Frequently Asked Questions

Where Does LightCurveLynx Store Downloaded Data?

LightCurveLynx downloads data files (e.g., OpSim tables, passbands, dust maps) on demand and caches them so they do not need to be re-downloaded on subsequent runs. The cache location is resolved in the following priority order:

The LIGHTCURVELYNX_DATA_DIR environment variable, if set.
$XDG_CACHE_HOME/lightcurvelynx, if XDG_CACHE_HOME is set.
~/.cache/lightcurvelynx (default).

To redirect the cache to a custom location — for example on an HPC system where the home directory is read-only or quota-limited — set the environment variable before running your code:

export LIGHTCURVELYNX_DATA_DIR=/path/to/your/cache

or inline in Python before importing LightCurveLynx:

import os
os.environ["LIGHTCURVELYNX_DATA_DIR"] = "/path/to/your/cache"

How Can I See More Detailed Output During Simulation?

You can enable more detailed logging output by configuring the logging level for LightCurveLynx. For example, to see info-level messages, you can add the following code snippet before running your simulation:

import logging
logging.basicConfig(level=logging.INFO)

You can also use logging.DEBUG to see even more detailed debug-level messages.

I Am Seeing Empty Light Curves for Some Entries. Why Is This Happening?

The most common reason that LightCurveLynx produces rows with empty light curves is that the object’s sampled position (RA, dec) lies outside the area covered by the survey. This can happen even if you use one of the predefined samplers, such as the ApproximateMOCSampler, because all of the samplers are approximate.

You can find the empty rows in your results using:

idx = results.lightcurve.isna()

and check whether the row was observed using the ObsTable.get_observations() function with the corresponding RA and dec.

Can I Use a Random Seed to Get Reproducible Results?

Yes. LightCurveLynx allows the user to control randomness by passing in a predefined random number generator via the rng parameter in the simulate_lightcurves() function. If the user provides a random number generator with a fixed seed, then the results of the simulation will be reproducible.

Can I Use a Random Seed with Parallelization?

Yes. See the parallelization notebook for details.

How Do I Use an External Simulation Package?

LightCurveLynx is designed to be modular and extensible, allowing users to wrap external simulation packages for use within the LightCurveLynx framework. How you wrap the package will depend largely on the specifics of the package you are trying to wrap. We have provided a few demo notebooks to illustrate various approachs, including:

Wrapping Bagle Models

Wrapping Redback Models

Wrapping VBMicrolensing

The LightCurveLynx team is also happy to help you wrap your favorite package. Please reach out if you have questions or need assistance.

Can I Combine Multiple Surveys in a Single Simulation?

Yes. LightCurveLynx allows you to combine multiple surveys in a single simulation by passing in multiple observation tables and corresponding passband groups. See the multiple surveys demo notebook for an example of how to do this.

Can I Simulate Spectra?

Yes with some caveats. LightCurveLynx has built-in support for simulating spectra, but it is currently in an early stage of development and does not yet add noise to the measurements. In addition, spectra simulation is only compaible with models that generate data on the spectral level (not bandflux-only models). For more detail see the spectrograph demo notebook.

Can I Generate Points from a Catalog?

Yes. LightCurveLynx allows you to generate light curves for objects in a catalog containing positions using the``CatalogRADECSampler`` object This sampler takes in a table of information with at least “ra” and “dec” columns. The helper function from_hats() is provided to load directly from a [HATS](https://www.ivoa.net/documents/Notes/HATS/) catalog.

See the sampling positions demo notebook notebook for a detailed description of how to sample (RA, dec) positions.

Why does my light curve have multiple points at the same time?

While this can legitimately happen if multiple surveys have the exact same MJD for an observations, this is more likely an artifact of per-CCD level information. If the survey data is provided at the CCD-level (such as with Rubin’s DP1 CCD visit table) and no detector footprint is set, the code will estimate a circular footprint per-CCD. Points that lie near the edge of one CCD may also be picked up by another CCD. This can often be solved by setting the detector footprint for each CCD. See the ccd-level obstable for more information.