Other
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993mnras.265..471t&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Vol. 265, NO. 2/NOV15, P. 471, 1993
Other
38
Scientific paper
We present new photometric and spectroscopic observations of three type II supernovae with plateau light curves: SNe 1988A, 1988H and 1989C. From the new photometry of SN 1988A, we do not confirm the previous claim of a departure of the late-time light curve from ^56^Co radioactive decay and thus have no indication of the emergence of an additional source of energy. The early spectral evolution of SN 1988A seems rather normal, but for the appearance of a blue emissionlike feature on the Hα profile resembling a similar feature detected in SN 1987A. As in that supernova, this may be a manifestation of the appearance of radioactive ^56^Co above the photosphere. In the late-time spectrum (~450 d) several emission lines are identified. Apart from the lines of H, [OI], Ca II, Ca II], Na I, and Mg I], many of the other lines are probably due to Fe II and [Fe II]. In the late spectrum of the plateau SNII 1988H, we find that the positions of the peaks of the broad lines are blueshifted with respect to the rest-frame positions, and that the line profiles are asymmetric with a deficiency of radiation in the red wings. We suggest that this is evidence for dust formation within the supernova envelope. The fact that in SN 1988H this phenomenon occurs relatively early (about 300 d earlier than in SN 1987A) may be related to the greater expansion velocity and spectral evolution of this SN. SN 1989C has been proposed as a member of the class of SNII with narrow lines (SNIIn). We find that published magnitudes are heavily affected by the light of the nearby galaxy nucleus. The revised photometry and the new photometry place this SN among the plateau SNII with faster photometric evolution. Analysis of the spectroscopic observations shows a low expansion velocity, as determined from the Hα absorption, similar to the expansion velocity derived from Fe II lines. This may indicate an unusually small Hα optical depth for this SN. Also, we note that the narrow lines, present on the spectra, are more likely to be due to an underlying H II region.
Benetti Stefano
Cappellaro Enrico
Danziger Ivan John
Turatto Massimo
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