Four ultra-short-period eclipsing M-dwarf binaries in the WFCAM Transit Survey

S. V. Nefs, J. L. Birkby, I. A G Snellen, S. T. Hodgkin, D. J. Pinfield, B. Sipocz, G. Kovacs, Dimitrios Mislis, R. P. Saglia, J. Koppenhoefer, P. Cruz, D. Barrado, E. L. Martin, N. Goulding, H. Stoev, J. Zendejas, C. del Burgo, M. Cappetta, Y. V. Pavlenko

Research output: Contribution to journalArticle

38 Citations (Scopus)


We report on the discovery of four ultra-short-period (P ≤ 0.18d) eclipsing M-dwarf binaries in the Wide-Field Camera (WFCAM) Transit Survey. Their orbital periods are significantly shorter than that of any other known main-sequence binary system, and are all significantly below the sharp period cut-off at P ∼ 0.22 d as seen in binaries of earlier-type stars. The shortest-period binary consists of two M4-type stars in a P = 0.112 d orbit. The binaries are discovered as part of an extensive search for short-period eclipsing systems in over 260000 stellar light curves, including over 10000 M-dwarfs down to J = 18mag, yielding 25 binaries with P ≤ 0.23d. In a popular paradigm, the evolution of short-period binaries of cool main-sequence stars is driven by the loss of angular momentum through magnetized winds. In this scheme, the observed P ∼ 0.22d period cut-off is explained as being due to time-scales that are too long for lower-mass binaries to decay into tighter orbits. Our discovery of low-mass binaries with significantly shorter orbits implies that either these time-scales have been overestimated for M-dwarfs, e.g. due to a higher effective magnetic activity, or the mechanism for forming these tight M-dwarf binaries is different from that of earlier-type main-sequence stars.

Original languageEnglish
Pages (from-to)950-968
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - 11 Sep 2012
Externally publishedYes



  • Binaries: eclipsing
  • Stars: low-mass

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Nefs, S. V., Birkby, J. L., Snellen, I. A. G., Hodgkin, S. T., Pinfield, D. J., Sipocz, B., Kovacs, G., Mislis, D., Saglia, R. P., Koppenhoefer, J., Cruz, P., Barrado, D., Martin, E. L., Goulding, N., Stoev, H., Zendejas, J., del Burgo, C., Cappetta, M., & Pavlenko, Y. V. (2012). Four ultra-short-period eclipsing M-dwarf binaries in the WFCAM Transit Survey. Monthly Notices of the Royal Astronomical Society, 425(2), 950-968.