs of early-time spectropolarimetry, 6 and 9 days after shock breakout, revealed very strong line polarization modulations (up to 3.4% at Hα), which were not aligned with each other and indicate that SN 2008ax had a complex geometry. Late-time spectropolarimetry and the nebular line profiles show that the inner ejecta were also highly aspherical.
