  While the distribution of spin periods of High Mass X-ray Binaries (HMXBs)
spans more than four orders of magnitude (69ms - 25min), the few known X-ray
pulsars accreting from very low mass companions (<1 Msun) have very similar
periods between 5.4 and 8.7s . These pulsars display also several other
similarities and they are probably members of a subclass of Low Mass X-ray
Binaries (LMXBs) with similar magnetic field (a few 10^11 G), companion stars
and, possibly, evolutionary histories. If they are rotating at, or close to,
the equilibrium period, their properties are consistent with luminosities of
the order of a few 10^35 erg/s. These pulsars might represent the closest
members of a subclass of LMXBs characterized by lower luminosities, higher
magnetic fields and smaller ages than non-pulsating LMXBs.
