AAS 205th Meeting, 9-13 January 2005
Session 71 Supernovae
Poster, Tuesday, January 11, 2005, 9:20am-6:30pm, Exhibit Hall

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[71.08] Are Core-Collapse Supernovae Round?

D. C. Leonard, A. Gal-Yam, D. B. Fox (Caltech), R. Chornock, R. J. Foley, A. V. Filippenko, W. Li (UCB)

Since extragalactic supernovae (SNe) are spatially unresolvable during the very early phases of their evolution, explosion geometry has been a difficult subject to approach observationally. Sparking intense, recent interest in SN morphology has been the strong spatial and temporal association between some ``stripped-envelope'' SNe and gamma-ray bursts. These associations have fueled the proposition that some core-collapse SNe explode due to the action of a ``bipolar'' jet of material, as opposed to the conventional neutrino-driven mechanism. Such an explosion mechanism predicts severe distortions from spherical symmetry in the ejecta, and begs for a direct observational probe of early-time SN geometry.

Fortunately, geometric information is encoded in the polarization properties of supernova light, and extraordinary progress has been made in the past five years in the young field of supernova spectropolarimetry. For young core-collapse SNe, the fundamental result is that asphericity is ubiquitous, although the nature and degree of the asphericity vary considerably. The best predictor of core-collapse SN polarization appears to be the mass of the hydrogen envelope intact at the time of the explosion: those SNe that arise from progenitors with large envelopes have very low polarization (and, hence, low inferred asphericity), while those that result from progenitors that have lost part or all of their hydrogen layers prior to the explosion tend to show substantial polarization. Thus, the deeper we probe into core-collapse events, the greater the asphericity seems to be, suggesting a fundamentally asymmetric explosion with the asymmetry damped by the addition of envelope material. Recent results obtained as part of the Caltech Core-Collapse Project at Palomar Observatory, along with work carried out using the Keck 10-m and Lick 3-m telescopes, will be presented.

DCL is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-0401479.

The author(s) of this abstract have provided an email address for comments about the abstract: leonard@astro.caltech.edu

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