Wind Accretion vs. Roche Lobe Overflow in HMXBs

We note there are two distinct classes of high mass X-ray binary:

  Disk Fed Wind Fed
$P_{\rm orb}$ short long
$P_{\rm pulse}$ short long
$\dot P_{\rm pulse}$ steady random
$L_x$ high low

Object $P_{\rm orb}\ {\rm (days)}$ $P_{\rm pulse}\ {\rm (sec)}$ $\dot \nu\ {\rm (10^{-13}\ Hz\ sec^{-1})}$ $L_x\ {\rm (erg\sec^{-1})}$ Type
LMC X-4 1.4 13.5 -- $4\times10^{38}$ Disk
Cen X-3 2.1 4.8 65.7 $8\times10^{37}$ Disk
SMC X-1 3.9 0.7 233 $3\times10^{38}$ Disk
OAO 1657-415 10.4 37.7 55.8 $3\times10^{36}$ Wind
Vela X-1 9.0 283 1.2 $6\times10^{36}$ Wind



Why the sharp distinction?