Bibcode
Cornelisse, R.; Steeghs, D.; Casares, J.; Charles, P. A.; Shih, I. C.; Hynes, R. I.; O'Brien, K.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 381, Issue 1, pp. 194-200.
Advertised on:
10
2007
Citations
11
Refereed citations
7
Description
Two nights of phase-resolved medium-resolution Very Large Telescope
spectroscopy of the extra-galactic low-mass X-ray binary LMCX-2 have
revealed a 0.32 +/- 0.02 d spectroscopic period in the radial velocity
curve of the HeII λ4686 emission line that we interpret as the
orbital period. However, similar to previous findings, this radial
velocity curve shows a longer term variation that is most likely due to
the presence of a precessing accretion disc in LMCX-2. This is
strengthened by HeII λ4686 Doppler maps that show a bright spot
that is moving from night to night. Furthermore, we detect narrow
emission lines in the Bowen region of LMCX-2, with a velocity of
Kem = 351 +/- 28 km s-1, that we tentatively
interpret as coming from the irradiated side of the donor star. Since
Kem must be smaller than K2, this leads to the
first upper limit on the mass function of LMCX-2 of f(M1)
>= 0.86 Msolar (95 per cent confidence), and the first
constraints on its system parameters.