  We present the results of our analysis on V1481 Ori (JW 239), a young SB2 in
the Orion Nebula Cluster with a circumbinary disc accreting on the lower-mass
component. The analysis is based on high-resolution spectroscopic data and
high-quality photometric time series about 20-yr long. Thanks to the
spectroscopy, we confirm the binary nature of this system consisting of M3 + M4
components and derive the mass ratio M_B/M_A = 0.54, a variable luminosity
ratio L_B/L_A = 0.68--0.94, and an orbital period P_orb = 4.433d. The
photometric data allowed us to measure the rotation periods of the two
components P_phot = 4.4351d and they are found to be synchronized with the
orbital period. The simultaneous modeling of V-, I-band, and radial velocity
curves in the 2005 season suggests that the variability is dominated by one hot
spot on the secondary component covering at least about 3.5% of the stellar
surface and about 420K hotter than the unperturbed photosphere. Such a spot may
originate from the material of the circumbinary disc accreting onto the
secondary component. We also detect an apparent 6-yr periodic variation in the
position of this hot spot, which is inferred from the phase migration of the
light curve maximum, which we interpret as due to either the presence of
surface differential rotation as large as 0.065%, a value compatible with the
fully convective components, or to a periodic exchange of angular momentum
between the disc and the star, which implies a minimum magnetic field strength
of 650G at the stellar surface.

Solar and Stellar Astrophysics