Type Ib SN 1999dn as an example of the thoroughly mixed ejecta of Ib supernovae

• Published in: Monthly notices of the Royal Astronomical Society 2014-03, Vol.438 (4), p.2924-2937
• Main Authors: Cano, Zach, Maeda, Keiichi, Schulze, Steve
• Format: Article
• Language: English
• Subjects: Astronomy; Helium; Light; Supernovae
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stt2400

We present the results of modelling archival observations of Type Ib SN 1999dn. In the spectra, two He i absorption features are seen: a slower component with larger opacity, and a more rapid He i component with smaller opacity. Complementary results are obtained from modelling the bolometric light curve of SN 1999dn, where a two-zone model (dense inner region, and less dense outer region) provides a much better fit than a one-zone model. A key result we find is that roughly equal amounts of radioactive material are found in both regions. The two-zone analytical model provides a more realistic representation of the structure of the ejecta, including mixing and asymmetries, which offers a physical explanation for how the radioactive material is propelled to, and mixed within, the outer regions. Our result supports the theoretical expectation that the radioactive content in the outflow of a Type Ib supernova (SN) is thoroughly mixed. We fit our model to six additional SNe Ibc, of which the majority of the SNe Ib are best described by the two-zone model, and the majority of the SNe Ic by the one-zone model. Of the SNe Ic, only SN 2007gr was best fitted by the two-zone model, indicating that the lack of helium spectral features for this event cannot be attributed to poor mixing.