2003IAUC.8159....2F

A. V. Filippenko, R. Chornock, and B. Swift, University of California, Berkeley; M. Modjaz, Harvard-Smithsonian Center for Astrophysics; R. Simcoe, California Institute of Technology; and M. Rauch, Carnegie Observatories, report that inspection of CCD spectra (range 320-1000 nm) obtained on 2001 June 29, July 16, and 27 UT with the Shane 3-m telescope at Lick Observatory, and on 2001 Aug. 17 with the Keck-I telescope (+ LRIS), reveal that SN 2001co (IAUC 7643) is a peculiar type-Ib or type-Ic supernova. Lines of H and He are absent, but the Ca II near-infrared triplet is very strong in emission, and the [Ca II] doublet near 730 nm is also present. No other clear emission or absorption features are visible in the combined, noisy spectrum. The spectral characteristics of this 'calcium-rich supernova' were unprecedented, and perhaps suspect (given the low signal-to-noise ratio), until Keck-I observations of SN 2003H (IAUC 8045, 8046), obtained on 2003 Feb. 28 UT by Filippenko and Chornock, revealed a very similar- looking spectrum: the only strong features are the [Ca II] and especially the near-infrared Ca II emission lines. SN 2003H had been classified as type Ib by Hamuy (IAUC 8047, 8049), but the Keck spectrum about 2 months after explosion is clearly very unusual; in normal type-Ib and type-Ic supernovae, prominent [O I] emission emerges in the nebular phase. Filippenko and Chornock add that inspection of CCD spectra (range 320-990 nm) obtained on June 29 with the Keck-I telescope (+ LRIS) reveals that SN 2003dg (IAUC 8113) and SN 2003dr (IAUC 8117) are peculiar type-Ib or type-Ic supernovae of the 'calcium-rich' variety described above, but evidently at a later phase than seen for SN 2001co and SN 2003H because the [Ca II] emission is stronger than the near-infrared Ca II triplet. [O I] 630.0- and 636.4-nm emission is much weaker than in normal type-Ib and type-Ic supernovae many months after the explosion.