Neutral gas in the inner few kpc of the Milky Way is notable for showing strong non-circular motions, large excursions from the nominal galactic plane, and an overwhelming preponderance of molecular (rather than atomic) neutral gas. Here, we discuss the coherent nature of the kpc-scale tilts seen in H I and CO emission and demonstrate the congruence of the inner-Galaxy atomic and molecular gas distributions, out more than 1 kpc in radius and 300 pc vertically from the center. We point out that features in inner-Galaxy spectra can usually not be identified with discrete, underlying material entities, but instead arise solely as the result of kinematic projection effects.

The galactic centre contains the largest concentration of molecular clouds in the Galaxy. The clouds in the central region are unusual in having large linewidths and masses, and large non-circular motions. Previous surveys of their distribution in the central region have been carried out in OH (Robinson & McGee 1970; Cohen & Few 1976), H2CO (Whiteoak & Gardner 1979; Cohen & Few 1981), CO (Bania 1977; Dame et al. 1987; Bally et al. 1987, 1988) and CS (Bally et al. 1987, 1988). The OH groundstate lines at 18cm wavelength have certain advantages for such a survey. The OH lines appear in absorption against the galactic centre continuum sources, and against the continuum emission from the disk of the Galaxy. The absorption spectra are sensitive to relatively small molecular column densities. In addition they can give information on the relative positions of the molecular gas and the radio continuum sources. This paper describes results from an absorption line survey of the galactic centre region in the OH main lines at 1667.359 MHz and 1665.402 MHz (Boyce & Cohen 1994).

In this review I discuss stars in the bulge of our Milky Way, but I exclude stars within a few parsec from Sgr A West; they are the subject of other reviews at this Symposium. We should, however, not forget that there may be an intimate connection between the central cluster and the bulge: bulge stars may eject matter that feeds the monster at the center and eruptions by this monster may have an important effect on the bulge.

One of the unsolved problems of the Milky Way is the interplay between the different components (disk, bulge and halo) in the inner regions, where they may all reach their maximum density. As a first approach to attack this problem, we summarize the results of a photometric and spectroscopic study of the Galactic bulge based on ∼700 K and M giants in 3 fields (Minniti 1993a). Table 1 lists the position of the fields, their projected Galactocentric distance, number of stars with spectra at present, and estimated disk contamination.

N-body simulations for stars in bar potentials have demonstrated over the last couple of years (e.g., Combes et al. 1990; Raha et al. 1991) that bars growing in z will lead to the presence of a bulge component. In such a scenario a central “bulge” component could develop as a resonance phenomenon caused by a bar and would be distinctly different from any “spheroidal” or “halo” component.

We surveyed 313 color-selected IRAS sources in the Bulge in the SiO J=1−0 (v=1, 2) lines with the Nobeyama 45m telescope, which resulted in 222 detections (Nakada et al. 1992; Izumiura et al. 1994ab). The detection rates exceeded 80% for the brighter samples (Table 1). We discuss the observed SiO maser characteristics and the implications of the obtained 1-v diagram.

Galactic H2O masers are associated either with the circumstellar shells of late-type stars or with star-forming regions (SFRs). Previous surveys for H2O masers had revealed relatively few near the Galactic Center (GC). We report on the continuation of a survey using the VLA to make 22.2 GHz observations of IRAS point sources which lie within 2° of the GC and which have either 12 μm or 25 μm flux > 8 Jy. Taylor, Morris and Schulman (TMS, 1992, AJ, 106, 1978) previously observed 97 of 342 candidate sources. We have observed 160 more and plan to complete the survey in early 1995.

An OH/IR star is an intermediate mass AGB star which loses mass and is optically obscured by its envelope. Such stars can be detected in the infrared and by radio maser lines. In particular the OH line (1612 MHz) is bright and has a distinctive profile, that allows us to determine the radial velocity of the central star. OH/IR stars are excellent tracers for the study of Galactic dynamics because they are bright, unaffected by extinction in the OH line – and therefore visible throughout the Galaxy – and because they represent a wide range of stellar masses. The outflow velocity of the circumstellar shell is most likely driven by radiation pressure from the central star on the dust. Therefore outflow velocity increases with stellar luminosity and metallicity, and decreases with age.

Near Infrared photometry (JHKL'M) of 78 SRVs in field #3 (PG3) of the Palomar Groningen Variable Star Survey (1 = 0°, b = −10°) was obtained at the ESO 1-m telescope, La Silla, Chile.

We explore a series expansion method to calculate the instabilities and the structure of the perturbations for a variety of uniformly rotating finite stellar disks. This survey focuses on the role of the distribution function in stability analyses. Although the potential does not show differential rotation, it will in many cases be a reasonable approximation for the disk in the central regions of galaxies without massive central mass concentration.

Using the Richardson-Lucy algorithm the two-integral distribution function (2I-DF) f(E,Lz ) for Kent's (1992) Bulge model has been constructed. It turns out to be negative (and hence unphysical) at Lz ≈ Lc. The physical reason for this result and its implications are discussed.

The history of the Galaxy is encoded in the kinematic, chemical and age profiles of its various populations, and their inter-relationships. Of these, the age structure has proved to be the most problematic. The aim of the present paper is to discuss our understanding of the ages of the various components and to seek to understand the chronology of the system, highlighting along the way some of the unsolved problems.

The paper of Eggen, Lynden-Bell and Sandage (1962)(hereafter ELS) titled “Evidence from the motion of old stars that the Galaxy collapsed” was the first attempt to understand the formation and evolution of our Galaxy. From a study of a kinematically selected sample of high velocity stars, ELS had found a remarkable correlation between chemical abundance and orbital eccentricity, in the sense that stars with the largest ultraviolet excess (a measure of stellar metallicity, in particular Fe), i.e. the lowest metallicity, are invariably moving in highly elliptical orbits. As the average < [Fe/H] > (in the usual notation [Fe/H] = log(Fe/H)∗ – log(Fe/H)⊙) is expected to increase with time, as a consequence of the progressive chemical enrichment of the gas, stars with the lowest [Fe/H] are, on average, the oldest. ELS also found a correlation between abundance and motion of stars perpendicular to the Galactic plane. This correlation suggests a continuous decrease of the perpendicular velocity with decreasing [Fe/H]. To explain these relations ELS proposed that the Galaxy collapsed from a protocloud to a thin disk on a timescale of a few times 108 years, with progressive chemical enrichment as the collapse proceeded. This model was subsequently criticized mainly because of selection effects in their data, i.e. given the data available to ELS one would not expect the sample to contain low abundance, low orbital eccentricity objects even if they existed. They would be absent from the high velocity catalog they used. In addition, the ELS simple model did not account for the fact that almost half of the halo stars have retrograde orbits. This fact led Larson (1969) to consider models of clumpy and turbulent protogalaxies with collapse times that sometimes exceeded 1 Gyr.

The radii of globular clusters are used to study the early evolution of the Galactic halo. It is found that such cluster radii increase with Galactocentric distance and depend on orbit shape. It is suggested that metal enrichment in the Galactic halo might have been mainly a local phenomenon, whereas cluster radii may have been determined by more global properties of the protogalaxy.

F-G dwarf stars of different metallicity are used as tracers of chemical and dynamical history of the Galaxy. Observed ratios of element abundances “[X/Fe] versus [Fe/H]” (where “X” is a some of chemical element) are compared with theoretical ones and allow us to make the choice between models (or parameters of theoretical models) of the Galaxy chemical evolution, nucleosynthesis and processes of star formation. Our experience has shown (Bikmaev, 1991, 1994a,b; Bikmaev et al., 1990) that in some cases classical approaches in abundance determination are affected by methodical uncertainties and the spread in [X/Fe] ratios may be large even if high quality spectra used.

The stellar metallicity distribution of low-mass stars is one of the major touchstones for models describing the chemical evolution of our Galaxy. In contrast to the gaseous components, the abundances of the stellar components also reflect the temporal enrichment. Hence, the stellar metallicity distribution is a stringent test for evolutionary models of galaxies.

It is reasonable to say that if Jan Oort were alive today, he would no doubt find recent developments in the study of the Galactic bulge to be fascinating. Oort considered the Galactic bulge in two contexts. First, he was interested in the use of the RR Lyrae stars as probes to determine the distance to the Galactic Center. No doubt, Oort would have been excited about the growing evidence of the bulge's triaxiality, as well as by the debate over the age of the bulge. His second interest was in the nature of activity at the center, an issue that I will not discuss in this review. The latter also remains an unsolved problem of the Milky Way, and (based on his work) one that might have been nearer to his heart than this one. Yet the question of when the bulge formed is ultimately a question about the formation history of the Galaxy. The oldest stars (those whose ages we are certain of) are found in Galactic globular clusters, the sum total of which are ≈ 5 × 107M⊙. The field population of the bulge is ≈ 2–3 × 1010M⊙, an order of magnitude more massive than the field population of the metal poor spheroid. So if the bulge formed all at once, and early, then the Milky Way had a luminous, even cataclysmic youth. But if the bulge formed later in the history of our galaxy, as a starburst or dynamical instability of the central disk, then the young Milky Way may have been inconspicuous and primeval galaxies may be hard to find indeed. If our bulge formed very early, its stellar population might have much in common with the giant ellipticals, while a late bulge might teach us much about processes that affect galaxy evolution.

Mira and non-Mira M stars are easily distinguished by means of their near-infrared colours. The Miras show a large range of mass-loss rates, and the actual rates are a strong function of the K-[12] colour. The kinematics and scale heights of these Miras are a function of their pulsation periods. The period distribution of Miras in the South Galactic Cap is similar to that of Miras in the Bulge. Non-Mira M stars in the South Galactic Cap have similar colours to their counterparts in the Bulge but differ from bright M-giants in the solar neighbourhood. The galactic distribution and scale height of the M giants is a function of colour and it is suggested that differences in composition influence the colours.

To study the way in which the principal periodic orbits in a Galactic potential determine orbital structure, horizontal and vertical surfaces of section, i.e. (dR/dt, R) and (dz/dt, z), are being used to explore the potential of Allen & Santillán (1991) and to investigate possible vertical structure in the Galactic halo. The chaotic “scattering” process due to the nearly spherical mass distribution close to the Galactic center in conjunction with the confinement of the chaotic orbits produces a vertical segregation of both chaotic and non-chaotic orbits in the halo. Certain z max , z min are preferred by the chaotic orbits over others as a result of the conservation of the total orbital energy and of the interaction and confinement of the chaotic orbits by the principal families of periodic orbits (Figure 1). Some of these periodic orbits have been identified. Correlations between the structure found in the observed W distribution and that of the numerically determined z max , z min histograms are shown for our sample of 280 halo stars (Schuster et al. 1993). W is the star's velocity perpendicular to the Galactic plane and z max , z min the maximum distances above or below the Galactic plane, respectively, reached by the star in the course of its orbit. This vertical structure may explain certain puzzling observations of the galactic halo, such as conflicting c/a values for the shape of the halo, and unusual velocity dispersions and/or distributions near the Galactic poles. These results are in good agreement with Hartwick's (1987) two component model for the halo.

We investigate the growth of the velocity dispersion in the initial stage of the cold dissipationless collapse of spherical collisionless systems by a perturbation theory. We show that the tangential velocity dispersion grows faster than the radial one for the system with centrally condensed initial density profile.