Activity of comet 103P/Hartley 2 at the time of the EPOXI mission fly-by

Comet 103P/Hartley~2 was observed on Nov. 1-6, 2010, coinciding with the fly-by of the space probe EPOXI. The goal was to connect the large scale phenomena observed from the ground, with those at small scale observed from the spacecraft. The comet showed strong activity correlated with the rotation of its nucleus, also observed by the spacecraft. We report here the characterization of the solid component produced by this activity, via observations of the emission in two spectral regions where only grain scattering of the solar radiation is present. We show that the grains produced by this activity had a lifetime of the order of 5 hours, compatible with the spacecraft observations of the large icy chunks. Moreover, the grains produced by one of the active regions have a very red color. This suggests an organic component mixed with the ice in the grains.Comment: 11 pages, 7 figures, Icarus in pres

A System For The Monitoring Of The Mesospheric Sodium Layer Using A Magneto-Optical Filter

. A general use of the adaptive optics require an artificial guide star created by focusing a laser beam tuned to the sodium D 2 line. We propose here a system to monitor the column density of the mesospheric sodium layer which is based on the sodium magneto-optical filter (MOF) already widely used in solar observations. The principal characteristics of this system are high transmission and high spectral resolution which allow to perform measurements in minutes on a relatively small (50 cm) telescope, where the MOF can easily mounted due to its compactness. 1. Introduction Adaptive optics (AO) systems for atmospheric turbulence compensation require a bright reference star for measuring and correcting wavefront distortion. The star must be within a small field of view (the isoplanatic patch) of the object of interest, which varies from arcseconds to tens of arcseconds increasing with the wavelength of observation. While some sources are bright enough, most astronomical objects are too ..