We report on the discovery of the companion star to the millisecond pulsar J1342+2822B in the globular cluster M3 .
We exploited a combination of near-ultraviolet and optical observations acquired with the Hubble Space Telescope in order to search for the optical counterparts to the known millisecond pulsars in this cluster .
At a position in excellent agreement with that of the radio pulsar J1342 + 2822B ( M3B ) , we have identified a blue and faint object ( m _ { F 275 W } \approx 22.45 ) that , in the color-magnitude diagram of the cluster , is located in the region of He core white dwarfs .
From the comparison of the observed magnitudes with theoretical cooling tracks we have estimated the physical properties of the companion star : it has a mass of only 0.19 \pm 0.02 M _ { \odot } , a surface temperature of 12 \pm 1 \cdot 10 ^ { 3 } K and a cooling age of 1.0 ^ { +0.2 } _ { -0.3 } Gyr .
Its progenitor was likely a \sim 0.84 M _ { \odot } star and the bulk of the mass-transfer activity occurred during the sub-giant branch phase .
The companion mass , combined with the pulsar mass function , implies that this system is observed almost edge-on and that the neutron star has a mass of 1.1 \pm 0.3 M _ { \odot } , in agreement with the typical values measured for recycled neutron stars in these compact binary systems .
We have also identified a candidate counterpart to the wide and eccentric binary millisecond pulsar J1342+2822D .
It is another white dwarf with a He core and a mass of 0.22 \pm 0.2 M _ { \odot } , implying that the system is observed at a high inclination angle and hosts a typical NS with a mass of 1.3 \pm 0.3 M _ { \odot } .
At the moment , the large uncertainty on the radio position of this millisecond pulsar prevents us from robustly concluding that the detected star is its optical counterpart .