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Keck Measurement of the XTE J2123-058 Radial Velocity Curve

John A. Tomsick·William A. Heindl·Deepto Chakrabarty·Jules P. Halpern·Philip Kaaret
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Abstract

We measured the radial velocity curve of the companion of the neutron star X-ray transient XTE J2123-058. Its semi-amplitude (K_2) of 298.5 +/- 6.9 km/s is the highest value that has been measured for any neutron star LMXB. The high value for K_2 is, in part, due to the high binary inclination of the system but may also indicate a high neutron star mass. The mass function (f_2) of 0.684 +/- 0.047 solar masses, along with our constraints on the companion's spectral type (K5V-K9V) and previous constraints on the inclination, gives a likely range of neutron star masses from 1.2 to 1.8 solar masses. We also derive a source distance of 8.5 +/- 2.5 kpc, indicating that XTE J2123-058 is unusually far, 5.0 +/- 1.5 kpc, from the Galactic plane. Our measurement of the systemic radial velocity is -94.5 +/- 5.5 km/s, which is significantly different from what would be observed if this object corotates with the disk of the Galaxy.

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John A. Tomsick, William A. Heindl, Deepto Chakrabarty, Jules P. Halpern, Philip Kaaret. 2001-08-15. Keck Measurement of the XTE J2123-058 Radial Velocity Curve. https://doi.org/10.1086/323752

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