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diff --git a/math/slalib/doc/fk45z.hlp b/math/slalib/doc/fk45z.hlp new file mode 100644 index 00000000..6994302f --- /dev/null +++ b/math/slalib/doc/fk45z.hlp @@ -0,0 +1,83 @@ +.help fk45z Jun99 "Slalib Package" +.nf + + SUBROUTINE slF45Z (R1950,D1950,BEPOCH,R2000,D2000) + + - - - - - - + F 4 5 Z + - - - - - - + + Convert B1950.0 FK4 star data to J2000.0 FK5 assuming zero + proper motion in the FK5 frame (double precision) + + This routine converts stars from the old, Bessel-Newcomb, FK4 + system to the new, IAU 1976, FK5, Fricke system, in such a + way that the FK5 proper motion is zero. Because such a star + has, in general, a non-zero proper motion in the FK4 system, + the routine requires the epoch at which the position in the + FK4 system was determined. + + The method is from Appendix 2 of Ref 1, but using the constants + of Ref 4. + + Given: + R1950,D1950 dp B1950.0 FK4 RA,Dec at epoch (rad) + BEPOCH dp Besselian epoch (e.g. 1979.3D0) + + Returned: + R2000,D2000 dp J2000.0 FK5 RA,Dec (rad) + + Notes: + + 1) The epoch BEPOCH is strictly speaking Besselian, but + if a Julian epoch is supplied the result will be + affected only to a negligible extent. + + 2) Conversion from Besselian epoch 1950.0 to Julian epoch + 2000.0 only is provided for. Conversions involving other + epochs will require use of the appropriate precession, + proper motion, and E-terms routines before and/or + after FK45Z is called. + + 3) In the FK4 catalogue the proper motions of stars within + 10 degrees of the poles do not embody the differential + E-term effect and should, strictly speaking, be handled + in a different manner from stars outside these regions. + However, given the general lack of homogeneity of the star + data available for routine astrometry, the difficulties of + handling positions that may have been determined from + astrometric fields spanning the polar and non-polar regions, + the likelihood that the differential E-terms effect was not + taken into account when allowing for proper motion in past + astrometry, and the undesirability of a discontinuity in + the algorithm, the decision has been made in this routine to + include the effect of differential E-terms on the proper + motions for all stars, whether polar or not. At epoch 2000, + and measuring on the sky rather than in terms of dRA, the + errors resulting from this simplification are less than + 1 milliarcsecond in position and 1 milliarcsecond per + century in proper motion. + + References: + + 1 Aoki,S., et al, 1983. Astron.Astrophys., 128, 263. + + 2 Smith, C.A. et al, 1989. "The transformation of astrometric + catalog systems to the equinox J2000.0". Astron.J. 97, 265. + + 3 Yallop, B.D. et al, 1989. "Transformation of mean star places + from FK4 B1950.0 to FK5 J2000.0 using matrices in 6-space". + Astron.J. 97, 274. + + 4 Seidelmann, P.K. (ed), 1992. "Explanatory Supplement to + the Astronomical Almanac", ISBN 0-935702-68-7. + + Called: slDS2C, slEPJ, slEB2D, slDC2S, slDA2P + + P.T.Wallace Starlink 21 September 1998 + + Copyright (C) 1998 Rutherford Appleton Laboratory + Copyright (C) 1995 Association of Universities for Research in Astronomy Inc. + +.fi +.endhelp |