Periodic stellar variability from almost a million NGTS light curves

Joshua T Briegal, Edward Gillen, Didier Queloz, Simon Hodgkin, Jack S Acton, David R Anderson, David J Armstrong, Matthew P Battley, Daniel Bayliss, Matthew R Burleigh, Edward M Bryant, Sarah L Casewell, Jean C Costes, Philipp Eigmüller, Samuel Gill, Michael R Goad, Maximilian N Günther, Beth A Henderson, James A G Jackman, James S JenkinsLars T Kreutzer, Maximiliano Moyano, Monika Lendl, Gareth D Smith, Rosanna H Tilbrook, Christopher A Watson, Richard G West, Peter J Wheatley

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We analyse 829 481 stars from the Next Generation Transit Survey (NGTS) to extract variability periods. We utilize a generalization of the autocorrelation function (the G-ACF), which applies to irregularly sampled time series data. We extract variability periods for 16 880 stars from late-A through to mid-M spectral types and periods between ∼0.1 and 130 d with no assumed variability model. We find variable signals associated with a number of astrophysical phenomena, including stellar rotation, pulsations, and multiple-star systems. The extracted variability periods are compared with stellar parameters taken from Gaia DR2, which allows us to identify distinct regions of variability in the Hertzsprung–Russell Diagram. We explore a sample of rotational main-sequence objects in period-colour space, in which we observe a dearth of rotation periods between 15 and 25 d. This ‘bi-modality’ was previously only seen in space-based data. We demonstrate that stars in sub-samples above and below the period gap appear to arise from a stellar population not significantly contaminated by excess multiple systems. We also observe a small population of long-period variable M-dwarfs, which highlight a departure from the predictions made by rotational evolution models fitted to solar-type main-sequence objects. The NGTS data spans a period and spectral type range that links previous rotation studies such as those using data from Kepler, K2, and MEarth.
Original languageEnglish
Pages (from-to)420-438
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date05 Apr 2022
Publication statusPublished - 01 Jun 2022


  • Space and Planetary Science
  • Astronomy and Astrophysics


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