The spectral distributions of Be/X-ray binaries in the Large Magellanic Cloud and Galaxy have been shown to differ significantly from the distributio

We have monitored 41 Be/X-ray binary systems in the Small Magellanic Cloud over ~9 years using PCA-RXTE data from a weekly survey program. The resulting light curves were analysed in search of orbital modulations with the result that 10 known orbital ephemerides were confirmed and refined, while 10 new ones where determined. A large number of X-ray orbital profiles are presented for the first time, showing similar characteristics over a wide range of orbital periods. Lastly, three pulsars: SXP46.4, SXP89.0 and SXP165 were found to be misidentifications of SXP46.6, SXP91.1 and SXP169, respectively.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

We present high-speed photometric observations of 20 faint cataclysmic variables (CVs) selected from the Sloan Digital Sky Survey (SDSS) and Catalina catalogues. Measurements are given of 15 new directly measured orbital periods, including four eclipsing dwarf novae (SDSS 0904+03, CSS 0826−00, CSS 1404−10 and CSS 1626−12), two new polars (CSS 0810+00 and CSS 1503−22) and two dwarf novae with superhumps in quiescence (CSS 0322+02 and CSS 0826−00). Whilst most of the dwarf novae presented here have periods below 2 h, SDSS 0805+07 and SSS 0617−36 have relatively long orbital periods of 5.489 and 3.440 h, respectively. The double-humped orbital modulations observed in SSS 0221−26, CSS 0345−01, CSS 1300+11 and CSS 1443−17 are typical of low-mass transfer rate dwarf novae. The white dwarf primary of SDSS 0919+08 is confirmed to have non-radial oscillations, and quasi-periodic oscillations were observed in the short-period dwarf nova CSS 1028−08 during outburst. We further report the detection of a new nova-like variable (SDSS 1519+06). The frequency distribution of orbital periods of CVs in the Catalina Real-time Transient Survey (CRTS) has a high peak near ∼80 min orbital period, independently confirming that found by Gänsicke et al. from SDSS sources. We also observe a marked correlation between the median in the orbital period distribution and the outburst class, in the sense that dwarf novae with a single observed outburst (over the 5-year baseline of the CRTS coverage) occur predominantly at shortest orbital period.

We combine the decade-long photometry of the Be/X-ray binary system A0538–66 provided by the Massive astrophysical compact halo object (MACHO) and optical gravitational lensing experiment (OGLE) IV projects with high-resolution Southern African Large Telescope (SALT) spectroscopy to provide detailed constraints on the orbital parameters and system properties. The ∼420 d superorbital modulation is present throughout, but has reduced in amplitude in recent years. The well-defined 16.6409 d orbital outbursts, which were a strong function of superorbital phase in the MACHO data (not occurring at all at superorbital maximum), are present throughout the OGLE IV coverage. However, their amplitude reduces during superorbital maximum. We have refined the orbital period and ephemeris of the optical outburst based on ∼25 yr light curves to HJD = 2455674.48 ± 0.03 + n*16.6409 ± 0.0003d. Our SALT spectra reveal a B1 III star with vsin i of 285 kms⁻¹ from which we have derived an orbital radial velocity curve which confirms the high eccentricity of e = 0.72 ± 0.14. Furthermore, the mass function indicates that, unless the neutron star far exceeds the canonical 1.44 M_⊙, the donor must be significantly undermassive for its spectral type. We discuss the implications of the geometry and our derived orbital solution on the observed behaviour of the system.