The energy budget of all known optical jets is discussed. It is found that to power the extended radio lobes of radio galaxies, the jet bulk motion on kpc scales must be relativistic, on average. Based on various constraints, a ``most probable'' region centered around Γbulk~7.5 and /θ~20° is found. Because of the consequent relativistic beaming

A systematic study of the linear thermal stability of a medium subject to cooling, self-gravity, and thermal conduction is carried out for the case when the unperturbed state is subject to global cooling and expansion. A general, recursive WKB solution for the perturbation problem is obtained that can be applied to a large variety of situations in

An analysis of Hα and Hβ spectra in a sample of 30 cool dwarf and subgiant stars is presented using MARCS model atmospheres based on the most recent calculations of the line opacities. A detailed quantitative comparison of the solar flux spectra with model spectra shows that Balmer line profile shapes, and therefore the temperature structure in the

IAUC 7868 available at Central Bureau for Astronomical Telegrams.

We present high resolution spectroscopic data of the two giant extragalactic H II regions NGC 5461 and NGC 5471 in M101, which have been obtained with the 2.1-m telescope of the Observatorio Astronómico Nacional in San Pedro Martir, Baja California. We measured the intensities of several H and He recombination lines, and of forbidden lines of a

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