3–14 Micron Spectroscopy of Comets C/2002 O4 (Honig), C/2002 V1 (NEAT), C/2002 X5 (Kudo‐Fujikawa), C/2002 Y1 (Juels‐Holvorcem), and 69P/Taylor and the Relationships among Grain Temperature, Silicate Band Strength, and Structure among Comet Families

Abstract

We report 3-13 μm spectroscopy of four comets observed between 2002 August and 2003 February: C/2002 O4 (Honig) on 2002 August 1, C/2002 V1 (NEAT) on 2003 January 9 and 10, C/2002 X5 (Kudo-Fujikawa) on 2003 January 9 and 10, and C/2002 Y1 (Juels-Holvorcem) on 2003 February 20. In addition, we include data obtained much earlier on 69P/Taylor (1998 February 9) but not previously published. For comets Taylor, Honig, NEAT, and Kudo-Fujikawa, the silicate emission band was detected, being approximately 23%, 12%, 15%, and 10%, respectively, above the continuum. The data for comet Juels-Holvorcem were of insufficient quality to detect the presence of a silicate band of comparable strength to the other three objects, and we place an upper limit of 24% on this feature. The silicate features in both NEAT and Kudo-Fujikawa contained structure indicating the presence of crystalline material. The shape of the silicate feature at a projected distance of 1900 km from the nucleus of Kudo-Fujukawa was nearly identical to that centered on the nucleus, indicating that the grain size population had not been measurably modified by the time it had reached that distance. Combining these data with those of other comets, we confirm the correlation between silicate band strength and grain temperature of Gehrz & Ney and Williams and coworkers for dynamically new and long-period comets, but the majority of Jupiter family objects may deviate from this relation. Despite the weakness of the silicate band in Kudo-Fujikawa, its structure resembles the bands seen in dynamically new and long-period objects with substantially stronger features. The limited data available on Jupiter family objects suggest that they may have silicate bands that are slightly different from the former objects. Finally, when compared to the silicate emission bands observed in pre-main-sequence stars, the dynamically new and long-period comets most closely resemble the more evolved stellar systems, while the limited data (in quantity and quality) on Jupiter family objects seem to suggest that these have spectra more like the less evolved stars. Higher quality data on a larger number of Jupiter family objects are needed to confirm (or reject) this trend.