#include "erfa.h" int eraStarpv(double ra, double dec, double pmr, double pmd, double px, double rv, double pv[2][3]) /* ** - - - - - - - - - - ** e r a S t a r p v ** - - - - - - - - - - ** ** Convert star catalog coordinates to position+velocity vector. ** ** Given (Note 1): ** 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 (arcseconds) ** rv double radial velocity (km/s, positive = receding) ** ** Returned (Note 2): ** pv double[2][3] pv-vector (AU, AU/day) ** ** Returned (function value): ** int status: ** 0 = no warnings ** 1 = distance overridden (Note 6) ** 2 = excessive speed (Note 7) ** 4 = solution didn't converge (Note 8) ** else = binary logical OR of the above ** ** Notes: ** ** 1) The star data accepted 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 pv-vector is likely to be ** merely an intermediate result, so that a change of time unit ** would 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. ** ** 2) The resulting position and velocity pv-vector is with respect to ** the same frame and, like the catalog coordinates, is freed from ** the effects of secular aberration. Should the "coordinate ** direction", where the object was located at the catalog epoch, be ** required, it may be obtained by calculating the magnitude of the ** position vector pv[0][0-2] dividing by the speed of light in ** AU/day to give the light-time, and then multiplying the space ** velocity pv[1][0-2] by this light-time and adding the result to ** pv[0][0-2]. ** ** Summarizing, the pv-vector returned is for most stars almost ** identical to the result of applying the standard geometrical ** "space motion" transformation. The differences, which are the ** subject of the Stumpff paper referenced 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 RA proper motion is in terms of coordinate angle, not true ** angle. If the catalog uses arcseconds for both RA and Dec proper ** motions, the RA proper motion will need to be divided by cos(Dec) ** before use. ** ** 5) Straight-line motion at constant speed, in the inertial frame, ** is assumed. ** ** 6) An extremely small (or zero or negative) parallax is interpreted ** to mean that the object is on the "celestial sphere", the radius ** of which is an arbitrary (large) value (see the constant PXMIN). ** When the distance is overridden in this way, the status, ** initially zero, has 1 added to it. ** ** 7) If the space velocity is a significant fraction of c (see the ** constant VMAX), it is arbitrarily set to zero. When this action ** occurs, 2 is added to the status. ** ** 8) The relativistic adjustment involves an iterative calculation. ** If the process fails to converge within a set number (IMAX) of ** iterations, 4 is added to the status. ** ** 9) The inverse transformation is performed by the function ** eraPvstar. ** ** Called: ** eraS2pv spherical coordinates to pv-vector ** eraPm modulus of p-vector ** eraZp zero p-vector ** 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 ** eraPpp p-vector plus p-vector ** ** Reference: ** ** Stumpff, P., 1985, Astron.Astrophys. 144, 232-240. ** ** Copyright (C) 2013-2014, NumFOCUS Foundation. ** Derived, with permission, from the SOFA library. See notes at end of file. */ { /* Smallest allowed parallax */ static const double PXMIN = 1e-7; /* Largest allowed speed (fraction of c) */ static const double VMAX = 0.5; /* Maximum number of iterations for relativistic solution */ static const int IMAX = 100; int i, iwarn; double w, r, rd, rad, decd, v, x[3], usr[3], ust[3], vsr, vst, betst, betsr, bett, betr, dd, ddel, ur[3], ut[3], d = 0.0, del = 0.0, /* to prevent */ odd = 0.0, oddel = 0.0, /* compiler */ od = 0.0, odel = 0.0; /* warnings */ /* Distance (AU). */ if (px >= PXMIN) { w = px; iwarn = 0; } else { w = PXMIN; iwarn = 1; } r = ERFA_DR2AS / w; /* Radial velocity (AU/day). */ rd = ERFA_DAYSEC * rv * 1e3 / ERFA_DAU; /* Proper motion (radian/day). */ rad = pmr / ERFA_DJY; decd = pmd / ERFA_DJY; /* To pv-vector (AU,AU/day). */ eraS2pv(ra, dec, r, rad, decd, rd, pv); /* If excessive velocity, arbitrarily set it to zero. */ v = eraPm(pv[1]); if (v / ERFA_DC > VMAX) { eraZp(pv[1]); iwarn += 2; } /* Isolate the radial component of the velocity (AU/day). */ eraPn(pv[0], &w, x); vsr = eraPdp(x, pv[1]); eraSxp(vsr, x, usr); /* Isolate the transverse component of the velocity (AU/day). */ eraPmp(pv[1], usr, ust); vst = eraPm(ust); /* Special-relativity dimensionless parameters. */ betsr = vsr / ERFA_DC; betst = vst / ERFA_DC; /* Determine the inertial-to-observed relativistic correction terms. */ bett = betst; betr = betsr; for (i = 0; i < IMAX; i++) { d = 1.0 + betr; del = sqrt(1.0 - betr*betr - bett*bett) - 1.0; betr = d * betsr + del; bett = d * betst; if (i > 0) { dd = fabs(d - od); ddel = fabs(del - odel); if ((i > 1) && (dd >= odd) && (ddel >= oddel)) break; odd = dd; oddel = ddel; } od = d; odel = del; } if (i >= IMAX) iwarn += 4; /* Replace observed radial velocity with inertial value. */ w = (betsr != 0.0) ? d + del / betsr : 1.0; eraSxp(w, usr, ur); /* Replace observed tangential velocity with inertial value. */ eraSxp(d, ust, ut); /* Combine the two to obtain the inertial space velocity. */ eraPpp(ur, ut, pv[1]); /* Return the status. */ return iwarn; } /*---------------------------------------------------------------------- ** ** ** Copyright (C) 2013-2014, 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. 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