We construct three extremely different scenarios of the star formation histories applicable to a sample of dwarf galaxies, based on either their present metallicity or their luminosity. The three possible scenarios imply different mechanical energy input rates, and these we compare with the theoretical lower limits established for the ejection of

We present spectropolarimetric evidence of convective collapse and destruction of magnetic flux by upward-moving fronts in the quiet Sun. The observational material consists of time series of the full Stokes vector of two infrared spectral lines emerging from regions associated with Ca II K network points. The amplitude of the circular polarization

We present a first study of truncation of the stellar disks of spiral galaxies in the near infrared. Observations of NGC 4013, NGC 4217, NGC 6504 and NGC 5981 were made with the CAIN NIR camera on the CST in Tenerife. This wavelength range provides the best description of the phenomenon, not only because extinction effects are minimized, but also

This is the second in a series of papers devoted to the study of a sample of 28 blue compact dwarf galaxies (BCDs). In the first paper, we presented the broadband observations in B, V, R, and I. Deep contour maps, surface-brightness profiles, and color profiles were used to analyze and discuss their morphology and structure. Here, we present new U

Gonçalves et al. (1996) showed the relevance of Alfvén heating in order to establish the stability of quasar broad-line region clouds in the intercloud medium due to thermal instability. Although, photoionization by the continuum radiation from the central source is the most important mechanism to heat and ionize the broad-line region, Alfvenic

Very Large Array7 neutral hydrogen observations of the shell elliptical galaxy NGC 3656 reveal an edge-on, warped minor-axis gaseous disk (MHI~2×109 Msolar) extending 7 kpc. H I is also found outside the optical image, on two complexes to the northeast and northwest that seem to trace one or two tidal tails, or possibly an outer broken H I disk or