FK6
The FK6 , full title Sixth Catalog of Fundamental Stars (sixth catalog of fundamental stars ), is the latest fundamental catalog for the current decade and the basis for a stellar reference system high precision ( fundamental system of astronomy ). It represents a detailed database with coordinates and speeds of thousands of stars and is an optimal synthesis of satellite data with terrestrial measurements and its predecessor system FK5 .
The internationally used German abbreviation "FK" for F undamental- K atalog is continued in analogy to the FK3 and FK4 , which were created under the leadership of German astronomers and mathematicians between around 1920 and 1963. The first FK was published in 1907 as an appendix to the Berlin Astronomical Yearbook .
Development and content
The FK6 was published in 1999/2000 by the Astronomical Computing Institute (ARI) in Heidelberg and replaces the FK5, the accuracy of which it significantly exceeds. The reasons for this are:
- Combination with the astrological words of the astrometric satellite Hipparcos (1989-93), which have a high precision, but quickly become out of date due to the proper movement of the stars (see below)
- sharper criteria for star selection and grouping according to brightness and accuracy
- Elimination of suspected binary stars whose orbits would blur the precision.
Beyond 2010, the FK6 will define the heavenly (Zälestic) coordinate system. For astronomy and geodesy it serves as the most precise possible realization of a reference system for the coordinates right ascension and declination . The FK6 system with the underlying constants also represents a precise dynamic model of the planetary system and a quasi- inertial system for physics and extragalactic astronomy .
The FK6 contains fewer, but more accurate stars than its predecessor, the FK5. If it had 1535 fundamental stars (with an average accuracy of 0.04 ″ ) and 3117 supplement stars, there are now 878 + 3272 stars that are measured with an accuracy of better than ± 0.01 ″. For the time of the Hipparcos mission, the star locations are even 10 times more accurate, but become increasingly inaccurate due to their own movements (four years of measurement time were too short for the equivalent recording). The terrestrial measurements from 200 years make a significant contribution here, although they are less accurate.
The approximately 4150 stars of the FK6 are distinguished on the one hand by their publication (FK6 (1) and FK6 (3) according to the 1st and 3rd volume of the publication), on the other hand according to their "origin" (FK4, FK5 and FK5sup), because the Determining star velocities in terms of the coordinate system is an extremely tricky thing. If a star has been measured for precise star catalogs for 150 years , its changes are known much more reliably than with an FK3sup or FK4sup , which only came onto the watch lists around 1930 or 1960.
The exact number of 4150 stars depends on the current state of knowledge with regard to possible double stars, which are only included in an FK if more precise modeling is possible.
Newly developed quality models
A novelty of the FK6 is the additional classification according to star brightness and "astrometric quality":
The apparent brightness of the FK6 (1) stars ranges from 2 mag (like that of the Pole Star ) to about 6 mag (barely visible to the naked eye under good conditions). For the purposes of astrometry and the dynamics of the Milky Way, however, it is essential to also include a larger number of weaker (mostly more distant) suns.
Therefore, of the 3117 stars that were already included in the FK5, 992 were combined into the bright extension (BX) and 2125 into the faint extension (FX). The remaining 995 stars were subjected to different procedures. Together with other stars that were not sharply measured up to the year 2000, they form a measurement program for the next few years and decades.
Of all these precisely measured stars, about 50 percent were singled out as astrometrically excellent stars (340 + 1688 240). Your Hipparcos data are completely linear (within ± 0.0005 ″) over its 4-year measurement period. If this is not the case, there is the possibility of an as yet undetected double star whose orbital ellipses would blur the coordinates. The high accuracy of the FK6 system would no longer be guaranteed for the next 10–20 years.
Extrapolation into the future
According to the epoch for which an astronomer needs the star coordinates for his reductions or other research projects, the new system offers different speed models for star calculation since around 1930:
- Single star mode ( single star mode , SI)
- short-term prediction mode ( short-term prediction mode , STP), and
- long-term prediction mode ( long term prediction mode , LTP).
The reason is as follows: if star measurements from the time of Hipparcos have to be evaluated (which often happens when new asteroids , comets or novas are measured on older photo plates), the satellite measurements are more reliable. For models reaching into the present or the future, however, the older terrestrial measurements (with meridian circles or astrolabe ) should be given more weight, because otherwise the proper movements (lateral speed components of the stars) would not be optimally taken into account.
Without these mathematical-physical subtleties z. B. the "extension" ( extrapolation ) of the Hipparcos measurements in the future only 0.0022 ″ per year exactly. A suitable mix between STP and LTP, on the other hand, reduces the mean errors to 0.0005 ″ per year, the typical errors of a "simple" extrapolation.
In addition to these two to three classifications and three movement models, the FK6 contains further studies on special, distant double stars, the nature of which can be better assessed. In spite of predominantly geometric methods, modern astrometry intervenes deeply in astrophysics , which, conversely, also enriches directional measurements with its methods and spectral analyzes.
The actual fundamental system of the FK6 is linked to that of the predecessor FK5, but with sensible "stiffening" by the scanner method of the Hipparcos. The entire visual system of directions and rotations is in turn "anchored" to around 250 quasars , which can be measured with radio waves and interference methods much more precisely than would ever be possible in visual light . Similar methods of the VLBI are also used in earth measurements and plate tectonics .
The measurements of the Gaia mission completely change the data basis for star positions, both in the number of objects measured and in the size of the remaining measurement errors. The final Gaia catalog should have residual uncertainties depending on magnitude and spectral class between 25 µas for bright objects and about 300 µas for very weak objects.
history
| Short name | Number of stars | title | Published | Measurement places | Measurement of own movements | Overlap |
|---|---|---|---|---|---|---|
| Auwers, A., 1879 | 539 | Fundamental catalog for zone observations on the Nördl. sky | 1879 | Ø 1860 | ≈1850-1870 | up to dec. = −10 ° Note 1 |
| Peters, J., 1907 | 925 | New FK Berliner Astr. Yearbook based on the principles of Auwers | 1907 | Ø 1880 | 1745-1900 | up to dec. = −89 ° |
| FK3 | 873 | Third fundamental catalog of the Berlin Astronomical Yearbook | 1937 | 1912-1915 | from here over the whole sky, with epochs 1900, 1950, 2000 |
|
| FK3sup | 662 | (Additional stars, Volume II) | 1938 | Ø 1913 | 1845-1930 | |
| FK4 | 1,535 | Fourth Fundamental Catalog | 1963 | Ø 1950 | ||
| FK4sup | 1,111 | Supplement Stars FK4 / 5 | ≈1965 | |||
| FK5 | 1,535 | Fifth Fundamental Catalog | 1988 | Ø 1975 | ||
| FK5sup | 3.117 | Supplement Stars of FK5 | 1991 | |||
| Hipp. Note 2 | 118,000 | Hipparcos catalog | 1998 | 1989-1993 | 1989-1993 | |
| FK6 | 4,150 | Sixth Catalog of Fundamental Stars | 1999, 2000 | Ø 1992 |
Web links
- FK6 at the Astronomical Computing Institute Heidelberg
- Description at VizieR