IRACpm R Package: Applies a 7-8 order distortion correction to IRAC astrometric data from the Spitzer Space Telescope and includes a function for measuring apparent proper motions between different Epochs.
#Instructions for installation into R
install.packages("devtools")
library(devtools)
install_github("esplint/IRACpm")
#Basic work flow:
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Read in files containing output from the Spitzer Science Center’s APEX single frame module form MOPEX using read.in.data.
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Measure image central world coordinates and rotations with CD.solver, CD.solver2, CD.solver3, or CD.solver4
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Calculate average coordinates for each star of interest with calc.all.ch12
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Repeat for other epochs
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Run mucalc to measure apparent proper motions (If accurate relative astrometry is wanted without proper motions, just follow steps 1-3.)
#Example
Example datasets and output for CD.solver is CD1, read.in.data is data1, and input data for mucalc is epochs3.
The measured distortion corrections contain a time varying scale factor that can either be estimated or measured. In the example below, coor.calc converts pixel coordinates (-100, 104) into RA and Dec using the [3.6] distortion correction (wa_pars1), the [3.6] pixel bias corrector (ca_pix1), image central coordinates and rotation (55.824647,32.3151426,-4.5420559), and explicitly indicating that the calculation is for channel one (1). In the first calculation, a measured scale factor (1.000083,1.000295) is used. In the second, coor.calc estimates the scale factor using the time of observations as indicated in data1. The difference between these two calculations is ~2 miliarcseconds.
data(CD1,ca_pix1,wa_pars1,data1)
options(digits=10)
- using a measured scale factor
coor.calc(ca_pix1,wa_pars1,c(55.824647,32.3151426,-4.5420559),-100,104,c(1.000083,1.000295),1)
- estimating a scale factor from HMJD.
coor.calc(ca_pix1,wa_pars1,c(55.824647,32.3151426,-4.5420559),-100,104,data1,1)