We have obtained new photometric and spectroscopic data for a large sample of cool white dwarfs. These data have been analysed with state-of-the-art model atmospheres and effective temperatures and atmospheric compositions have been determined (Bergeron, Ruiz & Leggett 1997). Radii and masses have also been obtained for those stars with accurate parallax measurements. These high quality data and models allow us to produce an improved cool white dwarf luminosity function based on the Liebert, Dahn & Monet (1988) proper motion sample. The turn-over seen at the faint end of this luminosity function, combined with theoretical cooling sequences, enable us to constrain the age of the local region of the Galaxy.

The maximum age of galactic globular clusters provides the best observational constraint on the minimum age of the Universe. One of the main “missing link” in the globular cluster age determination has been the lack of a precise calibration, with local subdwarfs, of the position of the subdwarf sequence at different [Fe/H].

Hipparcos data may change this situation. As many precise parallaxes become available for local subdwarfs, the distance to globular clusters can be estimated directly from ZAMS fitting to the subdwarf locus. The ages can then be inferred from the turnoff luminosity (a robust prediction of stellar evolution models), rather than using secondary indicators such as Horizontal-Branch position, or indicators depending on the uncertain colour scale such as turnoff colour.

Combining Hipparcos parallaxes with [Fe/H] values determined with the CORAVEL spectrometer, we are studying the position of the subdwarfs in the Colour-Magnitude Diagram from a sample of more than 900 subdwarf candidates. Preliminary results are presented here. It is shown that the distances of many subdwarfs had been underestimated in previous studies, mainly because a large fraction of them is in fact evolved off the main sequence into the turnoff or the subgiant branch.

Since the early 1970's, the consensus “best estimate” of the age of the Galactic globular cluster (GC) system has been 15–16 ±3 Gyr. However, a number of recent studies, which are briefly reviewed herein, have suggested that this estimate is too high by ≳ 15%. Based on a consideration of new stellar models and the latest developments concerning the cluster distance scale, the present paper lends support to the notion that the first globulars began to form in the Galaxy 13–14 Gyr ago. In addition, our analysis of absolute GC ages adds to the mounting evidence that the dispersion in age among clusters having similar metallicities is probably quite small. As a consequence, age can hardly be the primary factor causing the wide diversity in their horizontal-branch morphologies.

The scientific study of the topic of this Symposium, “Fundamental Stellar Properties,” was in its infancy at the turn of the Century. As illustrated at this meeting, there has been significant progress in many directions over the past 100 years. Despite this progress, there are however many unsolved problems that will be addressed by theoretical and observational techniques that are emerging only now.