The Astronomical Journal
Near-infrared spectra (0.95 – 2.4 μm) of the Cassiopeia A and Kepler supernova remnants (SNRs) are presented. Low-dispersion (R ≈ 700) spectra were obtained for five bright fast-moving ejecta knots (FMKs) at two locations on the main shell and for three bright circumstellar knots (QSFs) near the southwest rim of Cas A. The main shell FMKs in Cas A exhibit a sparse near- infrared spectrum dominated by [S II] 1.03 μm emission with a handful of other, fainter emission lines. Among these are two high-ionization silicon lines, [Si VI] 1.96 μm and [Si X] 1.43 μm, which have been detected in AGNs and novae but never before in a supernova remnant. The near-infrared spectra of circumstellar QSFs in Cas A show a much richer spectrum, with strong He I 1.083 μm emission and over a dozen bright [Fe II] lines. Observed [Fe II] line ratios indicate electron densities of 5 – 9 × 104 cm−3 in the QSFs. The Cas A QSF data are quite similar to the observed spectrum of a bright circumstellar knot along the northwest rim of the Kepler SNR, which also shows strong He I and [Fe II] emission with a measured electron density of 2.5 – 3 ×104 cm−3. Finally, we present J- and K-band images of Cas A. The K-band image shows faint diffuse emission which has no optical or mid-infrared counterpart but is morphologically similar to radio continuum maps and may be infrared synchrotron radiation.
Gerardy, Christopher L. and Fesen, Robert A., "Near-Infrared Spectroscopy of the Cassiopeia A and Kepler Supernova Remnants" (2001). Open Dartmouth: Faculty Open Access Articles. 2109.