  We report on the main results obtained thanks to an observation campaign with
XMM-Newton of four persistent, low-luminosity (Lx ~ 10^34 erg/s) and
long-period (P > 200 s) Be accreting pulsars. We found that all sources
considered here are characterized by a spectral excess that can be described
with a blackbody component of high temperature (kTbb > 1 keV) and small area
(Rbb < 0.5 km). We show that: 1) this feature is a common property of several
low-luminosity X-ray binaries; 2) for most sources the blackbody parameters
(radius and temperature) are within a narrow range of values; 3) it can be
interpreted as emission from the NS polar caps.
