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Enhanced magnetic activity in rapidly rotating binary stars

Nature Astronomy (2025)Cite this article

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Abstract

Stellar activity is fundamental to stellar evolution and the formation and habitability of exoplanets. Magnetic surface activity is driven by the interaction between convective motions and rotation in cool stars, resulting in a dynamo process. In single stars, activity increases with rotation rate until it saturates for stars with rotation periods Prot < 3–10 d. However, the mechanism responsible for saturation remains unclear. Observations indicate that red giants in binary systems that are in spin–orbit resonance exhibit stronger chromospheric activity than single stars with similar rotation rates, suggesting that tidal flows can influence surface activity. Here, we investigate the chromospheric activity of main-sequence binary stars to understand the impact of tidal forces on saturation phenomena. For binaries with 0.5 < Prot (d) < 1, mainly contact binaries that share a common thermal envelope, we find enhanced activity rather than saturation. This result supports theoretical predictions that a large-scale α–ω dynamo during common-envelope evolution can generate strong magnetic fields. We also observe supersaturation in chromospheric activity, a phenomenon tentatively noted previously in coronal activity, where activity levels fall below saturation and decrease with shorter rotation periods. Our findings emphasize the importance of studying stellar activity in stars with extreme properties compared with the Sun’s.

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Fig. 1: Chromospheric activity of close binaries on circular orbits.
Fig. 2: Comparison of magnetic activity between single and binary stars.
Fig. 3: Filling factors for 1,348 Gaia eclipsing binaries with log \({R}_{{\rm{HK}}}^{{\prime}}\) measurements.
Fig. 4: Chromospheric activity of close binaries and its relation with orbital eccentricity and stellar mass.

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Data availability

The data required to reproduce the figures presented in this work can be found in Supplementary Data 1–8 and are publicly available via GitHub at https://github.com/Jieyu126/CloseBinaryActivity.git. The low- and medium-resolution spectra, spectral-type classifications and stellar atmospheric parameters used in this study are available from the LAMOST DR9 survey, accessible at http://www.lamost.org/dr9/v2.0/catalogue. Orbital solutions of binary systems from the Gaia DR3 catalogue can be accessed through the Gaia archive: https://gea.esac.esa.int/archive/.

Code availability

The code used in this work is publicly available via GitHub at https://github.com/Jieyu126/CloseBinaryActivity.git.

References

  1. Basri, G. An Introduction to Stellar Magnetic Activity (IOP Publishing, 2021).

  2. Brun, A. S. & Browning, M. K. Magnetism, dynamo action and the solar–stellar connection. Living Rev. Sol. Phys. 14, 4 (2017).

    Article  ADS  Google Scholar 

  3. Cameron, R. H. & Schüssler, M. Observationally guided models for the solar dynamo and the role of the surface field. Space Sci. Rev. 219, 60 (2023).

    Article  ADS  Google Scholar 

  4. Egeland, R. et al. The Mount Wilson Observatory S-index of the Sun. Astrophys. J. 835, 25 (2017).

    Article  ADS  Google Scholar 

  5. Sowmya, K. et al. Modeling stellar Ca ii H and K emission variations. I. Effect of inclination on the S-index. Astrophys. J. 914, 21 (2021).

    Article  ADS  Google Scholar 

  6. Luhn, J. K., Wright, J. T., Howard, A. W. & Isaacson, H. Astrophysical insights into radial velocity jitter from an analysis of 600 planet-search stars. Astron. J. 159, 235 (2020).

    Article  ADS  Google Scholar 

  7. Gehan, C., Gaulme, P. & Yu, J. Surface magnetism of rapidly rotating red giants: single versus close binary stars. Astron. Astrophys. 668, A116 (2022).

    Article  ADS  Google Scholar 

  8. Large Sky Area Multi-Object Fiber Spectroscopic Telescope Data Release 9 (National Astronomical Observatories, Chinese Academy of Sciences, 2023); https://www.lamost.org/dr9/

  9. Cui, X.-Q. et al. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Res. Astron. Astrophys. 12, 1197–1242 (2012).

    Article  ADS  Google Scholar 

  10. Arenou, F. et al. Gaia Data Release 3—stellar multiplicity, a teaser for the hidden treasure. Astron. Astrophys. 674, A34 (2023).

    Article  Google Scholar 

  11. Zahn, J. P. & Bouchet, L. Tidal evolution of close binary stars. II. Orbital circularization of late-type binaries. Astron. Astrophys. 223, 112–118 (1989).

    ADS  Google Scholar 

  12. Barker, A. J. Tidal dissipation due to inertial waves can explain the circularization periods of solar-type binaries. Astrophys. J. Lett. 927, L36 (2022).

    Article  ADS  Google Scholar 

  13. Bashi, D., Mazeh, T. & Faigler, S. Features of Gaia DR3 spectroscopic binaries I. Tidal circularization of main-sequence stars. Mon. Not. R. Astron. Soc. 522, 1184–1195 (2023).

    Article  ADS  Google Scholar 

  14. Zahn, J. P. Tidal evolution of close binary stars. I—Revisiting the theory of the equilibrium tide. Astron. Astrophys. 220, 112–116 (1989).

    ADS  Google Scholar 

  15. Lurie, J. C. et al. Tidal synchronization and differential rotation of Kepler eclipsing binaries. Astron. J. 154, 250 (2017).

    Article  ADS  Google Scholar 

  16. Dewberry, J. W. & Wu, Y. Testing tidal theory using Gaia binaries: the red giant branch. Astrophys. J. 984, 137 (2025).

    Article  Google Scholar 

  17. Gaulme, P., Jackiewicz, J., Appourchaux, T. & Mosser, B. Surface activity and oscillation amplitudes of red giants in eclipsing binaries. Astrophys. J. 785, 5 (2014).

    Article  ADS  Google Scholar 

  18. Gaulme, P. et al. Active red giants: close binaries versus single rapid rotators. Astron. Astrophys. 639, A63 (2020).

    Article  Google Scholar 

  19. Benbakoura, M. et al. Spectroscopic and seismic analysis of red giants in eclipsing binaries discovered by Kepler. Astron. Astrophys. 648, A113 (2021).

    Article  Google Scholar 

  20. Gehan, C., Godoy-Rivera, D. & Gaulme, P. Magnetic activity of red giants: correlation between the amplitude of solar-like oscillations and chromospheric indicators. Astron. Astrophys. 686, A93 (2024).

    Article  ADS  Google Scholar 

  21. Hall, D. S. in Multiple Periodic Variable Stars Vol. 60 (ed. Fitch, W. S.) 287–348 (Springer, 1976).

  22. Jayasinghe, T. et al. The ASAS-SN catalogue of variable stars—VII. Contact binaries are different above and below the Kraft break. Mon. Not. R. Astron. Soc. 493, 4045–4057 (2020).

    Article  ADS  Google Scholar 

  23. Santos, A. R. G. et al. Surface rotation and photometric activity for Kepler targets. I. M and K main-sequence stars. Astrophys. J. Suppl. Ser. 244, 21 (2019).

    Article  ADS  Google Scholar 

  24. Santos, A. R. G., Breton, S. N., Mathur, S. & García, R. A. Surface rotation and photometric activity for Kepler targets. II. G and F main-sequence stars and cool subgiant stars. Astrophys. J. Suppl. Ser. 255, 17 (2021).

    Article  ADS  Google Scholar 

  25. Reinhold, T. & Hekker, S. Stellar rotation periods from K2 Campaigns 0–18: evidence for rotation period bimodality and simultaneous variability decrease. Astron. Astrophys. 635, A43 (2020).

    Article  ADS  Google Scholar 

  26. Wright, N. J., Drake, J. J., Mamajek, E. E. & Henry, G. W. The stellar-activity–rotation relationship and the evolution of stellar dynamos. Astrophys. J. 743, 48 (2011).

    Article  ADS  Google Scholar 

  27. Fang, X.-S., Zhao, G., Zhao, J.-K. & Bharat Kumar, Y. Stellar activity with LAMOST—II. Chromospheric activity in open clusters. Mon. Not. R. Astron. Soc. 476, 908–926 (2018).

    Article  ADS  Google Scholar 

  28. Noyes, R. W., Hartmann, L. W., Baliunas, S. L., Duncan, D. K. & Vaughan, A. H. Rotation, convection, and magnetic activity in lower main-sequence stars. Astrophys. J. 279, 763–777 (1984).

    Article  ADS  Google Scholar 

  29. Frasca, A. et al. The Gaia-ESO Survey: chromospheric emission, accretion properties, and rotation in γ Velorum and Chamaeleon I. Astron. Astrophys. 575, A4 (2015).

    Article  Google Scholar 

  30. Newton, E. R. et al. The Hα emission of nearby M dwarfs and its relation to stellar rotation. Astrophys. J. 834, 85 (2017).

    Article  ADS  Google Scholar 

  31. Suárez Mascareño, A. et al. HADES RV programme with HARPS-N at TNG: VII. Rotation and activity of M-dwarfs from time-series high-resolution spectroscopy of chromospheric indicators. Astron. Astrophys. 612, A89 (2018).

    Article  Google Scholar 

  32. Núñez, A. et al. The factory and the beehive. V. Chromospheric and coronal activity and its dependence on rotation in Praesepe and the Hyades. Astrophys. J. 962, 12 (2024).

    Article  ADS  Google Scholar 

  33. Skumanich, A. Time scales for Ca ii emission decay, rotational braking, and lithium depletion. Astrophys. J. 171, 565–567 (1972).

    Article  ADS  Google Scholar 

  34. Pizzolato, N., Maggio, A., Micela, G., Sciortino, S. & Ventura, P. The stellar activity–rotation relationship revisited: dependence of saturated and non-saturated X-ray emission regimes on stellar mass for late-type dwarfs. Astron. Astrophys. 397, 147–157 (2003).

    Article  ADS  Google Scholar 

  35. Reiners, A., Schüssler, M. & Passegger, V. M. Generalized investigation of the rotation–activity relation: favoring rotation period instead of Rossby number. Astrophys. J. 794, 144 (2014).

    Article  ADS  Google Scholar 

  36. Reiners, A. et al. Magnetism, rotation, and nonthermal emission in cool stars: average magnetic field measurements in 292 M dwarfs. Astron. Astrophys. 662, A41 (2022).

    Article  Google Scholar 

  37. Regős, E. & Tout, C. A. The effect of magnetic fields in common-envelope evolution on the formation of cataclysmic variables. Mon. Not. R. Astron. Soc. 273, 146–156 (1995).

    Article  ADS  Google Scholar 

  38. Tout, C. A., Wickramasinghe, D. T., Liebert, J., Ferrario, L. & Pringle, J. E. Binary star origin of high field magnetic white dwarfs. Mon. Not. R. Astron. Soc. 387, 897–901 (2008).

    Article  ADS  Google Scholar 

  39. Potter, A. T. & Tout, C. A. Magnetic field evolution of white dwarfs in strongly interacting binary star systems. Mon. Not. R. Astron. Soc. 402, 1072–1080 (2010).

    Article  ADS  Google Scholar 

  40. Nordhaus, J., Wellons, S., Spiegel, D. S., Metzger, B. D. & Blackman, E. G. Formation of high-field magnetic white dwarfs from common envelopes. Proc. Natl Acad. Sci. USA 108, 3135–3140 (2011).

    Article  ADS  Google Scholar 

  41. Röpke, F. K. & De Marco, O. Simulations of common-envelope evolution in binary stellar systems: physical models and numerical techniques. Living Rev. Comput. Astrophys. 9, 2 (2023).

    Article  ADS  Google Scholar 

  42. Randich, S., Schmitt, J. H. M. M., Prosser, C. F. & Stauffer, J. R. The X-ray properties of the young open cluster around α Persei. Astron. Astrophys. 305, 785–805 (1996).

    ADS  Google Scholar 

  43. Randich, S. Supersaturation in X-ray emission of cluster stars. In Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop (eds Donahue, R. A. & Bookbinder, J. A.) 501 (ASP Conference Series 154, Astronomical Society of the Pacific, 1998).

  44. Günther, M. N. et al. Stellar flares from the first TESS data release: exploring a new sample of M dwarfs. Astron. J. 159, 60 (2020).

    Article  ADS  Google Scholar 

  45. Ramsay, G., Doyle, J. G. & Doyle, L. TESS observations of southern ultrafast rotating low-mass stars. Mon. Not. R. Astron. Soc. 497, 2320–2326 (2020).

    Article  ADS  Google Scholar 

  46. Zhang, J. et al. Magnetic activity of F-, G-, and K-type stars in the LAMOST–Kepler field. Astrophys. J. Suppl. Ser. 247, 9 (2020).

    Article  ADS  Google Scholar 

  47. Gomes da Silva, J. et al. Stellar chromospheric activity of 1674 FGK stars from the AMBRE-HARPS sample. I. A catalogue of homogeneous chromospheric activity. Astron. Astrophys. 646, A77 (2021).

    Article  Google Scholar 

  48. Yu, J. et al. New evidence of binarity in young α-rich turn-off and subgiant stars: fast rotation and strong magnetic activity. Mon. Not. R. Astron. Soc. 530, 2953–2959 (2024).

    Article  ADS  Google Scholar 

  49. Marvin, C. J., Reiners, A., Anglada-Escudé, G., Jeffers, S. V. & Boro Saikia, S. Absolute Ca ii H & K and Hα flux measurements of low-mass stars: extending R′HK to M dwarfs. Astron. Astrophys. 671, A162 (2023).

    Article  ADS  Google Scholar 

  50. Karoff, C. et al. Observational evidence for enhanced magnetic activity of superflare stars. Nat. Commun. 7, 11058 (2016).

    Article  ADS  Google Scholar 

  51. Isaacson, H. & Fischer, D. Chromospheric activity and jitter measurements for 2630 stars on the California Planet Search. Astrophys. J. 725, 875–885 (2010).

    Article  ADS  Google Scholar 

  52. Boro Saikia, S. et al. Chromospheric activity catalogue of 4454 cool stars: questioning the active branch of stellar activity cycles. Astron. Astrophys. 616, A108 (2018).

    Article  Google Scholar 

  53. Isaacson, H. et al. The California–Kepler Survey. XI. A survey of chromospheric activity through the lens of precise stellar properties. Astrophys. J. 961, 85 (2024).

    Article  ADS  Google Scholar 

  54. Jeffers, S. V., Kiefer, R. & Metcalfe, T. S. Stellar activity cycles. Space Sci. Rev. 219, 54 (2023).

    Article  ADS  Google Scholar 

  55. LAMOST LRS stellar parameter catalog of A, F, G and K stars. The Data Release Nine of LAMOST Low-Resolution Spectroscopic Survey (LRS) section 3.2 (National Astronomical Observatories, Chinese Academy of Sciences, 2023); https://www.lamost.org/dr9/v2.0/doc/lr-data-production-description#S3.2

  56. Reinhold, T. et al. The Sun is less active than other solar-like stars. Science 368, 518–521 (2020).

    Article  ADS  Google Scholar 

  57. Zhang, J. et al. Solar-type stars observed by LAMOST and Kepler. Astrophys. J. Lett. 894, L11 (2020).

    Article  ADS  Google Scholar 

  58. Basri, G. & Shah, R. The information content in analytic spot models of broadband precision light curves. II. Spot distributions and lifetimes and global and differential rotation. Astrophys. J. 901, 14 (2020).

    Article  ADS  Google Scholar 

  59. Rutten, R. G. M. Magnetic structure in cool stars. VII. Absolute surface flux in Ca ii H and K line cores. Astron. Astrophys. 130, 353–360 (1984).

    ADS  Google Scholar 

  60. Hartmann, L., Soderblom, D. R., Noyes, R. W., Burnham, N. & Vaughan, A. H. An analysis of the Vaughan–Preston survey of chromospheric emission. Astrophys. J. 276, 254–265 (1984).

    Article  ADS  Google Scholar 

  61. Huang, Y. et al. Empirical metallicity-dependent calibrations of effective temperature against colours for dwarfs and giants based on interferometric data. Mon. Not. R. Astron. Soc. 454, 2863–2889 (2015).

    Article  ADS  Google Scholar 

  62. Huber, D. et al. Asteroseismology and Gaia: testing scaling relations using 2200 Kepler stars with TGAS parallaxes. Astrophys. J. 844, 102 (2017).

    Article  ADS  Google Scholar 

  63. Berger, T. A. et al. The Gaia–Kepler Stellar Properties Catalog. I. Homogeneous fundamental properties for 186,301 Kepler stars. Astron. J. 159, 280 (2020).

    Article  ADS  Google Scholar 

  64. Dotter, A. MESA Isochrones and Stellar Tracks (MIST) 0: methods for the construction of stellar isochrones. Astrophys. J. Suppl. Ser. 222, 8 (2016).

    Article  ADS  Google Scholar 

  65. Choi, J. et al. MESA Isochrones and Stellar Tracks (MIST). I. Solar-scaled models. Astrophys. J. 823, 102 (2016).

    Article  ADS  Google Scholar 

  66. Southworth, J. DEBCat: a catalog of detached eclipsing binary stars. In Living Together: Planets, Host Stars and Binaries (eds Rucinski, S. M. et al.) 164 (ASP Conference Series 496, Astronomical Society of the Pacific, 2015).

  67. Xiong, J. et al. The eclipsing binaries from the LAMOST Medium-Resolution Survey. III. A high-precision empirical stellar mass library. Astron. J. 165, 30 (2023).

    Article  ADS  Google Scholar 

  68. El-Badry, K. et al. Signatures of unresolved binaries in stellar spectra: implications for spectral fitting. Mon. Not. R. Astron. Soc. 473, 5043–5049 (2018).

    Article  ADS  Google Scholar 

  69. Eggleton, P. P. Approximations to the radii of Roche lobes. Astrophys. J. 268, 368–369 (1983).

    Article  ADS  Google Scholar 

  70. Pešta, M. & Pejcha, O. Mass-ratio distribution of contact binary stars. Astron. Astrophys. 672, A176 (2023).

    Article  ADS  Google Scholar 

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Acknowledgements

We thank J. Henneco, D. Huber, X. Wei, A. Shapiro, Z. Guo and T. Rozanski for discussions. We also acknowledge X.-S. Fang for providing data published in ref. 27. We extend our thanks to O. De Marco for helping us understand dynamo processes and for her exceptional facilitation of collaboration. J.Y. gratefully acknowledges the support provided by the entire TOS group at HITS, Heidelberg, during a three-month stay in 2023. J.Y., C.G., R.H.C. and L.G. acknowledge support from ERC Synergy Grant WHOLE SUN 810218. J.Y. and L.G. acknowledge PLATO grants from the German Aerospace Center (DLR 50OO1501) and from the Max Planck Society. We acknowledge funding from the ERC Consolidator Grant DipolarSound (grant agreement 101000296). Z.H. acknowledges support from the Natural Science Foundation of China (grant numbers 12288102). Y.-S.T. acknowledges financial support from the Australian Research Council through DECRA Fellowship DE220101520. J.N. acknowledges support from US National Science Foundation grants AST-2009713 and AST-2319326. S.B. and J.Y. acknowledge the Joint Research Fund in Astronomy (U2031203) under a cooperative agreement between the National Natural Science Foundation of China (NSFC) and the Chinese Academy of Sciences (CAS). This work has made use of data from the European Space Agency (ESA) mission Gaia (http://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; http://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions—in particular, the institutions participating in the Gaia Multilateral Agreement. Guoshoujing Telescope (LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciences. Funding for the project has been provided by the National Development and Reform Commission. LAMOST is operated and managed by the National Astronomical Observatories, Chinese Academy of Sciences.

Author information

Authors and Affiliations

  1. School of Computing, Australian National University, Canberra, Australian Capital Territory, Australia

    Jie Yu

  2. Research School of Astronomy & Astrophysics, Australian National University, Canberra, Australian Capital Territory, Australia

    Jie Yu

  3. Heidelberg Institute for Theoretical Studies (HITS) gGmbH, Heidelberg, Germany

    Jie Yu, Saskia Hekker & Michäel Bazot

  4. Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany

    Jie Yu, Charlotte Gehan, Robert H. Cameron, Yajie Chen & Laurent Gizon

  5. Centre for Astronomy (ZAH/LSW), Heidelberg University, Heidelberg, Germany

    Saskia Hekker

  6. Thüringer Landessternwarte, Tautenburg, Germany

    Patrick Gaulme

  7. Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, New South Wales, Australia

    Timothy R. Bedding

  8. Centre for Astrophysics, University of Southern Queensland, Toowoomba, Queensland, Australia

    Simon J. Murphy

  9. Yunnan Observatories, Chinese Academy of Sciences, Kunming, China

    Zhanwen Han

  10. International Centre of Supernovae, Yunnan Key Laboratory, Kunming, China

    Zhanwen Han

  11. Department of Astronomy, The Ohio State University, Columbus, OH, USA

    Yuan-Sen Ting

  12. Center for Cosmology and AstroParticle Physics (CCAPP), The Ohio State University, Columbus, OH, USA

    Yuan-Sen Ting

  13. Department of Astronomy, University of Florida, Bryant Space Science Center, Gainesville, FL, USA

    Jamie Tayar

  14. Institute for Astronomy, University of Hawai‘i, Honolulu, HI, USA

    Jamie Tayar

  15. Institut für Astrophysik, Georg-August-Universität Göttingen, Göttingen, Germany

    Laurent Gizon

  16. Center for Computational Relativity and Gravitation, Rochester Institute of Technology, Rochester, NY, USA

    Jason Nordhaus

  17. National Technical Institute for the Deaf, Rochester Institute of Technology, Rochester, NY, USA

    Jason Nordhaus

  18. School of Physics and Astronomy, Beijing Normal University, Beijing, China

    Shaolan Bi

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Contributions

J.Y. led the project, developed the data reduction package and conducted the primary analysis, interpretation and writing. C.G. proposed the S-index measurement methods using LAMOST spectra; C.G., Y.-S.T. and Y.C. analysed LAMOST spectra. S.H., R.H.C. and T.R.B. contributed to the design of the work. M.B., S.H. and R.H.C. helped in comprehending enhanced binary activity within the context of saturation for single main-sequence stars. J.Y. and Z.H. identified activity enhancements associated with common-envelope evolution. R.H.C., S.J.M., Z.H. and J.N. provided theoretical insights into dynamos. C.G. and P.G. helped understand the activity differences between dwarf and giant binary stars. S.H., R.H.C. and T.R.B. contributed to drafting the work. M.B., S.H., R.H.C., T.R.B. and S.J.M. facilitated collaboration. J.Y., C.G., M.B., S.H., R.H.C., P.G., T.R.B., S.J.M., Z.H., Y.-S.T., J.T., Y.C., L.G., J.N. and S.B. revised the draft.

Corresponding author

Correspondence to Jie Yu.

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Nature Astronomy thanks Antonio Frasca and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Validation of LAMOST stellar parameters using double-lined spectroscopic binaries.

Panels a, b, and c compare Teff, log g, and stellar masses obtained from the LAMOST DR9v2.0 Stellar Parameters Catalog with literature values66,67 for the primary stars in SB2 systems. LAMOST Teff and log g values (vertical axes) were obtained from single-star atmospheric models applied to LAMOST spectra. Stellar masses were determined by isochrone fitting using isoclassify, with LAMOST Teff, log g, and [Fe/H] as input constraints (see Methods for details). Error bars in each panel represent the 1-σ uncertainties. Along the three horizontal axes, the Teff values for the primary stars obtained from the literature studies are estimated from spectra observed near the secondary minimum eclipses to minimise flux contamination from companions. The mass values are dynamical masses of SB2 stars derived from radial velocities and light curves, while the log g values are calculated from the dynamical masses and radii of SB2 binaries. These comparisons show an offset of 9 K with a standard deviation of 304 K for Teff, 0.00 dex with a standard deviation of 0.12 dex for log g, and 0.03 M⊙ with a standard deviation of 0.20 M⊙ for mass. The black dashed line in each panel represents the one-to-one relation, while the dashed-dotted lines indicate offsets of 200 K for Teff, 0.12 dex for log g, and 0.2 M⊙ for mass.

Extended Data Fig. 2 Calibration of the SHK index.

The calibration sample consists of 273 stars brighter than 13th magnitude in the Gaia G-band (circles in both panels), for which the SHK index values on the Mount Wilson scale (SHK,MW) are available from the literature47,51,52,53. We performed an iterative linear fitting by rejecting 3-σ outliers (11 stars removed, 1 iteration after convergence). The resulting best fit is presented with the black dashed line: SHK,MW =(5.132 ± 0.276) × SHK,LAMOST - (0.865 ± 0.066), where SHK,LAMOST represents the SHK index measurements from our work. The 1-σ formal uncertainties of the calibrated SHK values are shown as error bars in both panels. The faint stars (G > 13, squares shown in the left panel), which were not included in the calibration, contribute to the large scatter observed at low SHK,LAMOST values. This is expected, as the spectra of stars with small SHK values are more likely to be affected by noise. The left panel highlights the literature subsamples used for the calibration, while the right panel is color-coded by the Teff range of the calibration sample, with Teff values obtained from LAMOST DR9.

Extended Data Fig. 3 Comparison of rotation periods (Prot) and orbital periods (Prot) for 1,407 main-sequence and subgiant stars.

This sample includes Kepler eclipsing binaries15 and Gaia binaries10, whose rotation periods are available from previous studies23,24,25 based on Kepler and K225 light curves. The purple shading indicates the region where the Prot/Porb ratio falls between 1:2 and 2:1, while the blue shading highlights the region where the Prot/Porb ratio is between 2:1 and 3:1, or between 1:3 and 1:2. The diagonal dashed line represents a one-to-one correspondence. The vertical dashed line at P = 30 days signifies a boundary beyond which binaries are almost not synchronised. We categorise the systems to the left as close binaries and those to the right as wide binaries.

Extended Data Fig. 4 Chromospheric activity of close and wide Gaia binary systems.

The SHK,LAMOST values are measured from the Ca II H & K lines in LAMOST spectra and expressed as the SHK index on the LAMOST scale. The vertical dashed line at P = 30 days serves as a boundary distinguishing the regime where the SHK index depends on the orbital period (Porb ≲ 30 days) from the regime where it does not (Porb ≳ 30 days). The red symbols depict the median SHK indexes of orbital period bins of \(\Delta \log P=0.2\), while the error bars indicate five times the standard errors. A linear fit to the median values of the close binaries is illustrated with an orange dashed line. The error bar in the lower left corner indicates the median uncertainty of the SHK index measurements for the entire sample, measured at ~ 0.01.

Extended Data Fig. 5 Five example LAMOST low-resolution spectra around the Ca II H & K lines.

The wavelengths are shifted to the rest frame using radial velocities derived from this study. The upper panel compares the spectra of a single star and a binary star in the saturated regime, with comparable rotation and orbital periods of 0.53 days. The lower panel presents the spectra of three binary stars in the supersaturated, saturated, and unsaturated regimes, with orbital periods of 0.29, 0.53, and 5.95 days, respectively. Among the four unique stars shown (the binary star in the saturated regime appears in both panels), all have similar Teff (6227–6374 K) and log g (4.25–4.32) values adopted from the LAMOST LRS Stellar Parameter Catalog. The LAMOST obsid of each spectrum is annotated in the figure. These four stars are marked with green asterisks in Fig. 2.

Supplementary information

Supplementary Information

Supplementary Fig. 1 and References.

Supplementary Data 1

Data used in Figs. 1–4, Extended Data Fig. 2 and Supplementary Fig. 1.

Supplementary Data 2

Data used in Fig. 2 and Supplementary Fig. 1.

Supplementary Data 3

Data used in Fig. 2 and Supplementary Fig. 1.

Supplementary Data 4

Data used in Extended Data Fig. 1.

Supplementary Data 5

Data used in Extended Data Fig. 1.

Supplementary Data 6

Data used in Extended Data Fig. 1.

Supplementary Data 7

Data used in Extended Data Figs. 3 and 4.

Supplementary Data 8

Data used in Extended Data Fig. 5.

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Yu, J., Gehan, C., Hekker, S. et al. Enhanced magnetic activity in rapidly rotating binary stars. Nat Astron (2025). https://doi.org/10.1038/s41550-025-02562-2

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