The catalogue is intended to aid all those who engaged in linking of reference frames by means of radio stars, and in the maintenance of the links. Accordingly, it also addresses observers who provide in future observations of stars at optical and radio wavelengths. To this end we structured the catalogue by categories that are divided into three main groups of data: astrometric quantities including double and multiple stars, astrophysical quantities, and ancillary quantities giving references to finding charts, radio maps, radio emission and interferometer networks.
With regard to the star designation we tried to cover a wide range of names to simplify the identification of objects. As far as the other categories are concerned it was our aim to make primarily one single entry that reflects the optimum quantity of this category. Clearly, the choice was not always unambiguous, a fact which led occasionally to several entries. Since only those data appear in the catalogue that are published in the literature and have received a quotation, the term "optimum'' should be seen in this context. Especially the astrometric entries suffer from the restriction to quotable data, because many of them are still in the pipeline and their publication is tied to the finalization of the respective projects, such as the Hipparcos data reduction or campaigns of radio interferometry. To enable the conscientious catalogue user of taking avantage of data whose publication is imminent, we have given ample star identifications in the name list, for instance the Hipparcos star number, and references to the interferometer networks dealing with one or other of the stars. Hence, cross-referencing to any sort of data is made easy. In addition, the bibliographical codes associated with each entry facilitate the deepening of data retrieval.
Transformations of positions and proper motions from B1950.0 to J2000.0 were performed along the lines of Aoki et al. (1983) and Schwan (1988). The catalogue is an extract from a comprehensive data base of radio stars maintained at the Astronomisches Rechen-Institut, which in addition keeps on file a machine-readable catalogue version.
Per star a maximum of 18 categories of stellar parameters were entered in the
catalogue, each category consisting of one or more records and accompanying
references. Throughout the catalogue a uniform system of units was applied.
The detailed definition of the categories and adopted units will be found in
the catalogue header.
Category 1: Star designations are listed in 3 columns of 20
characters each per entry. If available, the following six designations are
arranged in hierarchical order: (1) A 4-digit working number precedes
the customary designations to permit easy cross-referencing to the reservoir
of radio stars by Walter et al. (1990), (2) Durchmusterungs-number (BD, CoD,
CPD), (3) HD number, (4) PPM number, (5) Hipparcos Input Catalogue number
(HIC), (6) variable star designation; (7) and so on reserved for other
designations in alphabetical order.
Category 2: Optical position: Right ascension (RA) and standard
deviation, declination (Dec) and standard deviation, referred to J2000.0 at
observation epoch; observation epochs in RA and Dec; the reference system of
positions (usually the FK5 system). Normally the parallax effect is
removed from the coordinates. For certainty, consultation of the
reference is suggested.
Category 3: Radio positions: RA and standard deviation, Dec and standard
deviation, referred to J2000.0 at observation epoch; observation epochs in RA
and Dec; the reference system of the calibrators. Concerning the
parallax effect see Category 2.
Category 4: Optical proper motions in RA and Dec referred to J2000.0; the
reference system of proper motions (usually the FK5 system).
Category 5: Radio proper motions in RA and Dec referred to J2000.0; the
reference system of the calibrators.
Table 1: Catalogue entries of star 1028 = BD+280532 = HD 21242 =
PPM 92507 = HIC 16042
Category 6: Optical parallax.
Category 7: Radio parallax.
Category 8: Radial velocities.
Category 9: Apparent magnitude of the star and the respective photometric
system (U, B, V, R, P, H (Hipparcos), K (Kukarkin)). For variable
stars normally maximum and minimum values of magnitude, and the period are
quoted. For double and multiple systems, occasionally, the integrated magnitude
is given supplemented by the magnitudes of the components.
Category 10: Type of variability.
Category 11: Spectral type and luminosity class of star or system. If
available, the respective quantities of the components are listed too.
Category 12: Optical structure.
Category 13: Properties of double stars: Type of binary or multiple
system, number of components, separation of components,
position angles, magnitudes.
Category 14: Guide to finding charts.
Category 15: Guide to radio maps.
Category 16: Guide to radio emission.
Category 17: Observation priority, membership to observing
programmes.
Category 18: Miscellaneous (X-ray source, emission line star, star
association, etc.).
Whenever a category is void it has been omitted from the records of the respective star.
The bibliographical codes accompanying the entries are compiled at the end of the catalogue under the heading "References''. The list of references is arranged both in order of ascending bibliographical codes and in alphabetical order of the authors' names.
For exemplification we present in Table 1 the sample of the entries of star 1028 = BD+280532 = HD 21242 = PPM 92507 = HIC 16042. The catalogue as a whole is available at the CDS.
