2004IAUC.8387....3P

F. Patat and G. Pignata, European Southern Observatory; and S. Benetti, Istituto Nazionale di Astrofisica, on behalf of the ERTN, report that a fully reduced spectrum (range 320-850 nm; resolution 1.6 nm) of SN 2004dt (cf. IAUC 8386), obtained on Aug. 13.17 UT by J. Aceituno at the Calar Alto Observatory 2.2-m telescope (+ CAFOS), shows it to be a type-Ia supernova with some unusual features. In particular, there is a strong P-Cyg line whose absorption is measured at 392.4 nm (rest frame), tentatively identified as C II 426.7-nm, with an implied expansion velocity of about 24100 km/s. If this identification is correct, the other intense C II 657.6- 658.3-nm transitions are blended with the Si II 635.5-nm, which indeed appears very broad, intense, and with an asymmetric absorption trough. Particularly pronounced, with a broad symmetric P-Cyg profile, is also the O I 777.6-nm transition, from which an expansion velocity of about 16800 km/s is deduced. In a normal type-Ia supernova, these rather high expansion velocities (the Ca II H and K line gives about 22200 km/s) would indicate a very early phase. Other intense lines visible in the spectrum are from Fe III and Si III.