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An analysis of the behavior of the dust coma of the Comet C/1999 S4 (LINEAR) from visible and infrared images acquired shortly before and after the disruption of the comet's nucleus is presented. During the predisruption phase, the overall dust production increased by a factor of 11 in two steps; an initial outburst occurred between July 18 and 19

IAUC 7889 available at Central Bureau for Astronomical Telegrams.

We report transmission measurements at cryogenic temperatures for 4 broad-band filters of the Mauna Kea Observatories (MKO) near-infrared filter set and 5 narrow-band filters. The spectral scans were collected using the multi-mode IR instrument of the TNG telescope (NICS) in which these filters are permanently mounted and commonly used for

The multiwavelength emission spectrum and associated velocity field of the Seyfert prototype NGC 4151 is modeled. Since the thirties NGC 4151 has been the subject of extensive modeling, nuclear photoionization being the basic approach considered by all authors. HST data has impressively revealed the existence of a large range of velocities (100

In this paper we make a quantitative study of the hypothesis that the diffuse Hα emitted from the discs of spiral galaxies owes its origin to the ionizing photons escaping from H SHAPE II regions. The basis of the models is the assumption that a fraction of the Lyman continuum (Lyc) luminosity from the OB stars within each H SHAPE II region escapes