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Optical flares and flaring oscillations on the M-type eclipsing binary CU Cancri

Authors

  • S.-B. Qian,

    Corresponding author
    1. National Astronomical Observatories/Yunnan Astronomical Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    2. Key Laboratory of the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    3. Graduate University of the Chinese Academy of Sciences, Yuquan Road 19, Sijingshang Block, 100049 Beijing City, China
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  • J. Zhang,

    1. National Astronomical Observatories/Yunnan Astronomical Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    2. Key Laboratory of the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    3. Graduate University of the Chinese Academy of Sciences, Yuquan Road 19, Sijingshang Block, 100049 Beijing City, China
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  • L.-Y. Zhu,

    1. National Astronomical Observatories/Yunnan Astronomical Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    2. Key Laboratory of the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
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  • L. Liu,

    1. National Astronomical Observatories/Yunnan Astronomical Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    2. Key Laboratory of the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
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  • W.-P. Liao,

    1. National Astronomical Observatories/Yunnan Astronomical Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    2. Key Laboratory of the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
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  • E.-G. Zhao,

    1. National Astronomical Observatories/Yunnan Astronomical Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    2. Key Laboratory of the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
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  • J.-J. He,

    1. National Astronomical Observatories/Yunnan Astronomical Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    2. Key Laboratory of the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
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  • L.-J. Li,

    1. National Astronomical Observatories/Yunnan Astronomical Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    2. Key Laboratory of the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    3. Graduate University of the Chinese Academy of Sciences, Yuquan Road 19, Sijingshang Block, 100049 Beijing City, China
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  • K. Li,

    1. National Astronomical Observatories/Yunnan Astronomical Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    2. Key Laboratory of the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    3. Graduate University of the Chinese Academy of Sciences, Yuquan Road 19, Sijingshang Block, 100049 Beijing City, China
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  • Z.-B. Dai

    1. National Astronomical Observatories/Yunnan Astronomical Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
    2. Key Laboratory of the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China
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E-mail: qsb@ynao.ac.cn

ABSTRACT

In this paper, we report on the discovery of an optical flare observed in the R band from the red-dwarf eclipsing binary CU Cancri, whose component stars are at the upper boundary of full convection (M1= 0.43 M and M2= 0.4 M, where M is the solar mass). The amplitude of the flare is the largest among those detected in the R band (∼0.52 mag) and the duration time is about 73 min. Like flares observed on the Sun, quasi-periodic oscillations were seen during and after the flare. Three more R-band flares were found by follow-up monitoring. In total, this binary was monitored photometrically by using an R filter for 79.9 h, which has revealed an R-band flare rate of about 0.05 flares per hour. Together with other strong chromospheric and coronal activities (i.e. very strong Hα and Hβ emission features and an extreme ultraviolet and X-ray source), these detections indicate that it has very strong magnetic activity. Therefore, the apparent faintness (∼1.4 mag in the V band) of CU Cnc, compared with other single red dwarfs of the same mass, can be plausibly explained by the high coverage of dark spots.

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