By describing the dynamical evolution of a test charged particle in the presence of an electromagnetic field and a succession of infinitesimal Lorentz boosts and rotations it is possible to obtain the Lorentz force of electrodynamics. A consequence of this heuristic derivation at the classical level is that, given the existence of electric and

Intermediate-resolution optical spectra of the X-ray transient J0422+32, obtained during the 1993 December mini-outburst, show a strong modulation in radial velocities and equivalent widths of all the emission lines, with a period of 0.2127+/-0.0013d (5.1h). This modulation is in good agreement with the photometric period of 0.2121d reported during

Bolometric fluxes for 118 dwarfs and subdwarfs with 4000K less than Teff less than 7000K and +0.5 less than (Fe/H) less than -3.5 are derived by integrating UBVRIJHK photometry. For these stars (typical of the galactic and globular cluster main sequences) at least 80% of the energy emitted is measured by those bands. A grid of theoretical model

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We report the detection of an orbital, ellipsoidal modulation at a period of 16.8h for V2107 Oph (Nova Ophiuchi 1977, H1705-25), from R-band photometry. From this period and the observed magnitude, constraints on the distance are calculated (2.0-8.4 kpc), which are consistent with that obtained previously from X-ray observations (3kpc). By

We first discovered the presence of a particularly massive cloud in the neighborhood of the Sun, close to the Galactic plane in the direction of Perseus, toward l = 150 deg, b = -10 deg, using interstellar absorption by the 7699 A resonance line of K I (Trapero et al. 1992). In the present investigation we show the results of mapping the cloud in