diff options
Diffstat (limited to 'ast/erfa/pvstar.c')
| -rw-r--r-- | ast/erfa/pvstar.c | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/ast/erfa/pvstar.c b/ast/erfa/pvstar.c new file mode 100644 index 0000000..3a4e00b --- /dev/null +++ b/ast/erfa/pvstar.c @@ -0,0 +1,216 @@ +#include "erfa.h" + +int eraPvstar(double pv[2][3], double *ra, double *dec, + double *pmr, double *pmd, double *px, double *rv) +/* +** - - - - - - - - - - +** e r a P v s t a r +** - - - - - - - - - - +** +** Convert star position+velocity vector to catalog coordinates. +** +** Given (Note 1): +** pv double[2][3] pv-vector (AU, AU/day) +** +** Returned (Note 2): +** ra double right ascension (radians) +** dec double declination (radians) +** pmr double RA proper motion (radians/year) +** pmd double Dec proper motion (radians/year) +** px double parallax (arcsec) +** rv double radial velocity (km/s, positive = receding) +** +** Returned (function value): +** int status: +** 0 = OK +** -1 = superluminal speed (Note 5) +** -2 = null position vector +** +** Notes: +** +** 1) The specified pv-vector is the coordinate direction (and its rate +** of change) for the date at which the light leaving the star +** reached the solar-system barycenter. +** +** 2) The star data returned by this function are "observables" for an +** imaginary observer at the solar-system barycenter. Proper motion +** and radial velocity are, strictly, in terms of barycentric +** coordinate time, TCB. For most practical applications, it is +** permissible to neglect the distinction between TCB and ordinary +** "proper" time on Earth (TT/TAI). The result will, as a rule, be +** limited by the intrinsic accuracy of the proper-motion and +** radial-velocity data; moreover, the supplied pv-vector is likely +** to be merely an intermediate result (for example generated by the +** function eraStarpv), so that a change of time unit will cancel +** out overall. +** +** In accordance with normal star-catalog conventions, the object's +** right ascension and declination are freed from the effects of +** secular aberration. The frame, which is aligned to the catalog +** equator and equinox, is Lorentzian and centered on the SSB. +** +** Summarizing, the specified pv-vector is for most stars almost +** identical to the result of applying the standard geometrical +** "space motion" transformation to the catalog data. The +** differences, which are the subject of the Stumpff paper cited +** below, are: +** +** (i) In stars with significant radial velocity and proper motion, +** the constantly changing light-time distorts the apparent proper +** motion. Note that this is a classical, not a relativistic, +** effect. +** +** (ii) The transformation complies with special relativity. +** +** 3) Care is needed with units. The star coordinates are in radians +** and the proper motions in radians per Julian year, but the +** parallax is in arcseconds; the radial velocity is in km/s, but +** the pv-vector result is in AU and AU/day. +** +** 4) The proper motions are the rate of change of the right ascension +** and declination at the catalog epoch and are in radians per Julian +** year. The RA proper motion is in terms of coordinate angle, not +** true angle, and will thus be numerically larger at high +** declinations. +** +** 5) Straight-line motion at constant speed in the inertial frame is +** assumed. If the speed is greater than or equal to the speed of +** light, the function aborts with an error status. +** +** 6) The inverse transformation is performed by the function eraStarpv. +** +** Called: +** eraPn decompose p-vector into modulus and direction +** eraPdp scalar product of two p-vectors +** eraSxp multiply p-vector by scalar +** eraPmp p-vector minus p-vector +** eraPm modulus of p-vector +** eraPpp p-vector plus p-vector +** eraPv2s pv-vector to spherical +** eraAnp normalize angle into range 0 to 2pi +** +** Reference: +** +** Stumpff, P., 1985, Astron.Astrophys. 144, 232-240. +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double r, x[3], vr, ur[3], vt, ut[3], bett, betr, d, w, del, + usr[3], ust[3], a, rad, decd, rd; + + +/* Isolate the radial component of the velocity (AU/day, inertial). */ + eraPn(pv[0], &r, x); + vr = eraPdp(x, pv[1]); + eraSxp(vr, x, ur); + +/* Isolate the transverse component of the velocity (AU/day, inertial). */ + eraPmp(pv[1], ur, ut); + vt = eraPm(ut); + +/* Special-relativity dimensionless parameters. */ + bett = vt / ERFA_DC; + betr = vr / ERFA_DC; + +/* The inertial-to-observed correction terms. */ + d = 1.0 + betr; + w = 1.0 - betr*betr - bett*bett; + if (d == 0.0 || w < 0) return -1; + del = sqrt(w) - 1.0; + +/* Apply relativistic correction factor to radial velocity component. */ + w = (betr != 0) ? (betr - del) / (betr * d) : 1.0; + eraSxp(w, ur, usr); + +/* Apply relativistic correction factor to tangential velocity */ +/* component. */ + eraSxp(1.0/d, ut, ust); + +/* Combine the two to obtain the observed velocity vector (AU/day). */ + eraPpp(usr, ust, pv[1]); + +/* Cartesian to spherical. */ + eraPv2s(pv, &a, dec, &r, &rad, &decd, &rd); + if (r == 0.0) return -2; + +/* Return RA in range 0 to 2pi. */ + *ra = eraAnp(a); + +/* Return proper motions in radians per year. */ + *pmr = rad * ERFA_DJY; + *pmd = decd * ERFA_DJY; + +/* Return parallax in arcsec. */ + *px = ERFA_DR2AS / r; + +/* Return radial velocity in km/s. */ + *rv = 1e-3 * rd * ERFA_DAU / ERFA_DAYSEC; + +/* OK status. */ + return 0; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** All rights reserved. +** +** This library is derived, with permission, from the International +** Astronomical Union's "Standards of Fundamental Astronomy" library, +** available from http://www.iausofa.org. +** +** The ERFA version is intended to retain identical functionality to +** the SOFA library, but made distinct through different function and +** file names, as set out in the SOFA license conditions. The SOFA +** original has a role as a reference standard for the IAU and IERS, +** and consequently redistribution is permitted only in its unaltered +** state. The ERFA version is not subject to this restriction and +** therefore can be included in distributions which do not support the +** concept of "read only" software. +** +** Although the intent is to replicate the SOFA API (other than +** replacement of prefix names) and results (with the exception of +** bugs; any that are discovered will be fixed), SOFA is not +** responsible for any errors found in this version of the library. +** +** If you wish to acknowledge the SOFA heritage, please acknowledge +** that you are using a library derived from SOFA, rather than SOFA +** itself. +** +** +** TERMS AND CONDITIONS +** +** Redistribution and use in source and binary forms, with or without +** modification, are permitted provided that the following conditions +** are met: +** +** 1 Redistributions of source code must retain the above copyright +** notice, this list of conditions and the following disclaimer. +** +** 2 Redistributions in binary form must reproduce the above copyright +** notice, this list of conditions and the following disclaimer in +** the documentation and/or other materials provided with the +** distribution. +** +** 3 Neither the name of the Standards Of Fundamental Astronomy Board, +** the International Astronomical Union nor the names of its +** contributors may be used to endorse or promote products derived +** from this software without specific prior written permission. +** +** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS +** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE +** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, +** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, +** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; +** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER +** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN +** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +** POSSIBILITY OF SUCH DAMAGE. +** +*/ |