An IR-scan of the Baade's Window () area (BW) has been obtained (Ruelas-Mayorga etal., 1983). The Cumulative Counts Function (CCF) at 2.2 μm (No. of sources per sq. degree down to a given K magnitude) down to K ≃ +13.5 was formed by combining 1.9-m telescope scans with Anglo Australian Telescope (AAT) scans.

OH/IR stars are the infrared counterparts of galactic OH maser sources which show a characteristic double-peaked emission-line profile. Their strong radio emission can be detected at large distances, making them excellent tracers of distribution and kinematics of evolved stars in the Milky Way. The OH maser profile is typical for line emission from an expanding circumstellar shell. The circumstellar shells of OH/IR stars absorb the optical emission of the central star nearly completely and reemit the energy in the infrared. Having luminosities ~ 105 L⊙ and energy distributions peaking around 10μm, they may make a major contribution to the interstellar radiation field beyond 5μm. With mass loss rates of 10-5 to 10-4 M⊙/yr they lose several solar masses in a few hundred thousand years. OH/IR stars are therefore important objects for recycling stellar matter into the interstellar medium.

Progress has been made in understanding the nature of OH/IR stars. They are Mira-like large-amplitude variables with periods up to 5 years long. It is proposed that they are stars of intermediate mass (2–10 M⊙) on the asymptotic giant branch (AGB). They have not only larger masses than Mira variables proper, but also longer periods of pulsation and larger mass loss rates. As a result optically thick circumstellar dust shells are formed, which prevent the detection of these more massive Mira-like variables at optical wavelengths. Radial pulsation (Mira variability) is thus thought to occur for all intermediate-mass stars in the course of their evolution on the AGB. In view of their high mass-loss rates, these stars may be key objects in the study of the formation of planetary nebulae.

The distribution of the stellar disk component is studied with particular emphasis on the properties of open clusters. A scale height of 80 pc is found for clusters younger than 109 years while the scale height is 200 pc for older clusters. A radial metallicity gradient in the disk is confirmed but there seem to be significant abundance variations apart from this. There are radial gradients in age as well as in linear diameter. Kinematically, there are a number of regions in the Milky Way with systematic radial velocity residuals.

The third edition of the computer-based catalogue of open-cluster data has now been produced and is disseminated through the Centre de Données Stellaires, 11 rue de l'Université, F-67000 Strasbourg, France. It is also available through World Data Center A, NASA, Greenbelt, MD 20771, USA.

The concept of star streams originally due to Kapteyn is revived. It is suggested that the existence of Stream II may have been overlooked, yet it is of crucial importance in specifying the true local standard of rest.

The kinematical study of the stars in the solar neighbourhood allows, via the equation of the so-called asymmetrical drift, to deduce the sum of the gradients of the density and the velocity dispersions, . In order to deduce the density gradients in the solar neighbourhood, the second term is generally supposed to be zero. This kind of hypothesis, certainly wrong, comes from the old “ellipsoidal theory”. A velocity dispersion independent of is not compatible with the Toomre's local stability. On the contrary, if we suppose negligible value compared with ∂1n (Mayor, 1974). Using Vandervoort's (1975) hydrodynamical approach, Erickson (1975) obtains a similar value for the local velocity-dispersion gradient.

Using the Walraven VBLUW photometric system, we have studied the metal content of 89 F and G stars in the Galactic South Pole field SA141. Our sample is based on the Basel survey of RGU photometry in Selected Areas, and it contains all stars in SA141 with VJ <14m.5 and (G-R)<1m.15 (spectral types earlier than about G7). The observations were made with the VBLUW photometer and the 90-cm Dutch Telescope at ESO, La Silla.

For unreddened intermediate-type stars the VBLUW photometry enables us to separate the effects of temperature, gravity, and metallicity (cf. Lub and Pel, 1977). Since reddening is negligible in SA141, we can therefore determine these three parameters for each program star once the photometric indices are calibrated in terms of Teff, log g, and [Fe/H]. The latter calibration was made in a semi-empirical way, using VBLUW observations of stars with spectroscopic analyses in combination with theoretical colors based on the model spectra by Kurucz (1979). We used the Hyades main-sequence as a zeropoint, adopting [Fe/H] = +0.15 for this cluster.

The results in the (V-B)-(B-L) diagram are shown in Fig. 1. This diagram is very sensitive to metallicity, but almost gravity-independent. Fig. 1 indicates that most program stars have metallicities in the range −1 ≦ [Fe/H] ≦ 0. The distribution of the program stars in the gravity-sensitive (V-B)-(L-U) diagram is very narrow, log g =4.2 ± 0.3, which means that these stars are probably all dwarfs, with only very few possible subgiants.

The absolute-magnitude calibration was derived by using the data of Cayrel de Strobel et al. (1980) and of Cayrel de Strobel and Bentolila (1983). From their [Fe/H]-catalogue we took all stars with known distances, and within the parameter range of our program stars, to construct an empirical MV - Teff relation. This relation was used to derive distances for the stars in SA141.

These distances are plotted against [Fe/H] in Fig. 2. The diagram clearly shows the correlation between distance and metallicity, suggesting for this particular sample a gradient of −0.6 in [Fe/H] over the first 500 pc. Similar values were found in the Basel RGU program (cf. Trefzger, 1981) and by Blaauw and Garmany (1975).

The approach by Bahcall and Soneira to the determination of galactic parameters through the use of star counts is referred to, and tests of the Bahcall-Soneira Galaxy model based on additional observational data are discussed.

The determination of the local mass density by Hill, Hilditch and Barnes through studies of A and F stars in the region of the North Galactic Pole is briefly discussed, as is a recent investigation of the problem by Bahcall.

In the determination of the galactic force Kz and the local mass density from the density distribution ν(z) and the distribution f(W) of velocities at right angles to the galactic plane for a group of tracer stars, it is important to secure homogeneity of the tracer group. This has led Hill, Hilditch and Barnes in a continuation of their investigation to use photoelectric uvby photometry to segregate homogeneous groups of F stars. A similar approach is followed by Danish astronomers, whose work is briefly described.

Our Galaxy is the only galaxy in which the 3-dimensional distribution of visible mass, chemical abundances and the stellar velocity field are all directly measurable. A project to determine these properties is currently underway, utilising direct photographic plates from the UK Schmidt telescope and the Las Campanas du Pont reflector, and the COSMOS and APM automated measuring machines. These provide reliable number-magnitude-colour distributions for complete samples of stars to V = 19 in 20 square degrees, and V = 22 in 1 square degree, in each of eight directions. These data may then be directly interpreted to determine the density profile, shape and luminosity function of the Galactic spheroid.

We report progress on a spectroscopic and photometric programme devoted to the study of the dynamics of O-F5 stars within 15° of the North and South Galactic Poles. The aims of the programme are to test dynamical and chemical evolution models of the Galaxy by establishing velocity dispersions as a function of z-distance for stars of different population groups. We are also able to investigate the interstellar reddening at the poles and the kinematic properties of apparently normal early-type stars found more than 1 kpc from the galactic plane.

We are currently engaged in astrometry of Kapteyn Selected Area photographic plates covering the period 1908 to the present day using the GALAXY measuring engine at RGO. Our intention is to use the apparent motions to investigate the stellar velocity structure within a kiloparsec of the Sun. We have completed a preliminary analysis of SA 68 (ℓ = 1110, b = 460), deriving positions and proper motions using the central overlap method on measures of plates spanning the period 1909 to 1980. These include the original (1909) and second epoch (1925) plates taken with the Radcliffe refractor at Oxford, and used in the compilation of the Radcliffe Catalogue (Knox-Shaw and Scott-Barrett, 1934), as well as more recent plates taken using the 26-inch refractor at Herstmonceux. For stars present on all thirteen exposures (including double exposures on the same plate) the internal residuals in positions in each co-ordinate are per plate, giving annual motions accurate to ~1 milli-arcsecond over the 71 year baseline. Since our plates have a limiting magnitude of only B ~15, we have used 17 stars in common with Chiu (1980) to transform our relative motions to the absolute frame. Our motions are in very good agreement with those by Chiu, with a scatter of less than 3 milliarcseconds in each co-ordinate and linearity of scale between the two datasets.

Unfortunately, the text of this review paper is not available. For recent reviews, we refer the reader to the following papers:

We have used the NRAO 140-ft telescope to survey galactic HI near the galactic equator. The observations cover the part of the sky north of δ = −40° in the latitude range b = −20° to at least +20°; in some regions the survey extends to b = +33°. The longitude coverage in the equator ranges from ℓ = 340° to 270°. The data represent an improvement over existing large-scale HI surveys in terms of velocity coverage (±250 km s−3), velocity resolution (1 km s−1), sensitivity (3σ = 0.2 K), and extent of sky coverage, but not in density (δℓ × δb = 1° × 1°) of coverage.

We have measured the vertical distribution of HI in the first quadrant of galactic longitude between tangent-point radii, Rt = Ro sin ℓ, of 2.5 kpc and 9.75 kpc at 250 pc intervals of tangent-point distance, using the 305m Arecibo telescope and the 91m and 43m NRAO telescopes. The survey is complete to at least z = ±500 pc and it was sampled with half-beamwidth spacings; the angular resolutions at 21cm wavelength are 4, 11 and 20 arcmin for these instruments.

This investigation presents a total picture of the well-known corrugation-phenomenon for the (heliocentric) longitude range 10° ≤ 1 ≤ 240° as derived from HI-studies. For each spiral arm of the spiral pattern of Simonson (1976), we derived the centroid of the HI distribution from the 21-cm line surveys of Weaver and Williams (1974), Sinha (1979), and Westerhout and Wendlandt (1982). The three-component mass model of Rohlfs and Kreitschmann (1981) was used to derive a radial-velocity field, which was supplemented by a radial expansion field and by density-wave kinematics. This combined field served to calculated kinematic distances. The warp was taken into account according to Henderson et al. (1982) and Kulkarni et al. (1982).

In their analysis of global properties of the Galaxy based on the HI distribution outside of the solar circle, Knapp, Tremaine, and Gunn (1978 - hereafter referred to as KTG) have examined the extreme HI velocities for the outer edge of the Galaxy. They fit these values to a model based on an exponential drop-off of HI surface density with galactocentric radius, R, and a flat rotation curve. Adopting a value of 4 kpc for the scale length, L, of this drop-off, KTG fit the extreme velocities with various values of θo (the circular rotation speed of the Local Standard of Rest), to obtain a best fit of θo − 220 km/s. While KTG obtained sensitive observations with the NRAO 43-m radio telescope for the galactic-longitude range 1 = 80° to 225°, they had to rely on the HI survey by Kerr, Harten, and Ball (1976 - hereafter referred to as KHB), obtained with the Australian 64-m radio telescope at Parkes, for the balance of the Southern Milky Way.

Pulsars provide probably the best probes of electron density in the plane of the Galaxy. The dispersion measure, the path integral of electron density along the line of sight from the pulsar to Earth, ∫ neds, is directly measurable from multi-frequency pulse-timing observations. The distance to a pulsar, d, can be estimated from its HI absorption and emission spectra. The mean electron density along the line of sight is then just <ne> = ∫ neds/d.

Observations of the large-scale distribution of molecular clouds in external galaxies offer a unique opportunity for investigating galactic evolution. New generations of stars form in these dense regions, and the most massive of these stars recycle their processed interiors into the interstellar medium. Early observations of the CO distribution in the Milky Way (Scoville and Solomon 1975; Burton and Gordon 1976) indicated that there is intense emission at the center of our Galaxy, very little gas between 1 and 4 kpc radius, and a “molecular ring” feature between 4 and 8 kpc. Observations of molecular clouds in external galaxies of a variety of Hubble types and luminosities will enable us to more clearly understand the origin of this distribution. Although no other galaxies are observed to contain CO distributions precisely like that in the Milky Way, the differences which are present provide important clues to the structure and evolution of galaxies.

Young and Scoville (1982) have argued that the CO distribution, and by inference the H2 distribution, follows the shape of the blue luminosity of the disk, and is thus exponential. However, full maps of bright-CO galaxies (Rickard and Palmer 1981) show considerable structure, with real peaks and depressions on scales as small as the telescope beam. This means that the noise in the determination of the underlying structure is dominated not by the instrumental contribution but by the intrinsic noise of the structure itself. A correct analysis of the axisymmetric structure requires the use of statistical tests comparing the observations with different hypothetical distributions. One finds that equally good fits can be obtained with exponential distributions, r-1 distributions, or even flat disks with central nuclei. However, profiles of the full map data averaged over azimuth, with “error” bars determined by the structural variation with azimuth, show a clear deviation from the optical luminosity profile in the outer disk of NGC 6946. Furthermore, if the profiles for NGC 6946 and IC 342 are fit with exponentials, the scale lengths are rather larger than previously suggested (8.9 and 6.6 kpc, respectively). By sampling only a few radii, one can miss much of the emission of the outer parts of the galaxies, and also underestimate the intrinsic noise of the structure.

We present results (partly preliminary) of an extensive map (73 positions) of CO (J=1–0) emission in M51 (Fig. 1). The spectra were obtained with the Onsala 20-m antenna (beam size 33″), equipped with a cooled mixer and a 512×1 MHz multichannel receiver. The data are not yet fully analyzed but our preliminary results are as follows:

1. A small central minimum in the CO emission is apparent (Fig. 2). The average radial CO distribution shows a maximum at ~ 15″ (corresponding to 0.7 kpc, for an assumed distance of 9.6 Mpc).

2. The above minimum results from what seems to be an oval ridge structure in the emission intensity around the center, with an extent of about 30″ by 40″ (Fig. 3). This could be the markings of an elongated hole or the beginning of the spiral arms. (The ridges are fairly well correlated with the innermost parts of the spiral arms as delineated by continuum observations by Segalowitz, 1976.)

3. It seems that a central oval velocity pattern is needed to explain a dip at 450 km s-1 in the central spectrum. (The dip is present in all and independent parts of our data.)

4. The outer parts of the galaxy have only been covered in strips (Fig. 1). Clearly there is structure in these strips, i.e. not only a radial decrease. The “on-arm” spectrum (88″, 0″) has for example a greater integrated and peak intensity than the “interarm” spectrum (77″, 0″). Such arm-interarm contrast is not always clear, though. Observations covering a larger section of an arm-interarm region, where contrast has been seen, are being planned for the next observing season.

5. We also note that the observed apparent velocity differences between CO and ionized gas, reported by Rydbeck et al. (1983), persist. A fully convincing argument on this point (taking into account the finite beam etc.) requires some further model work, however.