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Letter to the Editor
Spectroscopy of 46 P/Wirtanen during its 1997 apparition
Received 4 November 1997 / Accepted 29 January 1998
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 at spectral resolutions of 12 and 18. 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 Af 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 Af/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 Af values combined with those obtained by photometry yield a fairly tight heliocentric activity dependence of 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.
Key words: comet spectrophotometry Wirtanen production rates dust
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Online publication: June 18, 1998