AAS 204th Meeting, June 2004
Session 63 Exploding Stars
Poster, Wednesday, June 2, 2004, 10:00am-7:00pm, Ballroom

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[63.08] SN~2003du: Signatures of the Circumstellar Environment in a Normal Type~Ia Supernova?

C. L. Gerardy (McDonald Observatory, Univ. of Texas, Austin), P. Höflich (Univ. of Texas, Austin), R. A. Fesen (Dartmouth College), G. H. Marion (Univ. of Texas, Austin), K. Nomoto (Univ. of Tokyo), R. Quimby (Univ. of Texas, Austin), B. E. Schaefer (Louisiana State Univ.), L. Wang (Lawrence Berkeley Laboratory), J. C. Wheeler (Univ. of Texas, Austin)

We present observations of the Type Ia supernova 2003du obtained with the Hobby-Eberly Telescope (HET) and report the detection of a high-velocity component in the \ion{Ca}{2} infrared triplet near 8000~Å, similar to features observed in SN~2000cx and SN~2001el. This feature exhibits a large expansion velocity (\approx 18,000 km~s-1) which is nearly constant between -7 and +2 days relative to maximum light, and disappears shortly thereafter. Other than this feature, the spectral evolution and light curve of SN~2003du resemble those of a normal SN~Ia.

We consider possible origins for this high-velocity \ion{Ca}{2} feature and find that it can be caused by a dense shell formed when circumstellar material of solar abundance is overrun by the rapidly expanding outermost layers of the SN ejecta. Model calculations show that the optical and infrared spectra are remarkably unaffected by the circumstellar interaction and the resulting shell. In particular, no hydrogen lines are detectable in either absorption or emission after the phase of dynamic interaction. The only qualitatively different features in the model spectra are the strong, high velocity feature in the \ion{Ca}{2} IR-triplet around 8,000~Å, and a somewhat weaker \ion{O}{1} feature near 7,300~Å. The Doppler shift and time evolution of these features provides an estimate for the amount of accumulated matter and also an indication of the mixing within the dense shell.

We apply these diagnostic tools to SN~2003du and infer that about 2 \times 10-2M\odot of solar abundance material may have accumulated in a shell prior to the observations. The early light curve implies that the circumstellar material was very close to the progenitor system, perhaps originating in an accretion disk, Roche lobe, or common envelope.

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