We study radiative transfer through a weakly polarizing medium, i.e., a medium in which the degree of polarization of the absorbed, retarded, and emitted light is always weak. In this case, the general radiative transfer equation for the Stokes parameters yields very simple formal solutions. The intensity does not depend on the polarization, and

In this poster we present statistical properties of a sample of Hii regions in the spiral galaxies NGC 4254, NGC 4321, NGC 5194, NGC 5248, NGC 5350 and NGC 6951. We have constructed catalogues of H ii regions using Hα and Hβ line images. In these catalogues we show Hα fluxes corrected for extinction, Hβ fluxes corrected for stellar absorption and

We present results of narrowband (Hα and adjacent continuum) and broadband (U, B, and V) optical CCD imaging together with high-resolution Hα spectroscopy of the blue compact Wolf-Rayet dwarf galaxies POX 4 and Tol 35. POX 4 has a fainter, irregular, and diffuse companion located 20.5" (4.7 kpc) along the minor axis of the galaxy, which is visible

Using the photoionization code CLOUDY, we compute photoionization models for the giant extragalactic H II region NGC 2363 and compare them with optical observational data. We mainly focus on F(Hβ), Ne, EW(Hβ), and the ratios of I(λ5007), I(λ4363), I(λ3727), I(λ6300), I(λ6720), and I(λ4686) to I(Hβ). We discuss the variations of the emission spectra

Based on optical and near-infrared ground-based spectroscopy and optical and near-infrared Hubble Space Telescope (HST) images, we confirm the classification of Hen 401 as a bipolar proto-planetary nebula. HST images reveal a highly elongated morphology, consisting of two main bipolar lobes of unequal surface brightness separated by a dark lane of

Recent studies have claimed that the Hubble sequence of late-type spirals, and spirals in general, is scale-free. Within the photometric data used in these works, a trend exists between morphological type and bulge profile shape such that late-type spiral bulges are described by an exponential luminosity profile, where-as the early-type spiral