pRVsim is a Python package for generating synthetic precision radial velocity (pRV) observations for a given star, instrument, and planetary system. It operates in a 2D spectral (2DS) format, where each spectrograph order is simulated independently.
This tool is useful for understanding when a template is a good tool to use for radial velocity measurements.
- Generate PHOENIX synthetic stellar spectra for given stellar parameters
- Define instruments and spectrograph orders
- Inject planetary RV curves
- Create synthetic observations
- Flexible template construction from individual observations
- Do RV estimation using a template-matching algorithm
- Modular structure for testing different configurations
Currently, only SPIRou and NIRPS are supported with actual wavelength sampling data. However, users can also define hypothetical instruments by specifying a constant sampling resolution (e.g., uniform spacing in velocity per pixel). This enables broader testing and flexibility for new or theoretical designs.
At this stage, the simulation only includes photon noise. Other sources of noise such as instrumental systematics, tellurics, or stellar activity are not yet implemented. This makes pRVsim ideal for isolating and understanding the limits imposed purely by photon statistics.
There are two main ways to use pRVsim:
To explore the code on a per-order basis, use the Jupyter notebook located in the test/ folder:
test/tutorial.ipynb
This notebook allows you to:
- Define a high-resolution stellar spectrum
- Choose an instrument and order to define the wavelength range
- Set the desired signal-to-noise ratio (SNR) in terms of counts per 1 km/s pixel
- Create synthetic observations
- Create templates
- Do RV estimation
Note on SNR: The SNR value refers to the flux counts for a 1 km/s pixel. For example, if your detector has 500 m/s pixel size and you want ~10,000 photon counts per pixel, you should input an SNR of around 140.
For running a full simulation across all desired orders and generating output data files, use the following two scripts in the test/ folder:
python json_creator.py --param your_json_file.jsonpython run_experiment.py --param your_json_file.json --output your_results_file.dfThis will simulate the full RV experiment using your defined setup and save the results to a DataFrame file.
Currently, the RV curve is generated by providing:
- A date range
- The number of desired observations
- The RV semi-amplitude (K) of the planetary system
Observation dates are randomized within your given range. The barycentric Earth radial velocity (BERV) is computed for each date. You can also modify Earth-based observational parameters such as observatory longitude and latitude.
At present, the planetary RV curve assumes a circular orbit with a fixed orbital frequency of 0.08. Future versions will allow for:
- Predefined sets of observation dates
- Arbitrary orbital configurations, including eccentric or multi-planet systems