JWST FGS countrate estimation

jwst-fgs-countrate converts guide star information from different catalogs into the expected count rate for the JWST Fine Guidance Sensor (FGS). This is done by querying the Guide Star Catalog (containing 2MASS, SDSS, and GSC2) based on the input of the guide star’s HST ID number and using information from that catalog to calculate a count rate and FGS magnitude. The code is aimed to match the version of the Guide Star Selection System used during JWST commissioning.

Example Use

Convert count rate to FGS magnitude and back

import fgscountrate
fgs_magnitude = fgscountrate.convert_cr_to_fgs_mag(fgs_countrate=1500000, guider=1)
fgs_countrate = fgscountrate.convert_fgs_mag_to_cr(fgs_magnitude=14.5, guider=2)

To compute the FGS count rate, magnitude, and errors given a guide star ID

import fgscountrate
fgs = fgscountrate.FGSCountrate(guide_star_id='N13I000018', guider=1)
cr, cr_err, mag, mag_err = fgs.query_fgs_countrate_magnitude()

The count rate and magnitude calculations are also saved in attributes

# Count rate and Magnitude attributes
fgs.fgs_countrate
fgs.fgs_countrate_err
fgs.fgs_magnitude
fgs.fgs_magnitude_err

To get the guide star data from the guide star catalog

# After doing the count rate calculation, access the gsc_series attribute
import fgscountrate
fgs = fgscountrate.FGSCountrate(guide_star_id='N13I000018', guider=1)
fgs_countrate = fgs.query_fgs_countrate_magnitude()
fgs.gsc_series

# Or independent of the count rate calculation, use query_gsc() to return a Pandas dataframe
from fgscountrate.utils import query_gsc
data = query_gsc(gs_id='N13I000018')

To learn which conversions were used when calculating the J, H, and K magnitudes

# Conversion method attributes
fgs.j_convert_method
fgs.h_convert_method
fgs.k_convert_method

Or to access any of the individual JHK conversion equations

# Using already known data
from fgscountrate import conversions
g_mag = 14.5
g_mag_err = 0.1
z_mag = 15.2
z_mag_err = 0.1
j_mag = conversions.convert_sdssgz_to_jhk(data=(g_mag, g_mag_err, z_mag, z_mag_err), output_mag='J')

# Using data queried from the GSC using query_gsc()
from fgscountrate import conversions
from fgscountrate.utils import query_gsc
dataframe = query_gsc(gs_id='N13I000018')
dataseries = dataframe.iloc[0]
j_mag = conversions.convert_sdssgz_to_jhk(data=dataseries, output_mag='J')

To get the data from the step by step calculations for the FGS countrate and magnitude

# Returns a dataframe
fgs.band_dataframe

Versioning

This repository follows the principles of "Semantic Versioning", such that

Given a version number MAJOR.MINOR.PATCH, increment the:

1. MAJOR version when you make incompatible API changes,
2. MINOR version when you add functionality in a backwards compatible manner, and
3. PATCH version when you make backwards compatible bug fixes.

When releasing a new version, developers should change the version number in setup.py, merge this change in a PR, and then release the package via the GitHub interface.

Collaborators

• Sherie Holfeltz (@stholfeltz)
• Pierre Chayer

Former Developer

• Shannon Osborne (@shanosborne)

License

This project is Copyright (c) Space Telescope Science Institute and licensed under the terms of the Aura license. This package is based upon the Astropy package template which is licensed under the BSD 3-clause licence. See the licenses folder for more information.