r year) rather than in km/sec or equivalent. Similarly, the typical absence of reliable radial velocities means that the transverse space motion (when known) is, in any case, only a component of the complete, three-dimensional, space velocity.
|• coincidence with ICRS (3 axes)||±0.6 mas|
|• deviation from inertial (3 axes)||±0.25 mas/yr|
|Number of entries||118,218|
|• with associated astrometry||117,955|
|• with associated photometry||118,204|
|Mean sky density||≈3 per sq deg|
|Limiting magnitude||V≈12.4 mag|
|Number of entries||1,058,332|
|• based on Tycho data||1,052,031|
|• with only Hipparcos data||6301|
|Mean sky density||25 per sq deg|
|Limiting magnitude||V≈11.5 mag|
|Completeness to 90 per cent||V≈10.5 mag|
|Completeness to 99.9 per cent||V≈10.0 mag|
|Tycho 2 Catalogue:|
|Number of entries||2,539,913|
|Mean sky density:|
|• at b=0°||≈150 per sq deg|
|• at b=±30°||≈50 per sq deg|
|• at b=±90°||≈25 per sq deg|
|Completeness to 90 per cent||V≈11.5 mag|
|Completeness to 99 per cent||V≈11.0 mag|
The final Hipparcos Catalogue was the result of the critical comparison and merging of the two (NDAC and FAST consortia) analyses, and contains 118,218 entries (stars or multiple stars), corresponding to an average of some three stars per square degree over the entire sky. Median precision of the five astrometric parameters (Hp<9 mag) exceeded the original mission goals, and are between 0.6–1.0 mas. Some 20,000 distances were determined to better than 10%, and 50,000 to better than 20%. The inferred ratio of external to standard errors is ≈1.0–1.2, and estimated systematic errors are below 0.1 mas. The number of solved or suspected double or multiple stars is 23,882. Photometric observations yielded multi-epoch photometry with a mean number of 110 observations per star, and a median photometric precision (Hp<9 mag) of 0.0015 mag, with 11,597 entries were identified as variable or possibly-variable.
For the star mapper results, the data analysis was carried out by the Tycho Data Analysis Consortium (TDAC). The Tycho Catalogue comprises more than one million stars with 20–30 milliarc-sec astrometry and two-colour (B and V band) photometry.
A more extensive analysis of the star mapper (Tycho) data extracted additional faint stars from the data stream. Combined with old photographic plate observations made several decades earlier as part of the Astrographic Catalogue programme, the Tycho-2 Catalogue of more than 2.5 million stars (and fully superseding the original Tycho Catalogue) was published in 2000.
The Hipparcos and Tycho-1 Catalogues were used to create the Millennium Star Atlas: an all-sky atlas of one million stars to visual magnitude 11. Some 10,000 nonstellar objects are also included to complement the catalogue data.
Between 1997 and 2007, investigations into subtle effects in the satellite attitude and instrument calibration continued. A number of effects in the data that had not been fully accounted for were studied, such as scan-phase discontinuities and micrometeoroid-induced attitude jumps. A re-reduction of the associated steps of the analysis was eventually undertaken. This has led to improved astrometric accuracies for stars brighter than Hp=9.0 mag, reaching a factor of about three for the brightest stars (Hp<4.5 mag), while also underlining the conclusion that the Hipparcos Catalogue as originally published is generally reliable within the quoted accuracies.
All catalogue data are available online from the Centre de Données astronomiques de Strasbourg.
The Hipparcos results have affected a very broad range of astronomical research, which can be classified into three major themes:
(a) the provision of an accurate reference frame: this has allowed the consistent and rigorous re-reduction of historical astrometric measurements, including those from Schmidt plates, meridian circles, the 100-year old Astrographic Catalogue, and 150 years of Earth-orientation measurements. These, in turn, have yielded a dense reference framework with high-accuracy, long-term proper motions (the Tycho-2 Catalogue). Reduction of cur