It has been suggested that Earth's current supply of water was delivered by asteroids, some time after the collision that produced the Moon (which would have vaporized any of the pre-existing water). So far, no measurements of water ice on asteroids have been made, but its presence has been inferred from the comet-like activity of several small

Variability is a key property of ultracool dwarfs as it may induce physical noise that limits the accuracy of radial velocities. In this paper we report on our current activities in the study of variability in ultracool dwarfs.

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The CCD UBV(RI)C observations of this paper have been made exclusively with the 0.84-m f/15 Ritchey-Chretien telescope at SPM, during the night of 2001 June 25/26 for the open cluster Be 80, and the nights 2002 February 6/7 and 8/9 for the clusters NGC 2192 and Be 15, respectively. (3 data files).

We numerically investigate the excitation and temporal evolution of oscillations in a two-dimensional coronal arcade by including the three-dimensional propagation of perturbations. The time evolution of impulsively generated perturbations is studied by solving the linear, ideal magnetohydrodynamic (MHD) equations in the zero-β approximation. As we