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Astron. Astrophys. 335, L37-L45 (1998)

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Letter to the Editor

Spectroscopy of 46 P/Wirtanen during its 1997 apparition

U. Fink 1, M.D. Hicks 2, R.A. Fevig 1 and J. Collins 1

1 Lunar and Planetary Laboratory, University of Arizona, Tucson AZ 85721, USA
2 JPL, 4800 Oak Grove Drive, MS 183-501E, Pasadena, CA 91109, USA

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 [FORMULA] at spectral resolutions of 12 [FORMULA] and 18[FORMULA]. 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 [FORMULA] 1028 molecules/sec. The continuum strength Af[FORMULA] was 129 cm while the production rates respectively of the parents of C2, CN and NH2 were 5.7, 3.2 and 5.6 [FORMULA] 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[FORMULA]/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[FORMULA] values combined with those obtained by photometry yield a fairly tight heliocentric activity dependence of [FORMULA] 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

Send offprint requests to: uwefink@lpl.arizona.edu

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© European Southern Observatory (ESO) 1998

Online publication: June 18, 1998