Here we make a new study of the behaviour of the NaI/KI column density ratio in the interstellar medium, using a sample of new observations of 28 stars obtained at the Nordic Optical Telescope (NOT) in 1996 and 1997, and previously published observations (obtained by some of the authors) of 21 stars. The sightlines cover a range of distances and

Not Available

An accurate determination of photospheric solar abundances requires detailed modeling of the solar granulation and accounting for departures from local thermodynamical equilibrium (LTE). We argue that the forbidden C I line at 8727 Å is largely immune to departures from LTE and can be realistically modeled using LTE radiative transfer in a time

We have designed, constructed, and put into operation a large-area CCD camera that covers a large fraction of the image plane of the 1 m Schmidt telescope at Llano del Hato in Venezuela. The camera consists of 16 CCD devices arranged in a 4×4 mosaic covering 2.3d×3.5d of sky. The CCDs are 2048×2048 LORAL devices with 15 μm pixels. The camera is

We report an increase of more than 0.2 mag in the optical brightness of the leading image (A) of the gravitational lens Q0957+561, detected during the 2000 September to 2001 June monitoring campaign (2001 observing season). The brightening is similar to or even greater than the largest change ever detected during the 20 yr of monitoring of this

Using photometric and redshift data for the Virgo and Coma Clusters, we present evidence for a correlation between the light concentration of elliptical galaxies (including dwarf ellipticals) and the local three-dimensional (i.e., nonprojected) density of the clusters: more concentrated ellipticals are located in denser regions. The null hypothesis