OK, I'm making up a fictional planet (this is something of a follow up to my earlier thread). The planet is supposed to orbit Alpha Centauri B at .72-.73 AU, be about .76 Earth masses, and have an Earthlike moon.
According to this paper the stability region for satellites of a planet is .48 times the Hill sphere for prograde orbits. This Hill sphere calculator gives a Hill sphere of roughly 1 million km for my planet, which should translate into a stability region of ~480,000 km. So going by that an Earthlike moon should be fine.
However, I tried simulating the arrangement with Gravity Simulator and I got a highly unstable orbit.
I'm inclined to trust the paper (it does focus on gas giant satellites but I don't see why this situation should essentially be any different), but my knowledge of orbital mechanics is nonexistant. Does anybody who knows more about the subject have any advice on this?