  We report on the main results obtained thanks to an observation campaign,
performed 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 (kT > 1 keV) and small
area (R < 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.
