Physics
Scientific paper
Sep 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aj....108.1002g&link_type=abstract
The Astronomical Journal, vol. 108, no. 3, p. 1002-1007
Physics
12
Photosphere, Spectral Emission, Stellar Envelopes, Stellar Mass Ejection, Stellar Physics, Stellar Radiation, Stellar Spectra, Stellar Winds, Supernovae, Color, Graphs (Charts), Helium, Hydrogen, Iron, Light Curve, Rates (Per Time), Spectrum Analysis, Tables (Data), Time Series Analysis
Scientific paper
Optical spectra covering the region 5500 to 7000 A with a resolution of 2.1 A were obtained during the first visual maximum of supernova 1993J. Thirteen spectra of the supernova were recorded between March 30.2 and March 31.5 (UT). They show narrow emission features of hydrogen, helium, and highly ionized iron. The H alpha line appears with a P-Cygni profile and its width decreases during the observing interval. All the sharp emission lines show a rapid drop in flux which can be attributed to circumstellar gas being overtaken by the expanding supernova envelope. Supplementing our data with spectra taken by the Isaac Newton Telescope Group, we find the temporal behavior of the circumstellar lines suggests that the mass-loss rate of the progenitor intensified about a year before the supernova explosion. A similar effect, but with a higher velocity wind, was seen in SN 1984E and suggests that enhanced mass-loss may precede some supernovae events by a few years or less. We derive a mass-loss rate during the year before the supernova of more than 3 x 10-4 solar mass/yr, or about ten times the rate estimated from radio techniques which sample more distant gas. The observed helium to hydrogen emission line flux ratio is larger than expected and implies that the helium abundance was enriched in the precursor wind, as might be expected from a star stripped of most of its hydrogen envelope. Broad, shallow, blue-shifted absorption features attributed to H alpha and He I 5875 A are also seen in the spectra and indicate the velocity of the expanding supernova photosphere to be approximately 14 000 km/s. The time series of individual spectra shows a rapid color evolution for the spectral range between 5500 and 6900 A, with the bluest continuum occurring between March 30.5 and 30.9 (UT).
Ann Hong Bae
Garnavich Peter M.
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