F. Patat, European Southern Observatory (ESO); and A. Piemonte, Pontificia Universidad Catolica, report on their observations of SN 1998bw with the ESO 1.5-m telescope (+ Boller & Chivens spectrograph; 45-min exposure, range 315-1015 nm, resolution 1.5 nm) on May 23.39 UT at La Silla: "A full reduction of the CCD spectrogram shows no clear traces of He I lines (such as those at 587.6 and 667.8 nm), which were clearly detected in the type-Ib SN 1984L, a few weeks after maximum light (Harkness et al. 1987, Ap.J. 317, 355). Therefore, SN 1998bw should be classified rather as a type-Ic event. Nevertheless, there are some differences between SN 1998bw and known type-Ic supernovae. In particular, the whole spectrum strongly peaks around 540.0 nm, the O I 777.4-nm absorption is much broader than all other absorptions, and the Fe II features are weak, making this object unique. The most prominent features are identified as Ca II H and K, Si II 635.5-nm (possibly blended with C II 658.0-nm), O I 777.4-nm, the Ca II triplet (at 849.8, 854.2, and 866.2 nm), and a number of Fe II lines. The expansion velocities deduced from the minima of Ca II H and K and Si II 635.5-nm are 11 700 and 9100 km/s, respectively."
International Astronomical Union Circular
- Pub Date:
- May 1998