The spectra of the Sloan Digital Sky Survey (SDSS) are being used to construct a catalogue of QSO absorption lines, for use in studies of abundances, relevant radiation fields, number counts as a function of redshift, and other matters, including the evolution of these parameters. The catalogue includes intervening, associated, and BAL absorbers, in order to allow a clearer definition of the relationships between these three classes. We describe the motivation for and the data products of the project to build the SDSS QSO absorption line catalogue.

We present results from an ongoing program to probe the dense central parts of Galactic globular clusters using multicolor Hubble Space Telescope images (WF/PC-I and WFPC2). Our sample includes the dense clusters M15, 47 Tuc, M30, NGC 6624, M3 and M13. The two main goals of our program are to measure the shape of stellar density profile in clusters (the slope of the density cusp in post core collapse clusters, in particular) and to understand the nature of evolved stellar populations in very dense regions and their variation as a function of radius. The latter includes studies of blue straggler stars and of the central depletion of bright red giants. Our recent WFPC2 study of M15 is described in detail.

We present preliminary results from an ongoing study of the central 5 arcmin2 of NGC 6624 based on short F336W, F439W, and F555W (UBV) Hubble Space Telescope WFPC2 exposures (Yanny et al. 1996). NGC 6624 is a dense, metal rich, post core collapse globular cluster at a distance of 8.1 kpc. Nearly 5000 stars with V ≳ 21 (1.5 mag below the turnoff) are detected within the 34′′ × 34′′ area of the PC1 CCD which imaged the cluster center. Individual stars brighter than V = 20 are easily identifiable in the central image section shown in Fig. 1. Image simulations and similar data on the denser cluster M15 indicate that the effects of incompleteness and photometric error are negligible on the V < 19.5 sample of stars in NGC 6624. The stellar surface density profile derived from such a sample is well approximated by a power law of index α = −0.85 (Fig. 2). The density profile shows no hint of flattening towards smaller radii in the radial range over which it is reliably measured (r ≳ 0′′.3). A B vs. U – V color-magnitude diagram of the r < 15′′ region (Fig. 3) shows a well defined blue straggler sequence. Our preliminary findings are consistent with an earlier study of this cluster by Sosin and King (1995) using pre-repair FOC images.

The high angular resolution of the Hubble Space Telescope will provide opportunities for many fundamental observations of globular clusters, most of which have been extensively discussed in the literature. We have therefore chosen to devote our time (and pages) to a presentation of what HST observations may reveal about some aspects of galactic globular clusters. To avoid infringing upon programs that others may propose, we have limited ourselves to simulations of observations that are part of our Guaranteed Time Observations. [The complete catalog of GTO observations has published by the Space Telescope Science Institute and is available upon request.]

The eclipsing binaries UW CMa, AO Cas, and V729 Cyg have been systems of great interest for over fifty years. The light curves are complex and suffer significant changes on a time scale of months, but the primary attraction of these systems is that both components have O-type spectra; thus they present us with some of the few possibilities for direct measurement of absolute dimensions of very massive stars. Much effort has been expended on these systems, but no really consistent model has emerged.