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 combine a number of powerful mathematical techniques to produce an effective method for treating multidimensional radiative transfer problems in complex atomic models without assuming local thermodynamic equilibrium (LTE). The approach is so efficient that multilevel two-dimensional (2D) modeling can now be performed with no more than a

The OJ-94 international collaboration has been observing the light curve of OJ287 intensely at radio, millimetric, infrared and visible wavelengths. We present a set of light curves for the 1993/94 observing season in 14 different bands from 4.8GHz to U. The monitoring covers an interval from August 1993 to the end of June 1994. The intensity of

We present the most recent results from our optical spectroscopy campaign on the X-ray Nova/Black Hole Candidate GRO J0422+32. Spectroscopy from the MMT during September 1994, when the system was at R=21 shows that the equivalent width of the H-alpha emission line is 150 Angstroms. Earlier Spectroscopy from March 1994, when the system was at R=20

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

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