[AstroPy] Galactic UVW space motions and uncertainties in Python (a la IDL's gal_uvw)

Eric L. N. Jensen ejensen1 at swarthmore.edu
Fri Mar 6 12:00:40 EST 2015


Hi all,

I need to calculate three-dimensional Galactic space motions UVW for some stars (given position, distance, proper motion, and radial velocity as inputs), and I find that this is a task where I’m tempted to fall back on old IDL code I have, since the IDL astrolib has a gal_uvw routine to do this, and I have a complementary routine in IDL that implements the Johnson & Soderblom (1987; http://adsabs.harvard.edu/abs/1987AJ.....93..864J ) formalism for propagating uncertainties from the input quantities to the output velocities.  

I could tackle the task of translating the IDL code into Python, but realistically I’m unlikely to do so in the short term (and my knowledge of matrix algebra in Python is pretty thin), so I thought I would check and see if anyone else has done this already.   It looks like Ian Crossfield has a Python translation of gal_uvw here:  http://www.lpl.arizona.edu/~ianc/python/astrolib.html

Has anyone done the corresponding coding of the error propagation for UVW?  If not, and if anyone else is interested in this, I’d be happy to share the IDL code I have if someone wanted to translate it to Python.  It’s not very long - the trick is just getting the matrix algebra syntax translated correctly. 

Thanks in advance for your help with this,

Eric
 




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