| 1 | #include "slalib.h"
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| 2 | #include "slamac.h"
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| 3 | float slaRvgalc ( float r2000, float d2000 )
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| 4 | /*
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| 5 | ** - - - - - - - - - -
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| 6 | ** s l a R v g a l c
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| 7 | ** - - - - - - - - - -
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| 8 | **
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| 9 | ** Velocity component in a given direction due to the rotation
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| 10 | ** of the Galaxy.
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| 11 | **
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| 12 | ** (single precision)
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| 13 | **
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| 14 | ** Given:
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| 15 | ** r2000,d2000 float J2000.0 mean RA,Dec (radians)
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| 16 | **
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| 17 | ** Result:
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| 18 | ** Component of dynamical LSR motion in direction r2000,d2000 (km/s)
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| 19 | **
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| 20 | ** Sign convention:
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| 21 | ** The result is +ve when the dynamical LSR is receding from the
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| 22 | ** given point on the sky.
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| 23 | **
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| 24 | ** Called:
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| 25 | ** slaCs2c, slaVdv
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| 26 | **
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| 27 | ** Note: The Local Standard of Rest used here is a point in the
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| 28 | ** vicinity of the Sun which is in a circular orbit around
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| 29 | ** the Galactic centre. Sometimes called the "dynamical" LSR,
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| 30 | ** it is not to be confused with a "kinematical" LSR, which
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| 31 | ** is the mean standard of rest of star catalogues or stellar
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| 32 | ** populations.
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| 33 | **
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| 34 | ** Reference: The orbital speed of 220 km/s used here comes from
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| 35 | ** Kerr & Lynden-Bell (1986), MNRAS, 221, p1023.
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| 36 | **
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| 37 | ** Last revision: 23 March 1994
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| 38 | **
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| 39 | ** Copyright P.T.Wallace. All rights reserved.
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| 40 | */
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| 41 | {
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| 42 | /*
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| 43 | **
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| 44 | ** LSR velocity due to Galactic rotation
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| 45 | **
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| 46 | ** Speed = 220 km/s
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| 47 | **
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| 48 | ** Apex = L2,B2 90deg, 0deg
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| 49 | ** = RA,Dec 21 12 01.1 +48 19 47 J2000.0
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| 50 | **
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| 51 | ** This is expressed in the form of a J2000.0 x,y,z vector:
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| 52 | **
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| 53 | ** va(1) = x = -speed*cos(ra)*cos(dec)
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| 54 | ** va(2) = y = -speed*sin(ra)*cos(dec)
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| 55 | ** va(3) = z = -speed*sin(dec)
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| 56 | */
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| 57 | static float va[3] = { -108.70408f, 97.86251f, -164.33610f };
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| 58 | float vb[3];
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| 59 |
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| 60 | /* Convert given J2000 RA,dec to x,y,z */
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| 61 | slaCs2c ( r2000, d2000, vb );
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| 62 |
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| 63 | /* Compute dot product with LSR motion vector */
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| 64 | return slaVdv ( va, vb );
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| 65 | }
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