2007A&A...473..523V -
Astronomy and Astrophysics, volume 473, 523-538 (2007/10-2)
Determination of the mass of the neutron star in SMC X-1, LMC X-4, and Cen X-3 with VLT/UVES.
VAN DER MEER A., KAPER L., VAN KERKWIJK M.H., HEEMSKERK M.H.M. and VAN DEN HEUVEL E.P.J.
Abstract (from CDS):
We present the results of a spectroscopic monitoring campaign of the OB-star companions to the eclipsing X-ray pulsars
SMC X-1,
LMC X-4 and
Cen X-3. High-resolution optical spectra obtained with UVES on the ESO Very Large Telescope are used to determine the radial-velocity orbit of the OB (super)giants with high precision. The excellent quality of the spectra provides the opportunity to measure the radial-velocity curve based on individual lines, and to study the effect of possible distortions of the line profiles due to e.g. X-ray heating on the derived radial-velocity amplitude. Several spectral lines show intrinsic variations with orbital phase. The magnitude of these variations depends on line strength, and thus provides a criterion to select lines that do not suffer from distortions. The undistorted lines show a larger radial-velocity amplitude than the distorted lines, consistent with model predictions. Application of our line-selection criteria results in a mean radial-velocity amplitude K
opt of 20.2±1.1, 35.1±1.5, and 27.5±2.3km/s (1σ errors), for the OB companion to
SMC X-1,
LMC X-4 and
Cen X-3, respectively. Adding information on the projected rotational velocity of the OB companion (derived from our spectra), the duration of X-ray eclipse and orbital parameters of the X-ray pulsar (obtained from literature), we arrive at a neutron star mass of 1.06
+0.11–0.10, 1.25
+0.11–0.10 and 1.34
+0.16–0.14M
☉ for
SMC X-1,
LMC X-4 and
Cen X-3, respectively. The mass of
SMC X-1 is near the minimum mass (∼1M
☉) expected for a neutron star produced in a supernova. We discuss the implications of the measured mass distribution on the neutron-star formation mechanism, in relation to the evolutionary history of the massive binaries.
Abstract Copyright:
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Journal keyword(s):
stars: binaries: eclipsing - stars: neutron - stars: general - equation of state - accretion, accretion disks
VizieR on-line data:
<Available at CDS (J/A+A/473/523): smcx1/* lmcx4/* cenx3/*>
Simbad objects:
33
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