We classify non-trivial (non-central) extensions of the group $Diff^+(S^1)$ of all diffeomorphisms of the circle preserving its orientation and of the Lie algebra $Vect (S^1)$ of vector fields on $S^1$, by the modules of tensor-densities on $S^1$. The result is: 4 non-trivial extensions of $Diff^+(S^1)$ and 7 non-trivial extensions of $Vect (S^1)$

EN ESTE TRABAJO SE PRESENTAN LOS RESULTADOS DEL ANALISIS DE OBSERVACIONES FOTOMETRICAS Y ESPECTROSCOPICAS DE SIETE DE LAS OCHO BINARIAS QUE CONSTITUYEN EL SUBGRUPO DE SISTEMAS RS CVN DE PERIODO CORTO, ASI COMO DE OTROS DOS SISTEMAS DE PERIODO MAS LARGO PERTENECIENTES AL SUBGRUPO LLAMADO "CLASICO" DE LOS SISTEMAS RS CVN. LAS OBSERVACIONES

IAUC 6065 available at Central Bureau for Astronomical Telegrams.

A procedure to compute meteoroid spatial number densities from photographs is presented. It follows from the visual method of Koschack and Rendtel with slight changes. Some parameters are recomputed and hints are given on how to produce useful photographic observations. Finally, an analysis of the expected errors is performed.

A sample of actively star forming H II galaxies has been observed in the radio continuum and several optical bands. These galaxies are currently undergoing very active star formation and have been selected on the basis of strong radio continuum emission. Most of the galaxies are irregular and have been associated with merger or interaction events

We present Very Large Array (VLA) radio continuum and Infrared Astronomy Satellite (IRAS) far-infrared (FIR) observations of 16 low luminosity galaxies of mostly low surface brightness. All galaxies had previously claimed single dish radio continuum detections. However, at the frequencies of our observations (1.49 and 8.48 GHz), we find significant