Serendipitous occultation of U0975-07195164 by 9P/Tempel 1 witnessed from LaSilla

Abstract

Comet 9P/Tempel 1 was systematically monitored by ESO after re-appearance in January 2005. Routinely various narrow-band filters in the 10 μm window were used with TIMMI2 at ESO's 3.6 m telescope. Quasi-simultaneously, the comet was also observed with an R-band filter from ESO's 3.5 m NTT. In the February 2005 period, the comet happened to pass accidentially rather close to a reasonably bright field star, unfortuately in non-photometric conditions. The NTT observing set-up was immediately changed from optical imaging to low-resolution spectroscopy, so that the reddening of the stellar light of this star by the inner coma could be measured with high precision. In combination with the thermal-IR data this may help for unique constraints on the dust particle size distibution as well as for the optical constants of the dust. © 2009 Springer-Verlag Berlin Heidelberg.