Random thought - I recall somewhere that Merope 5c's orbit inclination is 138 degrees? Even thought I've honked the Merope system several times since I started playing for some reason 5c isn't showing so I can't confirm...
The line that extends diagonally down/right happens to be more or less bang on 138 degrees clockwise from the top of the circle.
Nope, the orbital inclination is ~75 degrees. 138 degrees is the longitude of periapsis, i.e. what point in it's orbit it is closest to the star.
Given that M5C is an almost perfectly circular orbit (0.00000 I think) this point is fairly arbitrary.
Speaking of orbital mechanics, people have been talking a bit about tidal locking, but even though M5c is tidally locked to M5, given that there is an axial tilt of some 15 degrees, I suspect that M5 does move in the sky of M5c, oscillating back and forth by 30 degrees each "year/day". I'm not sure at what orbital phase the rotational axis lies in the plane of the orbit, as I don't think this info is in the system map.