We report high-resolution optical spectroscopy of the low-mass X-ray binary V395 Car/2S 0921–630 obtained with the MIKE echelle spectrograph on the Magellan-Clay telescope .
Our spectra are obtained near inferior conjunction of the mass donor star and we exploit the absorption lines originating from the back-side of the K-type object to accurately derive its rotational velocity .
Using K0-K1 III templates , we find v \sin { i } = 32.9 \pm 0.8 km s ^ { -1 } .
We show that the choice of template star and the assumed limb darkening coefficient has little impact on the derived rotational velocity .
This value is a significant revision downwards compared to previously published values .
We derive new system parameter constraints in the light of our much lower rotational velocity .
We find M _ { 1 } = 1.44 \pm 0.10 M _ { \odot } , M _ { 2 } = 0.35 \pm 0.03 M _ { \odot } , and q = 0.24 \pm 0.02 where the errors have been estimated through a Monte-Carlo simulation .
A possible remaining systematic effect is the fact that we may be over-estimating the orbital velocity of the mass donor due to irradiation effects .
However , any correction for this effect will only reduce the compact object mass further , down to a minimum mass of M _ { 1 } = 1.05 \pm 0.08 M _ { \odot } .
There is thus strong evidence that the compact object in this binary is a neutron star of rather typical mass and that the previously reported mass values of 2-4 M _ { \odot } were too high due to an over-estimate of the rotational broadening .