Caveats

Stellar Evolution

This code models the ensemble evolution of rotation periods for main-sequence stars with temperatures of 3800-6200 K (masses of 0.5-1.2 solar). The calibration data for the model span 0.08-2.6 Gyr. At younger ages, rotation periods are less predictive of age, and other age indicators may be more useful. At older ages, the effects of stellar evolution begin to become important, especially for the more massive stars.

If you have auxiliary data, such as stellar surface gravities derived from spectra, they can help determine whether your star might have undergone significant nuclear evolution – in other words whether it is a subgiant or even a giant. If it is, this model is not applicable.

Binarity

Before applying gyrochronology, it’s worth asking whether your star might be a binary. If it is, you should proceed carefully. Binarity can observationally bias temperature and rotation period measurements. There is also a physical concern that even a widely-separated companion might influence a star’s spin-down, by encouraging early dispersal of the protostellar disk.

A few ways to determine whether your star might be a binary include:

  • Get high resolution images, and determine whether there are nearby companions. You can also check the Gaia point source catalog for such companions, though you may not achieve the same contrast limits close to the star.

  • Check the Gaia point source catalog for whether the renormalized unit weight error (RUWE) exceeds some threshold. Additional astrometric scatter, which is what this quantity measures, can be caused by either a marginally resolved point source, or by astrometric binarity.

  • Obtain spectra, and check if they are double-lined, or if they show significant radial variations over time. The radial_velocity_error column in Gaia DR3 can help diagnose the latter case, although care should be taken for stars that are faint and have low S/N spectra.

  • Query the Gaia point source catalog in a local spatial volume around your star. With the resulting sample of stars, check whether your star is an outlier in the HR diagram. This can be an indication of photometric binarity.

As mentioned in the section on Visual interpolation for a star’s age, the same types of considerations apply to hot Jupiter systems, or any kinds of systems in which tidal effects might alter the star’s rotation period.

Generally speaking, the best approaches will differ based on your stars of interest. A few separate utilities that can help in assessing these types of utilties are available through astroquery.gaia, and cdips.utils.gaiaqueries. Both are pip-installable.