Neutron stars in low-mass X-ray binaries are considered promising candidate sources of continuous gravitational-waves. These neutron stars are typically rotating many hundreds of times a second. The process of accretion can potentially generate and support non-axisymmetric distortions to the compact object, resulting in persistent emission of gravitational-waves. We present a study of existing optical spectroscopic data for Sco X-1, a prime target for continuous gravitational-wave searches, with the aim of providing revised constraints on key orbital parameters required for a directed search with advanced-LIGO data. From a circular orbit fit to an improved radial velocity curve of the Bowen emission components, we derived an updated orbital period and ephemeris. Centre of symmetry measurements from the Bowen Doppler tomogram yield a centre of the disc component of 90 km s −1 , which we interpret as a revised upper limit to the projected orbital velocity of the NS K 1 . By implementing Monte Carlo binary parameter calculations, and imposing new limits on K 1 and the rotational broadening, we obtained a complete set of dynamical system parameter constraints including a new range for K 1 of 40-90 km s −1 . Finally, we discussed the implications of the updated orbital parameters for future continuous-waves searches.

We present phase-resolved spectroscopy of the millisecond X-ray pulsar XTE J1814-338 obtained during its 2003 outburst. The spectra are dominated by high-excitation emission lines of He ii λ4686, Hβ, and the Bowen blend C iii/N iii 4630-50Å. We exploit the proven Bowen fluorescence technique to establish a complete set of dynamical system parameter constraints using bootstrap Doppler tomography, a first for an accreting millisecond X-ray pulsar binary. The reconstructed Doppler map of the N iii λ4640 Bowen transition exhibits a statistically significant (> 4σ) spot feature at the expected position of the companion star. If this feature is driven by irradiation of the surface of the Roche lobe filling companion, we derive a strict lower limit to the true radial velocity semi-amplitude K 2 . Combining our donor constraint with the well constrained orbit of the neutron star leads to a determination of the binary mass ratio: q = 0.123 +0.012−0.010 . The component masses are not tightly constrained given our lack of knowledge of the binary inclination. We cannot rule out a canonical neutron star mass of 1.4 M (1.1 M < M 1 < 3.1 M ; 95%). The 68/95% confidence limits of M 2 are consistent with the companion being a significantly bloated, M-type main sequence star. Our findings, combined with results from studies of the quiescent optical counterpart of XTE J1814-338, suggest the presence of a rotation-powered millisecond pulsar in XTE J1814-338 during an X-ray quiescent state. The companion mass is typical of the so-called 'redback' pulsar binary systems (M 2 ∼ 0.2 M ).

AM CVn binaries are a class of ultracompact, hydrogen-deficient binaries, each consisting of a white dwarf accreting helium-dominated material from a degenerate or semi-degenerate donor star. Of the 56 known systems, only Gaia14aae undergoes complete eclipses of its central white dwarf, allowing the parameters of its stellar components to be tightly constrained. Here, we present phase-resolved optical spectroscopy of Gaia14aae. We use the spectra to test the assumption that the narrow emission feature known as the 'central spike' traces the motion of the central white dwarf. We measure a central spike velocity amplitude of 13.8 ± 3.2 km/s, which agrees at the 1 σ level with the predicted value of 17.6 ± 1.0 km/s based on eclipse-derived system parameters. The orbital phase offset of the central spike from its expected position is 4 ± 15 • , consistent with 0 • . Doppler maps of the He i lines in Gaia14aae show two accretion disc bright spots, as seen in many AM CVn systems. The formation mechanism for the second spot remains unclear. We detect no hydrogen in the system, but we estimate a 3 σ limit on Hα emission with an equivalent width of -1.14Å. Our detection of nitrogen and oxygen with no corresponding detection of carbon, in conjunction with evidence from recent studies, mildly favours a formation channel in which Gaia14aae is descended from a cataclysmic variable with a significantly evolved donor. Parameter Value Mass ratio, q 0.0287(20) Inclination, i ( • ) 86.3(3) Orbital separation, a (R ) 0.430(3) Accretor mass, M 1 (M ) 0.87(2) Donor mass, M 2 (M ) 0.0250(13) Accretor radius, R 1 (R ) 0.0092(3) Donor radius, R 2 (R ) 0.060(10) Disc radius, R disc (R ) 0.264(3) Bright spot separation, R spot (R ) 0.187 (2) Accretor orbital velocity, K WD (km/s) 17.6 ± 1.0

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