Assuming that photoionization is the self-limiting process for continued star formation, we estimate the maximum number of massive (OB) stars that can form within a molecular cloud. The most efficient cloud destruction mechanism in the early stages of H II region evolution is the evaporation of the cloud by stars located near the cloud boundary

We present bidimensional spectroscopy of the circumnuclear region of the Seyfert galaxy NGC 3227. The physical and kinematical characteristics of the two gaseous components reported recently by Mediavilla & Arribas are discussed. One of the components seems to be directly related to activity. We propose that it represents gas streaming from the

This work quantifies the influence of the terrestrial atmosphere on the instrumental polarization (IP) of telescopes. Our numerical simulations show that seeing mostly induces a random crosstalk between Stokes parameters. The main contamination affects the linear polarization signals and is due to mixing with intensity. In general, circular

The results of a UBVR photometric study in the field of the open cluster IC 1311 are presented. A comparison with previously published results on NGC 7044, based on measurements secured during the same observing run, leads to a self-consistent constraints to the parameters of the cluster. The location of selected samples of giant and unevolved

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We present the results of the study of visible (BVRI) intra-night variability of the BL Lac object OJ287. The observations were carried out on a total of 29 nights during the period November 1993-October 1994, with only nights with at least 4 observations being included. Three telescopes were used for the study: the 1m Jacobus Kapteyn Telescope and