Durchmusterung

In astronomy, Durchmusterung or Bonner Durchmusterung (BD), is the usual name for three comprehensive astrometric star catalogues of the whole sky, processed by the Bonn Observatory (Germany) from 1859 to 1903.^[1] Today, the term Durchmusterung includes not only stars but also the search for other celestial objects. Special tasks are the celestial scanning in electromagnetic wavelengths which are shorter or longer than visible light waves. The name comes from Durchmusterung ("run-through examination"), a German word used for a systematic survey of objects or data.

Original

The 44 years work of the Bonner Durchmusterung (abbreviated by BD) tabulates the positions and apparent magnitudes of approximately 325,000 stars to apparent magnitude 9–10. It was the basis for an excellent star atlas^[2] (some 100 pages) and for the AGK and SAO catalogues of the 20th century. The BD star numbers are still used and allow the correlation of this pioneering work with modern projects.

The format of a BD number is exemplified by BD-16 1591 which is the BD number of Sirius. The -16 component is the declination of Sirius, and 1591 a leaping number.^[3]

Extension

Many astronomical projects — from studies of celestial mechanics and the solar system, up to the nascent field of astrophysics — were essentially supported by Atlas and data of the Bonner Durchmusterung. But some decades later the positional accuracy began to be insufficient for more exact projects. Further the BD could not cover the whole sky, because far southern stars are not visible from Germany.

So the scientific community decided to supplement the Southern Sky by two additional astrometric surveys which should be carried out by observatories located at the Southern hemisphere: Córdoba, Argentina, and Cape Town, South Africa. The Cordoba Durchmusterung (abbreviated CD, or, less commonly, CoD) was made visually — similar to the former BD), but the Cape Photographic Durchmusterung (CPD) was conducted by the new photographic technique, which just before was shown to have sufficient accuracy. Similar to the BD numbers, the southern stars are identified by CD and CPD numbers.

To establish a more exact reference system for the Bonner Durchmusterung, in the late 19th century the astronomers and geodesists began to work on a Celestial Fundamental Co-ordinate System, based on the Earth's rotation axis, the vernal equinox and the Ecliptic plane. This astrometric project led to the Fundamental Catalogue of the Berlin observatory and was used as an exact coordinate frame for the BD and AGK. It was modernized in the 1920s (FK3, mean accuracy ±1"), up to the present FK6 as the latest step of cosmic geodesy (accuracy 0.1"). Together with radioastronomical measurements the FK6 accuracy is now better than ±0.1".

Modern counterparts

The most important development has been the Hipparcos satellite, operated between 1989-93, which observed around 118,000 stars over the whole sky, and led to three very accurate star catalogues:

• Hipparcos Catalogue (118,000 stars, average accuracy ±0.001")
• Tycho Catalogue (about 1,050,000 stars, with accuracy ±0.03"), and
• Tycho-2 Catalogue (about 2,500,000 stars) which was improved for double star effects and proper motions using the Astrographic Catalogue observations.

In the next decade a further step is planned using a future satellite, Gaia. The Gaia catalogue plans to include around one billion stars, with an apparent magnitude limit of around 20. Therefore, it will include a sufficient number of stars of our galaxy to assist future projects of modern space science with greater accuracy and wider sample size.

References

1. ^ Bonner Durchmusterung at VizieR Service, Centre de Données astronomiques de Strasbourg
2. ^ Kanas, Nick (2007). Star maps: history, artistry, and cartography. Berlin: Springer. pp. 302–304. doi:10.1007/978-0-387-71669-5. ISBN 978-0-387-71668-8. http://www.springerlink.com/content/978-0-387-71668-8. 
3. ^ BD query at Simbad database, Centre de Données astronomiques de Strasbourg

Further reading

• Lectures on Stellar Statistics. Charlier. 1921