jaxtromet

astromet.py (https://github.com/zpenoyre/astromet.py) rewritten to JAX.

Install

To install requirements.txt with conda:

conda install -c conda-forge -y --file requirements.txt

In case of problems with astromet and/or jax installation, refer to https://github.com/google/jax and install with pip. Beware of the caveats of using conda and pip install simultaneously: https://www.anaconda.com/blog/using-pip-in-a-conda-environment.

If you wish to use the conda enivronment's pip, use:

<path/to/conda>/envs/<env-name>/bin/pip install ...

Main changes from astromet

I tried to make the API as consistent as possible, and the only changes I have made were due to differences coming from JAX and some computational overhead or complexity they would cause.

JAX random sampling

pseudo-random numbers work a bit differently in JAX. ensure to create some seed at the beginning, like:

key = jax.random.PRNGKey(10)

and regenerate a key every step in some loop, if you want to sample.

for ...:
    key, _ = jax.random.split(key, 2)
    (...) # pass the key as an argument

define_lens

• I have ommited the definition of params as a class and using a custom dict wrapper instead (so params have to be converted to dict: dict(params) to pass them into functions)
• No baseline magnitude is passed (m0 parameter) because it wasn't used.
• t_0 and t_E parameters are now passed in decimal years to omit the conversion using astropy inside the function.

Example of converting t_0 from reduced JD to decimal year:

from astropy.time import Time
t_0_jyear = Time(t_0+2450000., format='jd').jyear

Example of converting t_E from days to jyear:

import astropy.units as u
t_E_jyear = (tE*u.day).to(u.year)

mock_obs

a jax key has to be passed to sample errors (if errors are not zero)

key, _ = jax.random.split(jax.random.PRNGKey(100), 2)
t_obs, rac_obs, dec_obs = mock_obs(ts, phis, racs, decs, jaxtromet.sigma_ast(magnitude_0), key)

fit

Barycentric positions (bs) are now calculated for the passed times outside the loop. This can be done using the barycentricPosition function in jaxtromet. It uses external libraries and therefore cannot be jitted (easily).

bs = jaxtromet.barycentricPosition(ts)

def fit(ts, bs, xs, phis, xerr, ra, dec, G=12, epoch=2016.0)

track

Same situation as in fit - barycentric positions have to be passed.

The parameters have to be converted to a normal dict (JAX doesn't accept other datatypes e.g. custom classes).

def track(ts, bs, dict(ps))

astromet.py

Please take a look at the wonderful job done by Zephyr Penoyre and their team.

A simple python package for generating astrometric tracks of single stars and the center of light of unresolved binary, blended and lensed systems. Includes a close emulation of Gaia's astrometric fitting pipeline.

https://astrometpy.readthedocs.io/en/latest/

pip install astromet

Still in development, functional but may occasional bugs or future changes. Get in touch with issues/suggestions.

Requires

• numpy
• astropy
• scipy
• matplotlib (for notebooks)