Frequently asked questions

What happens for stars cooler than 3800 K?

For stars with measured effective temperatures outside of our calibrated range (3800-6200 K), we have opted to force our model to return NaN age posteriors. For stars near the boundary (e.g., 3800+/-100 K) for which a portion of the likelihood is outside our nominal temperature range, the returned posterior includes that region through a local extrapolation of the mean polynomial models discussed in BPH23.

The same point applies for stars hotter than 6200 K.

What happens for stars younger than 80 Myr?

For stars younger than 0.08 Gyr, we fixed our “mean rotation period model” to equal the lowest reference polynomial rotation period values, as set by the α Per cluster. This yields posterior distributions that are uniformly distributed at ages younger than 0.08 Gyr. So, the age posteriors for such systems will be upper limits, which may or may not be useful for you!

Once stars begin getting this young, there are other age-dating techniques that may be more constraining. For instance, you might search spectra for lithium absorption, check broadband photometry for near-infrared excesses, or analyze HR diagrams for evidence of pre-main-sequence evolution.

What happens for stars older than 2.6 Gyr?

For stars older than 2.6 Gyr, we have implemented a few possible extrapolation approaches. Our default adopted approach, the pchip_m67 extrapolation, provides one plausible interpolation between 2.6 and 4 Gyr based on the M67 data, though it is subject to larger systematic errors than e.g., our model between 1 and 2.6 Gyr because the change of the slope in rotation period versus time is not as well-constrained. After 4 Gyr, as for α Per we simply force the mean model’s rotation period to equal the highest reference rotation period values, but now as set by M67. This yields posterior probability distributions that are uniformly distributed at ages older than 4 Gyr.

So, the age posteriors for such systems will be lower limits, and they may or may not be useful for you!

Are there movies?

Yes! This movie shows random draws from the model over the first two gigayears. This movie compares these random draws to available cluster data at fixed timesteps.