HD 314884: A slowly pulsating B star in a close binary

We present the results of a spectroscopic and photometric analysis of HD 314884, a slowly pulsating B star (SPB) in a binary system with detected soft-X-ray emission. We spectrally classify the B star as a B5V-B6V star with T_eff = 15 490 ± 310 K, log g = 3.75 ± 0.25 dex, and a photometric period of P0 = 0.889 521(12) d. A spectroscopic period search reveals an orbital period for the system of P_orb = 1.3654(11) d. The discrepancy in the two periods and the identification of a second and third distinct frequency in the photometric Fourier transform at P₁ = 3.1347(56) and P₂ = 1.517(28) d provides evidence that HD 314884 is an SPB with at least three oscillation frequencies. These frequencies appear to originate from higher order, non-linear tidal pulsations. Using the dynamical parameters obtained from the radialvelocity curve, we find the most probable companion mass to be M₁ =~0.8 M_⊙ assuming a typical mass for the B star and most probable inclination. We conclude that the X-ray source companion to HD 314884 is most likely a coronally active G-type star or a white dwarf, with no apparent emission lines in the optical spectrum. The mass probability distribution of the companion star mass spans 0.6-2.3M_⊙ at 99 per cent confidence which allows the possibility of a neutron star companion. The X-ray source is unlikely to be a black hole unless it is of a very low mass or low binary inclination.