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Spectrum change of bright SN 2012fg in NGC 2857

ATel #4520; S. Fabrika, T. Fatkhullin, A. Valeev, A. Moskvitin, A. Vinokurov, O. Sholukhova (Special Astrophysical Observatory, Russia)
on 26 Oct 2012; 10:36 UT
Credential Certification: Sergei Fabrika (fabrika@sao.ru)

Subjects: Optical, Supernovae

We have taken new spectrum of the Supernova in NGC 2857 (PSN J09243795+4921320) discovered originally in ATel #4459 and known as SN 2012fg (ATel #4466, CBET #3253). Our previous spectrum taken 8 days before has been described in ATel #4496. The new spectrum has been taken with SCORPIO spectrograph of the Russian telescope BTA on 2012 Oct. 23.07 UT. Spectral resolution was 6 A, spectral range 3800-8000 A. The Supernova has changed its spectrum notably. Broad hydrogen absorption lines became deeper, but the line centers stay at the same positions, ~-9600 km/s relatively the galaxy (the galaxy redshift z=0.01624, ATel #4496). Strong and asymmetric H-alpha emission line was appeared with FWHM~9000 km/s. Strong and broad FeII absorption blends were appeared at ~4470, 5120 and 6290 A. We detect other absorption lines: HeI 5876 A, SiII 5957, 5978 A, and, possibly, CaII HK and NaI D1,2. Two additional absorption features at 4920 and 4990 A are present. The spectrum is not such blue as it was 8 days ago, we find its maximum (F_lambda) at 4000-4400 A. At the same time the star became fainter on only 0.1 mag in V band. Using correlation method of the SNID code (S. Blondin and J.L. Tonry, ApJ 666, 1024, 2007) we have found the spectrum closely fits the SN1993J one a few days before its maximum.