Jean-Paul Colin

Photometric Monitoring of the Lensed QSO 0957+561

We present our first results of a photometric monitoring project of the twin quasar 0957+561. This project aims mainly at the improvement of the determination of the time delay ΔT(A,B) for this gravitational lens, since the “time delay controversy on QSO 0957+561 (is) not yet decided” (Pelt et al. 1994). In addition, the quite large field of the CCD used allows also a long-term astrometric and photometric study of stars and galaxies in the field within a radius of about 10 arcminutes around the lens.

The Status of Absolute Proper Motions and the Kinematics of Globular Clusters

We have studied a sample of 26 globular clusters for which so far absolute proper motions exists in the literature. The proper motions were combined with distances and radial velocities for a determination of the space motion of the clusters. Using different galactic potentials (see Dauphole & Colin 1994 and references therein we calculated the orbits of the globular clusters and thier time averaged eecentricities, total energies, and apo- and perigalactic distances. The relation of the orbital quantities to the metalicities of the globular clusters has been studied. Preliminary results of this study were presented in Geffert et al. (1993).

Are there Two Populations of Subdwarf B Stars Visible in Kinematic Samples

The discussions about stellar populations and their spatial distribution can be best advanced by studies of special and well defined star types. The study of subdwarf B stars provides great promise: it is relatively easy both to find sdB stars and to determine their physical parameters.