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C. Arpigny (U. Liège), A.L. Cochran (U. Texas), E. Jehin (ESO), J. Manfroid (U. Liège, Research Director FNRS (Belgium)), D. Hutsemékers (U. Liège, Research Associate FNRS (Belgium)), J.-M. Zucconi (Obs. Besancon), M. Endl, W.D. Cochran (U. Texas), R. Schulz (ESA)
High-resolution (R~60,000) spectra of the Halley-type comet 122P/1995 S1 de Vico (Period 74 years) and the ``intermediate-period" comet 153P/2002 C1 Ikeya-Zhang (P~370 yr) were obtained with the 2DCoude spectrograph at the 2.7-m Harlan J. Smith telescope of the McDonald Observatory. These comets were within 1 AU from the Sun (0.66 and 0.92 AU, respectively). The spectra display CN (0,0) bands indicating an anomalous 14N/15N isotope ratio, in the sense that it is close to half the value in Earth's atmosphere (the so-called ``Solar system value") and about half that obtained in comet Hale-Bopp from sub-millimeter measurements on HCN, generally believed to be the main parent of CN. Similar conclusions had been reached for C/1995 O1 (Hale-Bopp), an ``old long-period", and for C/2000 WM1 (LINEAR), a ``young long-period" comet.
As suggested by Arpigny et al. (2003), this apparent abundance anomaly points towards the existence of other unknown parent(s) of CN, with an even higher 15N excess. Organic compounds like those found in interplanetary dust particles (IDPs) are good candidates. The similarity between comets of different dynamical ages is pointed out.
1 Research Director FNRS (Belgium) 2 Research Associate FNRS (Belgium)
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.