CARMENES obs. of the binary system LB-1

We conducted a high-resolution, phase-resolved spectroscopic study of its Paschen lines, using the Calar Alto 3.5m telescope. We find that Pa{beta} and Pa{gamma} (after subtraction of the stellar absorption component) are well fitted with a standard double-peaked disk profile.

We measured the velocity shifts of the red and blue peaks at 28 orbital phases: the line center has an orbital motion in perfect antiphase with the secondary, and the radial velocity amplitude ranges from 8 to 13km/s, for different methods of profile modeling. We interpret this curve as proof that the disk traces the orbital motion of the primary, ruling out the circumbinary disk and the hierarchical triple scenarios. The phase-averaged peak-to-peak half-separation (a proxy for the projected rotational velocity of the outer part of the disk) is ~70km/s, larger than the orbital velocity of the secondary and inconsistent with a circumbinary disk.