Near infrared spectra of SN 1987A: Days 936 to 1445
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We present 1-2.5 m spectra of SN 1987A taken 936, 1058, 1109, 1294, and 1445 days after core collapse. The low resolution (/150) spectra show many lines from neutral and singly ionized species, most notably Fe and Si. We also tentatively detect Co emission. Measurements of several [Fe II] lines suggest that on day 936 the electron density in the Fe II emitting region was 104.00.3 cm-3. This density and the intensity of the [Fe II] lines suggest that the electron temperature on day 936 was between 1900 and 3000 K. We find that the electron temperature throughout these epochs is greater than 1500 K, which seems to indicate that the Fe escaped an infrared catastrophe through day 1500. The total mass of Fe estimated from our measurements is less than 0.04 Script M sign, most of which if Fe0 and lower than many theoretical expectations. We also show that the Fe II and the observed H I emission lines probably come from different regions in the ejecta of the supernova.
