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Abstract The rotation period of a star is an important quantity that provides insight into its structure and state. For stars with surface features like starspots, their periods can be inferred from brightness variations as these features move across the stellar surface. TESS, with its all-sky coverage, is providing the largest sample of stars for obtaining rotation periods. However, most of the periods have been limited to shorter than the 13.7 days TESS orbital period due to strong background signals (e.g., scattered light) on those timescales. In this study, we investigated the viability of measuring longer periods (>10 days) from TESS light curves for stars in the Northern Continuous Viewing Zone (NCVZ). We first created a reference set of 272 period measurements longer than 10 days for K and M dwarfs in the NCVZ using data from the Zwicky Transient Facility (ZTF) that we consider as the “ground truth” given ZTF’s long temporal baseline of 6+ years. We then used theunpopularpipeline to detrend TESS light curves and implemented a modified Lomb–Scargle (LS) periodogram that accounts for flux offsets between observing sectors. For 179 out of the 272 sources (66%), the TESS-derived periods match the ZTF-derived periods to within 10%. The match rate increases to 81% (137 out of 170) when restricting to sources with a TESS LS power that exceeds a threshold. Our results confirm the capability of measuring periods longer than 10 days from TESS data, highlighting the data set’s potential for studying slow rotators.
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Quantifying the Limits of TESS Stellar Rotation Measurements with the K2-TESS Overlap
The Transiting Exoplanet Survey Satellite (TESS) has provided stellar rotation periods across much of the sky through high-precision light curves, but the reliability and completeness of these measurements require careful evaluation. We assess the accuracy of TESS-derived rotation periods by leveraging a cross-matched sample of ∼23,000 stars observed by both TESS and the K2 mission, treating K2 periods as a benchmark. Using causal pixel models to extract light curves and a Lomb–Scargle (LS) periodogram to identify rotation signals, we quantify the empirical uncertainties, reliability, and completeness of TESS rotation period measurements. We find that uncertainties on TESS-derived rotation periods are typically below 3% for stars with periods <10 days. Rotation periods are generally reliable out to 10 days, with ≳80% of measurements matching the K2 benchmark. Completeness and reliability drop dramatically for periods beyond ≃12 days due to the 27 day sector limitation. Stricter cuts on TESS magnitude and LS power improve reliability; the highest LS power tested (>0.2) ensures >90% reliability below 10 days but removes over half of potential detections. Stitching consecutive-sector light curves reduces period uncertainties but does not improve overall reliability or completeness due to persistent systematics. Our findings and code provide a framework for interpreting TESS-derived rotation periods and inform the selection of quality cuts to optimize studies of stellar rotation, young associations, and gyrochronology.
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- Award ID(s):
- 2143763
- PAR ID:
- 10671749
- Publisher / Repository:
- Astrophysical Journal
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 985
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 233
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.3847/1538-4357/adcecc
