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.
The UV emission lines of Hercules X-1, resolved with the HST GHRS and STIS, can be divided into broad (FWHM≈ 750 km s −1 ) and narrow (FWHM≈ 150 km s −1 ) components. The broad lines can be unambiguously identified with emission from an accretion disk which rotates prograde with the orbit. The narrow lines, previously identified with the X-ray illuminated atmosphere of the companion star, are blueshifted at both φ = 0.2 and φ = 0.8 and the line flux at φ = 0.2 is ≈ 0.2 of the flux at φ = 0.8. Line ratio diagnostics show that the density of the narrow line region is log n e = 13.4 ± 0.2 and T e = 1.0 ± 0.2 × 10 5 K. The symmetry of the eclipse ingress suggests that the line emission on the surface of the disk is left-right symmetric relative to the orbit. Model fits to the O V, Si IV, and He II line profiles agree with this result, but fits to the N V lines suggest that the receding side of the disk is brighter. We note that there are narrow absorption components in the N V lines with blueshifts of ≈ 500 km s −1 .
Abstract. We present optical photometry, spectroscopy and photopolarimetry, as well as ASCA X-ray observations, of the recently discovered intermediate polar 1WGA J1958.2+3232. Through the first detection of an optical beat frequency, we confirm the previously tentative suggestion that the spin period of the white dwarf is twice the X-ray and optical pulsation period, which we also confirm in each case. We detect an orbital modulation in each of the U , B, V , R and I bands for the first time, and suggest that the true orbital period is the −1d alias of that previously suggested. We also confirm the presence of circular polarization in this system, detecting a variable polarization which has opposite signs in each of the B and R bands. The double peaked pulse profile and oppositely signed polarization pulses suggest that 1WGA J1958.2+3232 accretes onto both magnetic poles via a disc which is truncated relatively close to the white dwarf.
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