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American Astronomical Society, Astrophysical Journal, 1(653), p. 490-502, 2006

DOI: 10.1086/508250

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Premaximum Spectropolarimetry of the Type Ia SN 2004dt

Journal article published in 2006 by Lifan Wang, Dietrich Baade, Peter Höflich, J. Craig Wheeler, J. Craig Wheeler, Koji Kawabata, Alexei Khokhlov, Ken'ichi Nomoto, and Ferdinando Patat ORCID
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

We report observations of SN 2004dt obtained with the Very Large Telescope (VLT) of the European Southern Observatory (ESO) on 2004 August 13.30, when the supernova was more than a week before optical maximum. SN 2004dt showed strong lines of O I, Mg II, Si II, and Ca II, with typical velocities of absorption minimum around 17,000 km s-1. The line profiles show material moving at velocities as high as 25,000 km s-1 in these lines. The observations also reveal absorption lines from S II and Si III with a velocity of only 11,000 km s-1. The highest velocity in the S II features can be traced to about 15,000 km s-1, much lower than those of O, Mg, Si, and Ca. SN 2004dt has a polarization spectrum unlike any previously observed. The variation of the polarization across some Si II lines approaches 2%, making SN 2004dt the most highly polarized SN Ia ever observed. In contrast, the strong line of O I at 777.4 nm shows little or no polarization signature. The degree of polarization points to a silicon layer with substantial departure from spherical symmetry. A geometry that would account for the observations is one in which the distribution of oxygen is essentially spherically symmetric, but with protrusions of intermediate-mass elements within the oxygen-rich region.