We present preliminary results from BVRI CCD photometry of stars in the galactic bulge. The importance of disc contamination is shown. Several statistical criteria to separate disc from bulge stars are used.

We present K-counts for a number of stars with K ≤ +9.0 in 3 clear regions near the galactic centre. They are located approximately at l∼0.0 and b ∼ −3.5, −4.0 and −4.5. Their Cumulative Counts Functions (CCF's) are formed, and with the aid of an exponential disc model for the Galaxy are separated into disc and bulge CCF. As for the case in Baade's Window (BW) (Ruelas-Mayorga and Teague, 1992a) the disc is dominant at bright magnitudes whereas the bulge dominates at fainter ones. The slope of the bulge CCF is steeper than that for the disc in all cases corroborating the result obtained for BW. The two colour JHK and the K vs J-K diagrams show that the stellar population in these areas is similar to that studied in BW by us and by Frogel and Whitford (1987). An average E(J-K) ∼0.42 mag for the reddening is obtained. At K ≤ +9.0, the disc may be accounted for by those sources with J-K ≤ +1.6 whereas the bulge population presents values for J-K in excess of +1.6.

The results of a new method, Post Theoretical Mass Method (PTM) are presented in order to investigate radial pulsating stars (RPS) in galaxies. Further implications for stellar and galactic astrophysics are also discussed.

We derive the heavy element abundances for hundreds of K-giants in seven windows of low extinction, along or near the minor axis of the Galactic bulge. By using the recently-calibrated Washington photometric filter system, the distribution function in [Fe/H] is determined for each field. Within 8° of the Galactic center (∼ 1 kpc) our data are consistent with no gradient in the distribution of [Fe/H], which may hint to a dissipationless collapse, and/or sufficient mixing during the star-forming epoch when Fe was produced in the bulge. The mean abundance over this region is between two and five times solar. The form of these distributions is well-fitted by the simple (closed box) model of chemical evolution where the bulge is self-enriched by processing its original gas content to completion. Beyond 8° from the Galactic center, our data show that the mean of the abundance distributions drops precipitously. This is consistent with the notion that the inner bulge is chemically distinct from the halo.

An analysis of the differential ultraviolet extinction towards four bulge planetary nebulae, based on the observed line ratio of He II 1640/4686Å, shows that the ultraviolet reddening law towards the bulge is much steeper than in the solar neighbourhood. An analysis of the optical reddening law for 42 bulge PN, based upon observed Balmer line ratios and Hβ to radio free-free flux ratios, is presented. The optical reddening law towards the bulge is steeper than in the local ISM, and thus the ratio of total to selective extinction, Rv = 2.29 (± 0.50), is lower than the standard solar neighbourhood value of Rv = 3.10.

We present abundance determinations, in particular C/H and C/O ratios, for 11 Galactic bulge PN, based on spectrophotometry in the UV from IUE and in the optical from the Anglo-Australian Telescope. The derived abundances are compared with values for PN in the Galactic disk. The mean C/O ratio for bulge PN is significantly lower than that found for Galactic disk PNs. Additionally we present an abundance analysis of the very metal-poor halo population PN M2-29, which is located in the bulge.

The 135 OH/IR stars within 0.8 deg (∼ 100 pc) of the Galactic Center (GC) identified in a search with the VLA (Lindqvist et al. 1991) are in rapid rotation about the center with a regression line showing a velocity gradient of 1.2±0.1 km s−1, equivalent to 178 km s—1 deg−1 for Ro = 8.5 kpc (Lindqvist et al. 1992). This is of the same order as the inward extrapolation of the Galactic rotation curve derived from the terminal velocities of HI for l < 2 deg (Burton and Gordon 1978) and the general trend of the velocities of the CO clouds in the equatorial disk mapped by Dame et al. (1987) (Fig. 1b). These OH/IR stars are located along the ridge of highest projected CO density. This spatial location and the flat configuration argue for assignment to the disk population, a possibility suggested by Feast (1989). The VLA objects are not in general supergiants (Blommaert et al. 1992). On a K-band map of an area 1×2 deg around the GC, Catchpole et al. (1990) found a number of stars brighter than (mK)o = 5. On the assumption that BCK = 3.3, (Frogel and Whitford 1987), and Ro = 8.5 kpc, Mbol < — 6.3, i.e., in the supergiant range.

Using the VLA at 1612 MHz Lindqvist et al. (1992a) have found 134 OH/IR stars close to the Galactic Centre (GC). These stars plus 15 from Habing et al. (1983) have been used as probes of the gravitational potential to derive the mass distribution in the inner galactic bulge between ≈ 5 to ≈ 100 pc from the GC (Lindqvist et al., 1992b). In this paper we present a progress report of a dynamical model which we have applied to the data.

A grid of synthetic spectral energy distributions, representative of old stellar populations, has been used to derive colors in different photometric systems, and to compare the theoretical predictions with observational data for galactic globular clusters.

The aim of the project is to investigate the role of different horizontal branch morphologies on the integrated light of globular clusters.

We explore the proper motion distributions of anisotropic Plummer models, and show that information on the orbital structure can be obtained, even if no distance information is available.

The present state of the Galaxy can be idealized as a stellar system with several components: inner bulge, main bulge, thin disk, thick disk, stellar halo, corona, etc. In the regions where the diffusion phenomena are negligible, the dynamics can be determined from a conservative dynamic system, according to the superposition principle with a common potential. Here we describe the kinematical behavior of the main bulge, thin and thick disks, and stellar halo, depending on the cylindrical galactocentric coordinates r and z, under axisymmetric conditions. The angular dependence is treated in the work by Sanz-Subirana & Juan-Zornoza (1992).

The main purpose in this work is to present some analytical results about the spatial distribution of the stars in the Galactic Bulge. These results have been obtained by considering that the stellar system verifies the collisionless Boltzman equation and the ellipsoidal hypothesis (non-axisymmetrical) for the distribution of peculiar velocities of the stars.

It is not always clear what the bulge of the Galaxy is: a region close to the centre, a subsystem formed by a distinct population, or a mixture of populations but characterised by its own mass distribution. We consider the bulge of the Milky Way as a subsystem and thus contributing to the galactic gravitation field. We want to estimate the contribution of the galactic bulge to the rotation curve.

We present a set of axisymmetric Stäckel potentials which can be used for Galactic dynamical modelling. Each of them has a halo–disk structure with a flat rotation curve.

We present a new method for finding a distribution function f, which depends only on the two classical integrals of energy E and angular momentum J about the axis of symmetry, for a stellar system with a known axisymmetric potential and density.

We present global dynamical models for bulge–disk systems. The phase–space structure is examined by means of two integral models. The models indicate that in the formation merger argument for ellipticals one cannot always assume that the maximum phase–space density occurs in the center of the system.

We present a simple axisymmetric model with an elementary distribution function capable of representing galactic bulges. The gravity field of the galaxy is based on the axisymmetric logarithmic potential, which has a flat rotation curve. Bulges are built as isothermal distributions of stars embedded within the potential.

The study of prevalent orbits in galactic subsystems can help us understand galactic structure and clarify its history. The classical analysis of flat orbits and metallicities of old stars led Eggen et al. (1962) to formulate the rapid collapse of the primordial Galaxy. On the other side Yoshii & Saio (1979) studied three-dimensional orbits that separate in spherical coordinates. They found the Galaxy contracted quasi-stationary after the formation of halo objects. Here we shall briefly discuss the results of numerical orbit calculations (with Merson's method) for selected galactic subsystems. The axially symmetrical two-component model of the Galaxy (Kutuzov, Ossipkov 1989) was adopted. One-component models (Barkhatova et al. 1987, Kutuzov 1988) were used also but no significant difference in orbit elements was found (Kutuzov & Ossipkov 1992). Pericenter and apocenter distances, Rp and Ra , and the maximal height of objects over the galactic plane, zm , were used as orbit elements as well as dimensionless quantities e = (Ra — Rp )/(Ra + Rp ) (eccentricity) and c = 2zm /(Ra — Rp ) (the flatness of box filled by orbit projection on the meridional plane).