Properties of the nuclei and comae of 13 ecliptic comets from?Hubble Space Telescope snapshot observations

摘要

Context. Knowledge of the size distribution ofcometary nuclei and, more generally, of their physical properties isimportant for constraining models of the formation and evolution of theSolar System. Aims. We report on our on-going effort to determinethe ensemble properties of comets based on our success in detecting thenuclei of active comets with the Hubble Space Telescope (HST). Methods. During cycle 8 (July1999 toJune2000), we observed 13 ecliptic comets with the planetarycamera2 through at least two filters (Vand R) and up to four (B, V,R, I) for the brightest ones.The 30minof HST observational time devoted to each comet did not permit a properdetermination of light curves, so our ``snapshot'' observations yieldeffective radii, not shapes. Results. Assuming spherical nuclei with a geometricalbedo of 0.04 for the Rband (except0.024 for 10P/Tempel2, as independently measured) and a phaselaw of 0.04mag/deg, we obtained the following effectiveradii: 4P/Faye: 1.77km, 10P/Tempel 2: 5.98km,17P/Holmes: 1.71km, 37P/Forbes: 0.81km 44P/Reinmuth2: 1.61km, 50P/Arend: 0.95km, 59P/Kearns-Kwee:0.79km, 63P/Wild1: 1.46km, 71P/Clark:0.68km, 84P/Giclas: 0.90km, 106P/Schuster:0.94km, 112P/Urata-Niijima: 0.90km,114P/Wiseman-Skiff: 0.78km. In our present sample, eight outof thirteen nuclei have sub-kilometer radii. The average color of theobserved nuclei is ,which is significantly redder than the Sun. We determined the dustactivity parameter of their coma in the R band, and estimated the dustproduction rates. The average reflectivity gradient of the dust comaeof six comets is%perk?.Key words: comets: general - methods: dataanalysis - techniques: photometric - techniques: image processing -telescopes - solar system: general