About accretion disk of a binary system

[jtceleron]

In an X-ray binary system, in which one of the two objects is black hole candidate, there are several ways to exchange mass.
A paper states that" their host systems are mass-exchange binaries containing a nondegenerate star that supplies gas to the black hole via a stellar wind or via Roche-lobe overflow in a stream that emanates from the inner Lagrangian point. The mass-donor star in the Roche-lobe overflow systems is typically a low mass (~one sun mass) sun-like star, and the X-ray source is transient, alternating between yearlong outbursts and years or decades of quiescence. the wind-fed X-ray source, on the other hand, are fueled by massive hot stars( larger than 10 times of sun mass) and are persistently luminous."

I wonder why the Roche-lobe overflow has a period while the other mechanism has not.

 

[mfb]

Wind is continuous, as long as the star itself is not variable.
For Roche-lobe overflow, I have to guess: The material can interact with itself, this might generate bunches in some way.

 

[jtceleron]

Wind is continuous, as long as the star itself is not variable.
For Roche-lobe overflow, I have to guess: The material can interact with itself, this might generate bunches in some way.

what is the difference of the two in mechanism? Does the period of luminosity relate to the period of orbit of the companion star? but if so, why does the stellar wind one not have a period of luminosity.

 

[mfb]

Years or even decades is longer than orbital periods if Roche-lobe overflow is relevant.
Maybe you can have some mass accretion near the lagrange points.