Installation

Setting up pandeia

pandeia is the python engine behind the JWST exposure time calculator (ETC) (Pontoppidan+ 2016). jayrock uses it to simulate JWST observations locally on your machine. See the official install instructions for more information, ways to verify your installation, and a helper script. Below is an executive summary.

pandeia requires different reference datasets. Detailed install instructions are here. In short, you have to download four datasets and tell your system where to find them by setting two system variables in your .bashrc or .zshrc (← Mac users) files.

1. Download JWST reference data (4GB) and PSFs (15MB) → Section 3.1 of the instructions. Unpack them in a suitable location and set two environment variables pointing to the two unpacked directories.

Lines starting with $ are terminal commands.

export pandeia_refdata=/path/to/pandeia_data-2026.2-jwst/  # in your .bashrc or .zshrc file
export PSF_DIR=/path/to/pandeia_psfs-2026.2-jwst/  # the version (2026.2) in your files may be different

2. Download the Synphot datasets #5 (Phoenix models, 1.7GB) and #7 (JWST ETC spectra, 8.5MB) → Section 3.2. Unpack them in a suitable location and create an environment variable pointing to the newly created archive.

export PYSYN_CDBS=/path/to/synphot_datasets/trds/  # in your .bashrc or .zshrc file

Getting the directory structure of the synphot datasets right can be tricky. For reference, this is what it looks like on my system:

$ export pandeia_refdata=$HOME/astro/data/pandeia/pandeia_data-2026.2-jwst/  # line in my .zshrc file
$ export PSF_DIR=$HOME/astro/data/pandeia/pandeia_psfs-2026.2-jwst/  # line in my .zshrc file
$ export PYSYN_CDBS=$HOME/astro/data/synphot  # line in my .zshrc file
$ ls $PYSYN_CDB
comp  grid  grp
$ ls $PYSYN_CDBS/comp
acs  cos  fgs  foc  fos  hrs  hsp  nicmos  nonhst  ota  stis  wfc3  wfpc  wfpc2
$ ls $PYSYN_CDBS/grid
atmo2020  brown19  comp_qso  novae  phoenix  pne  solsys  stellar_pop  swire
$ ls $PYSYN_CDBS/grp
redcat

Installing jayrock

jayrock requires python 3.11 or higher. Install it via

pip install jayrock

This will also install all required dependencies, including common ones like numpy, pandas, astropy, astroquery, and less common ones like rocks, the client.

After installing jayrock, you can check that it installed correctly by running

import jayrock

On your first run of a jayrock script, rocks might ask to download data to a cache directory. Confirm by typing y and pressing enter.