We have obtained HST-NICMOS observations of five of M31's most metal-rich globular clusters: G1, G170, G174, G177, and G280. For the two clusters farthest from the nucleus, G1 and G280, we statistically subtract the field population and estimate metallicities using K-(J-K) color-magnitude diagrams (CMDs). Based on the slopes of their infrared giant

Astronomers are always anxious to push their observations to the limit-basing results on objects at the detection threshold, spectral features barely stronger than the noise, or photometry in very crowded regions. In this paper we present a careful analysis of photometry in crowded regions and show how image blending affects the results and

We analyzed a 66 min time series of spatially highly resolved white light images to study the dynamics of photospheric light bridges which we assumed to be a restoration of the quiet surface inside sunspots. Similar decaying mechanisms were found as for normal photospheric dynamics for granulation.

The velocity field of the nearly face-on galaxy NGC 3631, derived from observations in the Hα line and Hi radio line, is analysed to study perturbations related to the spiral structure of the galaxy. We confirm our previous conclusion that the line-of-sight velocity field gives evidence of the wave nature of the observed two-armed spiral structure

Current models of the evolution of the known extrasolar planetary systems need to incorporate orbital migration and/or gravitational interactions among giant planets to explain the presence of large bodies close to their parent stars. These processes could also lead to planets being ingested by their parent stars, which would alter the relative

We explore the dependence of {T_eff}'s and colors of stellar models on the treatment of over-adiabatic convection, both in the atmosphere and in the interior. We compute main sequence, turnoff, and subgiant models for low metallicity stars (Z=2 10-4) using as boundary conditions two new sets of model atmospheres by the Wien group (Kupka \cite{kup96