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Abstract. We report new radial velocity observations of GP Vel / HD 77581, the optical companion to the eclipsing X-ray pulsar Vela X-1. Using data spanning more than two complete orbits of the system, we detect evidence for tidally induced nonradial oscillations on the surface of GP Vel, apparent as peaks in the power spectrum of the residuals to the radial velocity curve fit. By removing the effect of these oscillations (to first order) and binning the radial velocities, we have determined the semiamplitude of the radial velocity curve of GP Vel to be K o = 22.6 ± 1.5 km s −1 . Given the accurately measured semi-amplitude of the pulsar's orbit, the mass ratio of the system is 0.081 ± 0.005. We are able to set upper and lower limits on the masses of the component stars as follows. Assuming GP Vel fills its Roche lobe then the inclination angle of the system, i, is 70.1• ± 2.6• . In this case we obtain the masses of the two stars as M x = 2.27 ± 0.17 M for the neutron star and M o = 27.9 ± 1.3 M for GP Vel. Conversely, assuming the inclination angle is i = 90• , the ratio of the radius of GP Vel to the radius of its Roche lobe is β = 0.89 ± 0.03 and the masses of the two stars are M x = 1.88 ± 0.13 M and M o = 23.1 ± 0.2 M . A range of solutions between these two sets of limits is also possible, corresponding to other combinations of i and β. In addition, we note that if the zero phase of the radial velocity curve is allowed as a free parameter, rather than constrained by the X-ray ephemeris, a significantly improved fit is obtained with an amplitude of 21.2 ± 0.7 km s −1 and a phase shift of 0.033 ± 0.007 in true anomaly. The apparent shift in the zero phase of the radial velocity curve may indicate the presence of an additional radial velocity component at the orbital period. This may be another manifestation of the tidally induced non-radial oscillations and provides an additional source of uncertainty in the determination of the orbital radial velocity amplitude.

Contents 9 Jets from X-ray binaries page 1 9.1 History 2 9.2 Physical properties of the jets 3 9.3 Ubiquity 14 9.4 Disc-jet coupling in black hole binaries 15 9.5 Disc-jet coupling in neutron star binaries 26 9.6 High energy / particle emission from jets 29 9.7 Interactions 32 9.8 Relation to other jet sources 34 9.9 On the origin of jets 36 9.10 Conclusions 39 Bibliography 40 HistoryRelativistic outflows, or 'Jets', represent one of the most obvious, important and yet poorly-explained phenomena associated with accreting relativistic objects, including X-ray binaries. Originally recognised in images as long, thin structures apparently connected at one end to the nuclei of galaxies, it was soon established that they represent powerful flows of energy and matter away from accreting black holes and back to the Universe at large. From their earliest association with the most luminous sources in the Universe, the Active Galactic Nuclei (AGN), the conclusion could have been drawn that jets were a common consequence of the process of accretion onto relativistic objects. Nevertheless, their association with the analogous accretion processes involving stellar-mass black holes and neutron stars was not systematically explored until the past decade or so.Although it is now clear that the electromagnetic radiation from X-ray binary jets may extend to at least the X-ray band, historically the key observational aspect of jets is their radio emission. High brightness temperatures (see section 9.2), 'nonthermal' spectra and polarisation measurements indicate an origin as synchrotron emission from relativistic electrons. Following the discovery of luminous binary X-ray sources in the 1960s and 1970s, radio counterparts were associated with the brightest of these, e.g. Sco X-1 (Hjellming & Wade 1971a), Cyg X-1 (Hjellming & Wade 1971b) and the outbursting source Cyg X-3 (Gregory et al. 1972 et seq.

We report imaging photometry of the radio-jet black hole candidate source GRS 1915+105 in the infrared K band. The observations reveal rapid infrared flare events on timescales of less than an hour. These events are strikingly similar to those regularly observed in radio monitoring at 15 GHz. Furthermore, when dereddened, the infrared events have comparable amplitudes to the radio oscillations, and observations at 15 GHz made ∼ 8 hr after our infrared observations reveal that the source was indeed displaying radio oscillations at this time. We suggest that we have observed infrared synchrotron emission from this source. We estimate the equipartition magnetic field and power required to accelerate the particles for the repeated radio events, and find both to be orders of magnitude greater than those estimated for any other X-ray binary.Comparison of events at 15 GHz and 2.2 µm suggests that the dominant loss mechanism is adiabatic expansion, which in turn implies that each event corresponds to a small ejection of material from the system.

The CORNISH project is the highest resolution radio continuum survey of the Galactic plane to date. It is the 5 GHz radio continuum part of a series of multi-wavelength surveys that focus on the northern GLIMPSE region (10 • < l < 65 • ), observed by the Spitzer satellite in the mid-infrared. Observations with the Karl G. Jansky Very Large Array (VLA) in B and BnA configurations have yielded a 1.5 ′′ resolution Stokes I map with a root-mean-squared noise level better than 0.4 mJy beam −1 . Here we describe the data-processing methods and data characteristics, and present a new, uniform catalogue of compact radioemission. This includes an implementation of automatic deconvolution that provides much more reliable imaging than standard CLEANing. A rigorous investigation of the noise characteristics and reliability of source detection has been carried out. We show that the survey is optimised to detect emission on size scales up to 14 ′′ and for unresolved sources the catalogue is more than 90 percent complete at a flux density of 3.9 mJy. We have detected 3,062 sources above a 7σ detection limit and present their ensemble properties. The catalogue is highly reliable away from regions containing poorly-sampled extended emission, which comprise less than two percent of the survey area. Imaging problems have been mitigated by downweighting the shortest spacings and potential artefacts flagged via a rigorous manual inspection with reference to the Spitzer infrared data. We present images of the most common source types found: H II regions, planetary nebulae and radio-galaxies. The CORNISH data and catalogue are available online at http://cornish.leeds.ac.uk.Note.-The properties of the data differ in the combination of antenna types included in the array, the configuration of the array, the weather experienced and the declination range observed. Unless otherwise noted the weather during the observations was reasonable.