A New Look at Distances and Velocities of Neutron Stars

Abstract

Abstract. We take a fresh look at the determination of distances and velocities of neutron stars. The conversion of a parallax measurement into a distance, or distance probability distribution, has led to a debate quite similar to the one involving Cepheids, centering on the question whether priors can be used when discussing a single system. With the example of PSR J0218+4232, we show that a prior is necessary to determine the probability distribution for the distance. The distance of this pulsar implies a gamma-ray luminosity larger than 10% of its spindown luminosity. For velocities, the debate is whether a single Maxwellian describes the distribution for young pulsars. By limiting our discussion to accurate (VLBI) measurements we argue that a description with two Maxwellians, with distribution parameters σ 1 = 77 and σ 2 = 320 km/s, is significantly better. Corrections for galactic rotation, to derive velocities with respect to the local standards of rest, are insignificant.

Magnetic White Dwarfs

“…At long orbital periods ( 3 h) magnetic braking (Verbunt and Zwaan 1981;Rappaport et al 1983) acts as main mechanism that ceases at ∼3 h when secondaries become fully convective and shrink within their Roche lobe. Mass transfer stops until contact is re-established near ∼2 h. This gives rise to the so-called 2-3 h CV orbital period gap (Rappaport et al 1983;Spruit and Ritter 1983;Davis et al 2008).…”

Discovery of a Candidate Black Hole - Giant Star Binary System in the Galactic Field

“…The shape, character, and phasing of the lightcurve are inconsistent with stellar pulsations or ellipsoidal variations, but are typical of the class of spotted K giants like HD 1833, V1192 Orionis, and KU Pegasi (24,25). Such systems in binaries with periods less than ∼ 150 days often have low eccentricities, implying rapid tidal circularization (26)(27)(28). The change in the shape of the lightcurve over time shown in Figure 1 likely indicates spot evolution.…”

Dark passengers★ in stellar surveys

“…Early observations suggested that neutron stars receive natal kicks, and that the velocity is distributed according to a Gaussian with zero mean and a dispersion of about 260 km s −1 (Hobbs et al 2005). Newer observations suggest there might be another population of neutron stars, of which the kick velocities follow a double peaked Gaussian distribution but with smaller dispersions of just 77 km s −1 for 0.42 of the systems and 320 km s −1 for the rest (Verbunt & Cator 2017). Double neutron star binaries exhibit a somewhat similar doubly peaked kick distribution, with roughly two thirds of the systems experiencing kicks lower than 30 km s −1 and others exhibiting larger kicks, consistent with the regular neutron star population (Beniamini & Piran 2016;Tauris et al 2017).…”