Paper detail

Physical parameters and long-term photometric variability of V1481 Ori, a SB2 member of Orion Nebula Cluster with an accreting component

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.