Andrew Mann

TARS: the TESS All-Sky Rotation Survey

Each dot is a fast-spinning (and therefore young) star from TARS. The animation keeps only stars moving at a given speed relative to the Sun; as that speed changes, groups of young stars moving together pop out of the background.

Young stars spin fast. A star is born rotating quickly and gradually slows down as its magnetized wind carries away angular momentum, so a rotation period is a rough clock: a star spinning once every day or two is very likely young. Spots on the star's surface rotate in and out of view, and the brightness changes they cause let us measure the period from a light curve.

NASA's TESS mission has now observed nearly the entire sky. TARS uses those light curves to measure rotation periods for 1,046,317 stars within 500 parsecs of the Sun. The catalog, light curves, and periodograms are public at MAST and on Zenodo. Andy Boyle led the catalog paper, I maintain the catalog, and the work is part of our NASA Astrophysics Data Analysis Program project, "Gyro-Tagging."

TESS sky coverage building up from 2018 to 2026, with familiar constellations for reference.

On its own, rotation is a noisy age indicator for any single star. Its power is in numbers. Combine rotation with positions and motions from ESA's Gaia mission, keep only the fast rotators, and young populations stand out clearly from the much larger background of older field stars. That is how we found that the Pleiades is just the core of a much larger, dissolving structure, the Greater Pleiades Complex.

We also test where rotation periods from TESS can be trusted, using stars that K2 observed with longer baselines, and calibrate rotation as an age clock using benchmark clusters like NGC 752 (see gyrochronology).

Papers

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