A three-component mass model of the Galaxy consisting of a modified exponential disk, a spherical inner bulge and a massive outer corona has been derived that attempts to give a valid description of observed features over a wide range of galactic distances. The new model shows the steep rise of the circular velocity close to the galactic centre with a first peak of the rotational velocity at approximatelyr=350 pc and a deep minimum aroundr=2 kpc. Outside the solar circle the rotation-velocity stays reasonably constant, requiring the addition of a massive dark corona. A third feature of this model is a variable disk-thickness like that of an equilibrium disk with constant velocity dispersion in thez-direction. A two-step procedure deriving the potential field has been used: First, a model consisting of a bulge, a massive corona and a disk of infinitesimal thickness has been fitted to rotation curve data, and the potential field was then computed using numerically performed Hankel-transforms. In a second step this field was then modified following Vandervoort's (1970a) procedure in order to make it to agree with the potential of a specified thick disk model. Both the Oort constantsA andB of the model agree with recent observed values, and the local mass density is identical to Oort's value ρ0=0.15M
⊙ pc−3. The same is true forK

 z
 in the solar neighbourhood. A discussion of Oort's curve forK

 z
 in the light of the evidence given by the model even results in an observed value of ρc=0.0019M
⊙ pc−3 for the local mass density of the corona compared to ρc
M
⊙ pc−3 in the model. If the model data are inserted into a relation given by the galactic warp theory by Bertin and Mark (1980), we find a good agreement with empirical data from Henderson (1979). The scale size of the disk can be checked by a comparison with the logarithmic density gradient of disk material as given by Blaauw (1965) and Oort (1960, 1965), and it is shown that the visual aspect of equilibrium disk models seen from the outside does not contradict the well-known appearence of edge-on spirals.

A realistic model of the galaxy

This review is devoted to studies of the Gould belt and the Local system. Since the Gould belt is the giant stellar-gas complex closest to the sun, its stellar component is characterized, along with the stellar associations and diffuse clusters, cold atomic and molecular gas, high-temperature coronal gas, and dust contained in it. Questions relating to the kinematic features of the Gould belt are discussed and the most interesting scenarios for its origin and evolution are examined.

The Gould Belt

Some statistical studies on the nearby early-type stars proposed for observations by HIPPARCOS are presented. Results on spatial orientation and kinematics are in agreement with those found in the literature. An age estimate based on non-kinematical hypothesis is found to be somewhat smaller than expansion ages derives by some authors.

The characteristics and origin of the Gould's Belt

We assemble principal constituents of the morphology of the Orion Arm within 1500 pc as a starting point for the study of progression of star formation.

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Star formation in the orion arm

The information contained in the local stellar velocity field is discussed. The local expansion, also reveiled by the interstellar gas, is interpreted in terms of a scenario where giant clouds are formed in galactic shocks, give birth to stars and subsequently expand.

A. Tsioumis

Papers

Galactic rotation and local irregularities derived from fundamental proper motions and radial velocities

A Contribution to the Kinematics of the Gould Belt