2004A&A...426..631L

We present results of high-precision timing measurements of the binary millisecond pulsar PSR J2145-0750. Combining 10 yrs of radio timing data obtained with the Effelsberg 100-m radio telescope and the Lovell 76-m radio telescope we measure a significant timing parallax of 2.0(6)mas placing the system at 500 pc distance to the solar system. The detected secular change of the projected semi-major axis of the orbit {dot}(x=1.8(6))x10^–14lt-s/s, where x=(a_psini)/c, is caused by the proper motion of the system. With this measurement we can constrain the orbital inclination angle to i<61°, with a median likelihood value of 46° which is consistent with results from polarimetric studies of the pulsar magnetosphere. This constraint together with the non-detection of Shapiro delay rules out certain combinations of the companion mass, m₂, and the inclination, i. For typical neutron star masses and using optical observations of the carbon/oxygen-core white dwarf we derive a mass range for the companion of 0.7M_☉≤m₂≤1.0M_☉. We apply evolutionary white dwarf cooling models to revisit the cooling age of the companion. Our analysis reveals that the companion has an effective temperature of T_ eff_=5750±600K and a cooling age of τ_ cool_=3.6(2)Gyr, which is roughly a factor of three lower than the pulsar's characteristic age of 10.4Gyr. The cooling age implies an initial spin period of P₀=13.0(5)ms, which is very close to the current period.