Question about Scattering Measure (sm)

[JuanLebronMedina]

I wish to use the values for the Scattering Measure (sm) and/or Pulse Broadening Time (tausis) but I have not been able to get them from pygedm. Any examples of how to extract this values from pygedm.

Thank you

[telegraphic]

Hi @DemonLord13,

This could probably be improved (help welcome -- I haven't used this output much!)

In the short term, you can get this by using the ne21c compiled object manually:

import ne21c

In [11]: ne21c.dist_to_dm(0,0,1)
Out[11]:
{'dm': 35.437896728515625,
 'sm': 0.0010428746463730931,
 'smiso': 0.0006964090862311423,
 'smtau': 0.000870048301294446,
 'smtheta': 0.0002934452786576003}

However, this will only work if you cd into the pygedm directory, where the data files are (you can see in ipython by):

In [7]: pygedm
Out[7]: <module 'pygedm' from '/Users/dcprice/mpy3/lib/python3.9/site-packages/pygedm/__init__.py'>

cd /Users/dcprice/mpy3/lib/python3.9/site-packages/pygedm

There is a run_from_pkgdir function that is used to make sure that the ne21c wrapper always runs in the right directory when called in pygedm.

Longer term, we should make this more accessible. One way would be to add an extra argument to dist_to_dm and dm_to_dist in the ne2001_wrapper.py, to enable full output (e.g. raw_output=True). Or we could create new functions?

[JuanLebronMedina]

I think that the best solutions is adding this function to ne2001_wrapper.py but with a different name like dist_to_dm_extra and dm_to_dist_extra with the comments like the other functions (Those comments are really helpful). Changing dist_to_dm and dm_to_dist on the ne2001_wrapper.py will cause other people codes stop working because the new output. New functions will prevent this problem.

[JuanLebronMedina]

I tried to run ne21c.dm_to_dist compare it to pygedm.dm_to_dist using the same input I get different distances and smtau values.

[JuanLebronMedina]

Here is the easier way I manage to get the sm value for my self. Did changes to the ne2001_wrapper.py on the def TAUISS(d,sm,nu).

For people who need sm I recommend this but for the future if pygedm gives this value would be better.

[telegraphic]

Hi @DemonLord13, the latest version adds a full_output argument to the dm_to_dist and dist_to_dm routines in the ne2001_wrapper.py:

def dist_to_dm(l, b, dist, nu=1.0, full_output=False):
    """ Convert distance to DM and compute scattering timescale

    Args:
        l (float): galactic longitude in degrees
        b (float): galactic latitude in degrees
        dist (float): Distance in kpc
        nu (float in GHz or astropy.Quantity): observing frequency (GHz)
        full_output (bool): Return full raw output (dict) from NE2001 if set to True
    """

[telegraphic]

Ok, new version, 3.3.0, uploaded to PyPi -- @DemonLord13 would be great if you can check this works :)

[JuanLebronMedina]

Hi @telegraphic the calculation for nu is working but I am having problem with the full output

[JuanLebronMedina]

This worked

[telegraphic]

Great! Yep I only added this to the ne2001 wrapper, as ymw16 doesn't predict SM