The triple system AT Mic AB + AU Mic in the beta Pictoris Association

Abstract

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. 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 analysed the triple system AU Mic + AT Mic A&B in the 25-Myr beta Pictoris Association. We have retrieved from the literature the rotation period of AU Mic (P = 4.85d) and measured from photometric archival data the rotation periods of both components of AT Mic (P = 1.19d and P = 0.78d) 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 about 27 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 (about 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 about 7.3 x 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.

References in corpus (9)

• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• The first WASP public data release
• The Factory and The Beehive II. Activity and Rotation in Praesepe and the Hyades
• Accretion Disks around Young Stars: Lifetimes, Disk Locking and Variability
• Gas and dust in the Beta Pictoris Moving Group as seen by the Herschel Space Observatory
• Nearby young stars selected by proper motion. I. Four new members of the Beta Pictoris moving group from the Tycho-2 catalog
• Rotation and activity of pre-main-sequence stars
• The evolution of accretion in young stellar objects: Strong accretors at 3 - 10 Myr
• A Search for Planets Transiting the M Dwarf Debris Disk Host, AU Microscopii

Cited by in corpus (2)

• The beta Pictoris association: Catalog of photometric rotational periods of low-mass members and candidate members
• X-Ray and Ultraviolet Flares on AT Microscopii Observed by AstroSat