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X-ray emission from nearby M-dwarfs: the super-saturation phenomenon

James, David J. ; Jardine, Moira M. ; Jeffries, Robin D. ; Randich, Sofia ; Collier Cameron, Andrew ; Ferreira, Miguel

In: Monthly Notices of the Royal Astronomical Society, 2000, vol. 318, no. 4, p. 1217-1226

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    Titre
    • X-ray emission from nearby M-dwarfs: the super-saturation phenomenon
    Auteur
    • James, David J.. School of Physics and Astronomy, North Haugh, University of St Andrews, St Andrews, Fife KY16 9SS
    • Jardine, Moira M.. School of Physics and Astronomy, North Haugh, University of St Andrews, St Andrews, Fife KY16 9SS
    • Jeffries, Robin D.. Department of Physics, Keele University, Keele, Staffordshire ST5 5BG
    • Randich, Sofia. Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
    • Collier Cameron, Andrew. School of Physics and Astronomy, North Haugh, University of St Andrews, St Andrews, Fife KY16 9SS
    • Ferreira, Miguel. School of Physics and Astronomy, North Haugh, University of St Andrews, St Andrews, Fife KY16 9SS
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Monthly Notices of the Royal Astronomical Society, 2000, vol. 318, no. 4, p. 1217-1226. Blackwell Science Ltd
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:290207
    Summary
    A rotation rate and X-ray luminosity analysis is presented for rapidly rotating single and binary M-dwarf systems. X-ray luminosities for the majority of both single and binary M-dwarf systems with periods below ≃5-6 d (equatorial velocities, Veq≳6 km s−1) are consistent with the current rotation-activity paradigm, and appear to saturate at about 10−3 of the stellar bolometric luminosity. The single M-dwarf data show tentative evidence for the super-saturation phenomenon observed in some ultra-fast rotating (≳100 km s−1) G- and K-dwarfs in the IC 2391, IC 2602 and Alpha Persei clusters. The IC 2391 M star VXR60b is the least X-ray active and most rapidly rotating of the short period (Prot≲2 d) stars considered herein, with a period of 0.212 d and an X-ray activity level of about 1.5 sigma below the mean X-ray emission level for most of the single M-dwarf sample. For this star, and possibly one other, we cautiously believe that we have identified the first evidence of super-saturation in M-dwarfs. If we are wrong, we demonstrate that only M-dwarfs rotating close to their break-up velocities are likely to exhibit the super-saturation effect at X-ray wavelengths. The M-dwarf X-ray data also show that there is no evidence for any difference in the X-ray behaviour between the single and binary systems, because for the single stars, the mean log LxLbol=−3.21±0.04 (0.2≲Prot≲10.1 d), whereas for the binary stars, the mean log LxLbol=−3.19±0.10 (0.8≲Prot≲10.4 d). Furthermore, we show that extremely X-ray active M-dwarfs exhibit a blue excess of about 0.1 magnitudes in U-B compared with less active field M-dwarfs. Such an excess level is comparable to that observed for extremely chromospherically active M-dwarfs. Moreover, as is the case for M-dwarf Ca ii H and K activity levels, there is an exclusion zone of X-ray activity between the extremely active M-dwarfs and the less active ones