Astrophysics and Space Science

, 361:291 | Cite as

The triple system AT Mic AB + AU Mic in the \(\beta \) Pictoris association

  • Sergio MessinaEmail author
  • Giuseppe Leto
  • Isabella Pagano
Original Article


Equal-mass stars in young open clusters and loose associations exhibit a wide spread of rotation periods, which likely originates from differences in the initial rotation periods and in the primordial disc lifetimes. We want to explore if the gravitational effects by nearby companions may play an additional role in producing the observed rotation period spread, as well as, the role that magnetic activity may also play. We measure the photometric rotation periods of components of multiple stellar systems and look for correlations of the period differences among the components to their reciprocal distances. In this paper, we analyzed the triple system AU Mic + AT Mic A&B in the \(25\pm 3\)-Myr \(\beta \) Pictoris association. We have retrieved from the literature the rotation period of AU Mic (\({P} = 4.85~\mbox{d}\)) and measured from photometric archival data the rotation periods of both components of AT Mic (\({P} = 1.19~\mbox{d}\) and \({P} = 0.78~\mbox{d}\)) for the first time. Moreover, we detected a high rate of flare events from AT Mic. Whereas the distant component AU Mic has evolved rotationally as a single star, the A and B components of AT Mic, separated by \(\sim 27~\mbox{AU}\), exhibit a rotation rate a factor 5 larger than AU Mic. Moreover, the A and B components, despite have about equal mass, show a significant difference (\(\sim 40~\%\)) between their rotation periods. A possible explanation is that the gravitational forces between the A and B components of AT Mic (that are a factor \(\sim 7.3\times 10^{6}\) more intense than those between AU Mic and AT Mic) have enhanced the dispersal of the AT Mic primordial disc, shortening its lifetime and the disc-locking phase duration, making the component A and B of AT Mic to rotate faster than the more distant AU Mic. We suspect that a different level of magnetic activity between the A and B components of AT Mic may be the additional parameter responsible for the difference between their rotation periods.


Stars: activity Stars: late-type Stars: rotation Stars: starspots Stars: abundances Stars: individual: AU Mic, AT Mic, \(\beta \) Pictoris association 



Research on stellar activity at INAF—Catania Astrophysical Observatory is supported by MIUR (Ministero dell’Istruzione, dell’Università e della Ricerca). This paper makes use of data from the first public release of the WASP data (Butters et al. 2010) as provided by the WASP consortium and services at the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. This research has made use of the Simbad database, operated at CDS (Strasbourg, France). We thank the anonymous Referee for useful comments that allowed us to improve the paper quality.


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Copyright information

© Springer Science+Business Media Dordrecht 2016

Authors and Affiliations

  1. 1.INAF—Catania Astrophysical ObservatoryCataniaItaly

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