Spectroscopy of 46 P / Wirtanen during its 1997 apparition

Comet 46P/Wirtanen was observed during five observing runs around its perihelion passage from 1997 January 28 to June 02. The spectra acquired extend from 5200 to 10000 Å at spectral resolutions of 12 Å and 18Å. A total of 16 spectral averages, each comprising about 40 minutes of integration time, were obtained. The production rate of H2O near perihelion averaged 2.7 × 1028 molecules/sec. The continuum strength Afρ was 129 cm while the production rates respectively of the parents of C2, CN and NH2 were 5.7, 3.2 and 5.6 × 1025 molecules/sec. Our estimated error for all these quantities is 20%. The production rate ratios relative to water can be compared to our larger sample of comets (Fink & Hicks 1996) with the following results: the C2 and CN abundance ratios are slightly below average but the NH2 ratio is definitely enhanced putting P/Wirtanen among the top few comets in that category. Its Afρ/H2O ratio is very close but slightly below the median of our comet sample. Reduced to 1 AU P/Wirtanen ranks near the 40% level of our ordered list of the H2O production rates of 20 comets. If the production rate of water is combined with P/Wirtanen’s estimated radius of 0.6 km, it implies that virtually the whole surface area of the comet is active. Our measured Afρ values combined with those obtained by photometry yield a fairly tight heliocentric activity dependence of r−3.8 with no pre-post perihelion asymmetry. This agrees well with the general heliocentric brightness dependence of Jupiter family comets. Taking all this data together, P/Wirtanen appears to be a rather typical member of the Jupiter family of comets.