GLACTC_PM
Name
GLACTC_PM
Purpose
Convert between celestial and Galactic (or Supergalactic) proper
motion (also converts coordinates).
Explanation
Program to convert proper motion in equatorial coordinates (ra,dec)
to proper motion in Galactic coordinates (gl, gb) or Supergalacic
Coordinates (sgl,sgb) or back to equatorial coordinates (j=2).
The proper motion unit is arbitrary, but be sure to set /MUSTAR if
units are the projection of the proper motion on the RA, Dec axis.
It does precession on the coordinates but does not
take care of precession of the proper motions which is usually a
very small effect.
Calling Sequence
GLACTC_PM, ra, dec, mu_ra,mu_dec,year, gl, gb, mu_gl, mu_gb, j,
[ /DEGREE, /FK4, /SuperGalactic, /mustar ]
Input Parameters
year equinox of ra and dec, scalar (input)
j direction of conversion (input)
1: ra,dec,mu_ra,mu_dec --> gl,gb,mu_gl,mu_gb
2: gl,gb,mu_gl,mu_gb --> ra,dec,mu_ra,mu_dec
INPUTS OR OUTPUT PARAMETERS: ( depending on argument J )
ra Right ascension, hours (or degrees if /DEGREES is set),
scalar or vector.
dec Declination, degrees,scalar or vector
mu_ra right ascension proper motion any proper motion unit
(angle/time)
mu_dec declination proper motion in any proper motion unit
(angle/time)
gl Galactic longitude, degrees, scalar or vector
gb Galactic latitude, degrees, scalar or vector
mu_gl galactic longitude proper motion in any time unit
mu_gb galactic latitude proper motion in any time unit
All results forced double precision floating.
Optional Input Keyword Parameters
/DEGREE - If set, then the RA parameter (both input and output) is
given in degrees rather than hours.
/FK4 - If set, then the celestial (RA, Dec) coordinates are assumed
to be input/output in the FK4 system. By default, coordinates
are assumed to be in the FK5 system. For B1950 coordinates,
set the /FK4 keyword *and* set the year to 1950.
/SuperGalactic - If set, the GLACTC returns SuperGalactic coordinates
as defined by deVaucouleurs et al. (1976) to account for the
local supercluster. The North pole in SuperGalactic coordinates
has Galactic coordinates l = 47.47, b = 6.32, and the origin is
at Galactic coordinates l = 137.37, b= 0
/mustar - if set then input and output of mu_ra and mu_dec are the
projections of mu in the ra or dec direction rather than
the d(ra)/dt or d(mu)/dt. So mu_ra becomes mu_ra*cos(dec)
and mu_gl becomes mu_gl*cos(gb).
Examples
Find the SuperGalactic proper motion of M33 given its
equatorial proper motion mu* =(-29.3, 45.2) microas/yr.
Where the (*) indicates ra component is actual mu_ra*cos(dec)
(Position: RA (J2000): 01 33 50.9, Dec (J2000): 30 39 36.8)
IDL> glactc_pm, ten(1,33,50.9),ten(30,39,36.8),-29.3,45.2, 2000,$
sgl,sgb,mu_sgl,mu_sgb,1,/Supergalactic,/mustar
==> SGL = 328.46732 deg, SGB = -0.089896901 deg,
mu_sgl = 33.732 muas/yr, mu_gb = 41.996 muas/yr.
And for the roundtrip:
IDL> glactc_pm, ra,dec,mu_ra,mu_dec,2000,$
IDL> sgl,sgb,mu_sgl,mu_sgb,2,/Supergalactic,/mustar
==> ra=1.5641376 hrs., dec= 30.660277 deg,
mu_ra= -29.300000 muas/yr, mu_dec=i 45.200000 muas/yr
Procedure Calls
BPRECESS, JPRECESS, PRECESS
History
Written Ed Shaya, U of MD, Oct 2009.
Adapted from GLACTC to make proper motion transformations,
Correct occasional sign error in galactic longitude E. Shaya Nov 2011