epochProp( tYr, astrom6 )
The input and output astrometry parameters are each represented by a 6-element array, with the following elements:
index gaia_source name unit description ----- ---------------- ---- ----------- 0: ra deg right ascension 1: dec deg declination 2: parallax mas parallax 3: pmra mas/yr proper motion in ra * cos(dec) 4: pmdec mas/yr proper motion in dec 5: radial_velocity km/s barycentric radial velocityThe units used by this function are the units used in the
gaia_source
table.
Null values for parallax
, pmra
,
pmdec
and radial_velocity
are treated as if zero for the purposes of propagation.
The documentation of the equivalent function in the Gaia archive
comments "This is a reasonable choice for most stars because
those quantities would be either small (parallax and proper motion)
or irrelevant (radial velocity).
However, this is not true for stars very close to the Sun,
where appropriate values need to be taken from the literature
(e.g. average velocity field in the solar neighbourhood)."
The effect is that the output represents the best estimates available for propagated astrometry; proper motions, parallax and RV are applied if present, but if not the output values are calculated or simply copied across as if those quantities were zero.
tYr
(floating point)astrom6
(array of floating point)t0+tYr
,
represented by a 6-element array as aboveepochProp(-15.5,
array(ra,dec,parallax,pmra,pmdec,radial_velocity))
- calculates the astrometry at 2000.0 of gaia_source values
that were observed at 2015.5double[] epochProp(double, double[])