Abstract:
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
=
4.433 d. The photometric data allowed us
to measure the rotation periods of the two components
P
phot
=
4.4351 d and they are found
to be synchronized with the orbital period. The simultaneous modelling of
V
-,
I
-band, and
radial velocity curves in the 2005 season suggests that the variability is dominated by one
hotspot on the secondary component covering at least
∼
3.5 per cent of the stellar surface and
about 420 K hotter than the unperturbed photosphere. Such a spot may originate from the
material of the circumbinary disc accreting on to the secondary component. We also detect
an apparent 6-yr periodic variation in the position of this hotspot, 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 per cent, 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 650 G at the stellar surface.
