A complete census of the stellar populations in galaxies must include not only the Main Sequence and various post-Main Sequence populations (SGB, RGB, AGB, HB, plus degenerate objects such as WD and NS) but also the pre-Main Sequence (PMS) stellar population.

In the solar neighbourhood, we can assume that a stellar sample is composed of two stellar populations: thin disk and thick disk stars. If we assume as the only hypothesis that each stellar component is associated with a Schwarzchild velocity distribution function (e.g., Sanz, J., Juan, J.M., this symposium), then it is possible to determine the velocity distribution of both components (Cubarsi, R.: 1990, AJ 99, 1558). Thus, starting from the central velocity moments up to fourth order of the overall stellar sample we obtain the partial moments, the difference between centroid velocities and the percentage of mixture. Moreover, a set of 25 constraint equations between the total moments is determined. This method has been applied to some local stellar samples under the hypothesis of a two-component mixture (Hernandez-Pajares, M.: 1991, this symposium) and the obtained kinematical features of the stellar components are in agreement with kinematical properties of thin disk and thick disk stars described from other physical viewpoints (e.g., Sandage, A.: 1987, in The Galaxy, eds. G. Gilmore, R.F. Carswell (Reidel), p. 321).

The group of known X-ray sources associated with a Be star in a binary system consists of about 40 objects. They are the most abundant type of massive X-ray binary in the Galaxy. In this contribution we present an up-to-date picture of the main physical characteristics of these objects, including their evolutionary history, mass transfer mechanism, an interpretation of their behaviour in the orbital versus spin period diagram and the use of Be/X-ray sources as galactic tracers.

Based on a new sample of (IRAS based) OH/IR stars (te Lintel Hekkert et al., 1991, A&AS, in press), and a catalogue of planetary nebulae compiled by Acker (1983, A&AS, 54, 315), we show the relation between these two groups of objects, in terms of the kinematics and the Galactic distribution. In contrast with earlier analyses of samples of OH/IR stars, we find a close correlation between the kinematics of the planetary nebulae and the IRAS based sample of OH/IR stars. In particular, we find that the distribution of the planetary nebulae (PN) shows a good correlation with the OH/IR stars which have a low outflow velocity (vexp < 12.5 km s–1). Whether the high outflow velocity OH/IR stars also have a counterpart among PN is not clear.

In this paper we explore the hypothesis that the blue progenitor of SN 1987A was a component of a close binary. It is shown that a blue spectral appearance at the end of core helium burning (and possibly also during the following evolutionary phases) is a natural phenomenon for a star with initial mass between 9 M⊙ and 15 M⊙ which was originally in a close binary with mass ratio q ≍ 1 and who accreted at least 8 – 10 M⊙ while already being a hydrogen shell burning star. This phenomenon does not depend on the exact treatment of the convective core overshooting, the stellar wind mass loss rate, and the metallicity. A blue SN progenitor in the Galaxy would therefore be a surprise.

A grid of 200 synthetic spectra was built in the wavelength region λλ 478-530 nm, and a method was developed for deriving the stellar parameters temperature, gravity and metallicity from low-resolution stellar spectra. The parameters of the observed spectra are derived by dividing the observed spectrum by that of a reference star. The resulting δf(λ) = log F*/Fref is then used, in conjunction with the grid of synthetic spectra, to derive the final parameters, through a perturbation method. The method was applied to a sample of 41 stars in the Basel field SA 141 (1 = 245°, b = −85.8°). Since this direction points closely to the south galactic pole, the binning of stars into appropriate distance intervals provides a coarse view of the metallicity distributions associated with the major galactic populations: we find the thin disk, thick disk and halo components near the current best estimates of their scale heights above the galactic plane. The first results were presented in Cayrel et al. (1991a, A&A, 247, 108; 1991b, A&A, 247, 122). Further observations are in progress, with the aim of having a sample of about 1000 stars.

Recently Maccagni et al. (ApJ, 334, L1, 1989) obtained g, r and i images of an X-ray luminous galaxy at the center of a poor cluster of galaxies (1E1111.9-3754). The images showed that the central galaxy was surrounded by a remarkable spatially extended red envelope, visible as a kink in the r14 surface brightness profile at a radius of 100 kpc. Johnstone & Fabian (MNRAS, 237, 27p, 1989) suggested that the red envelope is composed of low mass stars formed in a cooling flow. This observation sparked considerable interest as the first direct detection of low mass star formation in cooling flows. We have obtained near infrared H-band (1.65 μ images of 1E1111.9-3754 from the Infrared Imaging Spectrometer on the 4-m Anglo-Australian Telescope. Even though low mass stars should be more prominent in the near infrared than at optical wavelengths, the 1.65 μ surface brightness profile shows no deviation from the r14 profile out to a radius of 100 kpc. This observation argues against the hypothesis that the envelope is composed of low mass stars formed from cooled X-ray gas.

Our knowledge of the distribution of low mass stars (T-associations) in the Galaxy, as an indicator of star forming regions (SFR), is badly known due to an observational bias. A correlation with high-mass stars (OB-associations) will not solve the problem, because some well known SFR as Taurus and Chamaleonis seem to preferentially form low mass stars. One way to tackle this question is by invoking the distribution of known T Tauri stars (TTS) and the distribution of selected IRAS sources that are potential candidates to be new TTS. We must be aware, however, that an important number of TTS are not IRAS sources. Considering these distributions, we have found a smooth distribution of SFR along the local galactic plane. The number of TTS in each SFR is very variable probably due to a variable efficiency of star formation. Also there are some isolated TTS from SFR which could indicate the dissipation of old SFR or that some TTS can be formed from isolated very small clouds.