The spectrum of Ikkeya-Seki (1965f)

At solar distances greater than 0.4 a u. before and after perihelion, the spectrum of comet Ikeya-Seki (196Sf) contained the usual cometary emissions due to CH, CN, C1, and C3. On October 22, 1965,1.6 days after perihelion, emission lines due to [0 I], Na I, K I, Ca II, Cr I, Mn I, Fe I, Ni I, Cu I, and CN were present. A curve-of-growth analysis of the Fe I emission lines leads to a formal excitation temperature of 4500 K. Evidence is found for fluorescence in the spectra of Fe I and Ni I. An upper limit of about 2600 K is obtained for the excitation temperature derived from lines of Na I and K I. The apparent abundance ratio K I/Na I is low and the ratio Cu I/Fe I is unaccountably high in the comet relative to the Sun, meteorites, and Earth's crust. In view of numerous uncertainties, smaller abundance anomalies for other elements cannot be regarded as well established. The absence of the Al I resonance lines is attributed to photo-ionization. Lifetimes against photo-ionization may control the dimensions of the region defined by surface brightnesses in the emission lines of neutral metals. Surface-brightness distributions and estimates of absolute intensities for lines of Fe I and Na I lead to volume densities of 180 and 8000 cm-3 for Fe I and Na I, respectively, near the nucleus of the comet. Intensity distributions in the P- and R-branches of the CN (0,0) band show the mutilating effects due to fluorescence excited by solar radiation. A rotational temperature of 760 K is derived from the CN lines on October 22.