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.
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