Showing papers by "M. H. van Kerkwijk published in 1996"

The Masses of the Millisecond Pulsar J1012+5307 and Its White Dwarf Companion

Abstract: We report on spectroscopy of the white dwarf companion of the millisecond radio pulsar PSR J1012+5307. We find strong Balmer absorption lines, as would be expected for a cool DA white dwarf. The profiles are much narrower than usual, however, and lines are seen up to H12, indicating that the companion has a low gravity and hence a low mass. This is consistent with the expectation—based on evolutionary considerations and on the mass function—that it is a low-mass white dwarf with a helium core. By comparing the spectra to model atmospheres, we derive an effective temperature Teff = 8550 ± 25 K and a surface gravity log g = 6.75 ± 0.07 cgs. Using the Hamada-Salpeter mass-radius relation for helium white dwarfs, with an approximate correction for finite-temperature effects, we infer a mass MWD = 0.16 ± 0.02 M☉. This is the lowest mass among all spectroscopically identified white dwarfs. We determine radial velocities from our spectra, and we find a radial-velocity amplitude of 280 ± 15 km s-1. With the pulsar's radial-velocity amplitude, the mass ratio MPSR/MWD = 13.3 ± 0.7. From all constraints, we find that with 95% confidence, 1.5 < MPSR/M☉ < 3.2.

A Survey for Millisecond Pulsars

Abstract: We have searched 960 square degrees of sky for radio pulsars, using the 305 m telescope at Arecibo, Puerto Rico. The 430 MHz survey reached a limiting sensitivity for slow pulsars of 0.7 mJy using a dual-polarization, 32 channel filter bank over 8 MHz of bandwidth. We have detected one new millisecond pulsar, 11 new slow pulsars, one previously known millisecond pulsar, and eight previously known slow pulsars. The new millisecond pulsar, PSR J2033 +17, with a period of 5.9 ms, has been found to be in a binary system. The Keplerian circular orbital solution has a period of 56.2 days and a semimajor axis of 20.7 lt-s. One of the slow pulsars, PSR J2043+2740, is the second fastest pulsar that is not either recycled or associated with a supernova remnant. It is near the Cygnus Loop remnant, but timing measurements imply a pulsar characteristic age of 1.2 Myr, which makes an association unlikely.

The Wolf-Rayet counterpart of Cygnus X-3

Abstract: We present orbital-phase resolved I and K-band spectroscopy of Cygnus X-3. All spectra show emission lines characteristic of Wolf-Rayet stars of the WN subclass. On time scales longer than about one day, the line strengths show large changes, both in flux and in equivalent width. In addition, the line ratios change, corresponding to a variation in spectral subtype of WN6/7 to WN4/5. We confirm the finding that at times when the emission lines are weak, they shift in wavelength as a function of orbital phase, with maximum blueshift coinciding with infrared and X-ray minimum, and maximum redshift half an orbit later. Furthermore, we confirm the prediction -- made on the basis of previous observations -- that at times when the emission lines are strong, no clear wavelength shifts are observed. We describe a simplified, but detailed model for the system, in which the companion of the X-ray source is a Wolf-Rayet star whose wind is at times ionised by the X-ray source, except for the part in the star's shadow. With this model, the observed spectral variations can be reproduced with only a small number of free parameters. We discuss and verify the ramifications of this model, and find that, in general, the observed properties can be understood. We conclude that Cyg X-3 is a Wolf-Rayet/X-ray binary.

The Wolf-Rayet counterpart of Cygnus X-3

Abstract: We present orbital-phase resolved I and K-band spectroscopy of Cygnus X-3. All spectra show emission lines characteristic of Wolf-Rayet stars of the WN subclass. On time scales longer than about one day, the line strengths show large changes, both in flux and in equivalent width. In addition, the line ratios change, corresponding to a variation in spectral subtype of WN6/7 to WN4/5. We confirm the finding that at times when the emission lines are weak, they shift in wavelength as a function of orbital phase, with maximum blueshift coinciding with infrared and X-ray minimum, and maximum redshift half an orbit later. Furthermore, we confirm the prediction -- made on the basis of previous observations -- that at times when the emission lines are strong, no clear wavelength shifts are observed. We describe a simplified, but detailed model for the system, in which the companion of the X-ray source is a Wolf-Rayet star whose wind is at times ionised by the X-ray source, except for the part in the star's shadow. With this model, the observed spectral variations can be reproduced with only a small number of free parameters. We discuss and verify the ramifications of this model, and find that, in general, the observed properties can be understood. We conclude that Cyg X-3 is a Wolf-Rayet/X-ray binary.

The White Dwarf Companions of Recycled Pulsars

Abstract: I review what properties of the white-dwarf companions of recycled pulsars can be inferred from optical observations, and discuss how these can help us understand the characteristics and evolution of these binaries. I focus on spectroscopic observations, describing results obtained recently, and looking forward to what may come.

The White Dwarf Companions of Recycled Pulsars

Abstract: I review what properties of the white-dwarf companions of recycled pulsars can be inferred from optical observations, and discuss how these can help us understand the characteristics and evolution of these binaries. I focus on spectroscopic observations, describing results obtained recently, and looking forward to what may come.