Gyrochronology is the empirical relation between rotation and age. NASA's Transiting Exoplanet Survey Satellite (TESS), Kepler, and K2 missions have observed thousands of wide main sequence binaries. Since components of a binary are coeval, their rotation periods should be consistent with gyrochronology models. However, the usefulness of gyrochronology depends upon reliable rotation periods. We explore the reliability of rotation period determinations for a sample of wide binary components from the TESS cycle 3. Wide binaries with the most reliable rotation period determinations provide a strong basis for testing whether the gyrochronology empirical relation derived from open clusters is also valid for field stars.
]]>Many open questions remain to be answered before gyrochronology can be established as a reliable method for 20 determining stellar ages. For example, why do old stars rotate faster than expected by Skumanich's linear prediction? 21 (Skumanich 1972), why does the period-age relation for lower main sequence stars appear to be degenerate? Further 22 studies that would like to tackle such concerns will require well-determined rotation periods for systems of the same 23 age.
Open clusters have been the canonical systems for gyrochronology research (e.g., Barnes 2007). However, in a recent 25 study by Gruner et al. (2023), wide binary (WB) systems have shown promising results. They can be considered the 26 smallest type of open clusters, as both stars in the system share the same origin and, thus, the same age. Further, 27 both system components are separated enough to be considered equivalent to field stars with a similar wide range of 28 metallicities.
We compiled a sample of 1956 WBs observed by TESS cycle 3 (sectors 27 to 39) for gyrochronology research purposes.
We create custom masks for each target using the approach outlined in Nielsen et al. (2020) and Metcalfe et al. (2023).
To prepare the light curves, we normalize each sector relative to its median flux and gap fill using spline interpolation.
We determined rotation periods for each of the 3912 components by choosing the period with the highest amplitude 33 in Lomb-Scargle periodograms (LS), the peak with the highest amplitude after P = 0 in auto-correlation functions 34 (ACF), and the peak with the highest relative amplitude in wavelet analyses using Morlet wavelet transform with k0 35 = 6 (WVL). To provide a valid test of gyrochronology, it is essential to confirm that the periods detected are, in fact, 36 due to stellar rotation.
Common challenges in ascertaining stellar rotation periods can be categorized into two primary sources: those 38 inherent to the physics of the rotation phenomenon and those related to the instrument. The first category involves 39 the ambiguity in determining the correct period when there are harmonics of the rotation period. Such situations occur 40 when there are surface spots in opposite hemispheres, (i.e., double dippers, Basri & Nguyen 2018) or when the angle of 41 inclination of the observation results in a non-sinusoidal shape of the light-curve (Santos et al. 2017). Likewise, a close 42 companion to the actual target results in blended light curves, which would also complicate period determinations.