We present a summary of Chandra monitoring observations of M31, and partial results of our HST program to search for UV counterparts to M31 X-ray Transients. The first 8 epochs of monitoring spread over nearly 2 years reveals more than a dozen transient sources, with peak luminosities ranging from 1 × 10^37ergs sec-1 to 3 × 10^38ergs sec-1. While

We report very intense and variable Hα emission (pseudoequivalent widths of ~180 and 410 Å) of S Ori 55, a probable free-floating, M9-type substellar member of the young σ Orionis open star cluster. After comparison with state-of-the-art evolutionary models, we infer that S Ori 55 is near or below the cluster deuterium-burning mass borderline

A two-component model of the solar photosphere is obtained from the inversion of the intensity profiles of 22 Fe I spectral lines for which very accurate atomic data (oscillator strengths, central wavelengths, and collisional broadening parameters) exist. The model is meant to describe the effects of convective motions in the solar photosphere. It

Observations with the Wide Field Cameras on BeppoSAX revealed seven type-I X-ray bursters that failed to exhibit significant levels of persistent emission. The constraints on the persistent luminosity simultaneous to the bursts are sometimes lower than what is commonly observed for type-I bursters. Therefore, a new class of objects is suggested

Through a high-resolution spectroscopic survey, we analyze the velocity field of 16 planetary nebulae with [WC]- or wels-type nuclei in comparison with 8 nebulae having other central star types. We found spectral evidence for finite turbulent velocities in [WC]-type planetary nebulae superimposed on an essentially constant expansion velocity

Not Available