2019ApJ...870...74S

We report the timing results for PSR J2234+0611, a 3.6 ms pulsar in a 32 day, eccentric (e = 0.13) orbit with a helium white dwarf. The precise timing and eccentric nature of the orbit allow measurements of an unusual number of parameters: (a) a precise proper motion of 27.10(3) mas yr^–1 and a parallax of 1.05(4) mas resulting in a pulsar distance of 0.95(4) kpc; enabling an estimate of the transverse velocity, 123(5) km s^–1. Together with previously published spectroscopic measurements of the systemic radial velocity, this allows a 3D determination of the system's velocity; (b) precise measurements of the rate of advance of periastron yields a total system mass of 1.6518_–0.0035^+0.0033M_☉; (c) a Shapiro delay measurement, h₃ = 82 ± 14 ns, despite the orbital inclination not being near 90°; combined with the measurement of the total mass yields a pulsar mass of 1.353_–0.017^+0.014M_☉ and a companion mass of 0.298_–0.012^+0.015M_☉; (d) we measure precisely the secular variation of the projected semimajor axis and detect a significant annual orbital parallax; together these allow a determination of the 3D orbital geometry of the system, including an unambiguous orbital inclination (i=138.7_–2.2^+2.5°) and a position angle for the line of nodes (Ω=44_–4⁺⁵°). We discuss the component masses to investigate the hypotheses previously advanced to explain the origin of eccentric MSPs. The unprecedented determination of the 3D position, motion, and orbital orientation of the system, plus the precise pulsar and WD masses and the latter's optical detection make this system a unique test of our understanding of white dwarfs and their atmospheres.