New Field OB and OBe Binaries of the SMC Wing: Observational Properties and Population Modeling

Abstract We present a radial velocity (RV) survey of the field OB and OBe stars of the SMC Wing. We use multiepoch observations of 55 targets obtained with the Magellan Inamori-Magellan Aerial Camera and Spectrograph and M2FS multi-object spectrographs to identify single- and double-lined spectroscopic binaries. We also use TESS light curves to identify new eclipsing binary candidates. We find that 10 each of our 34 OB (29%) and 21 OBe (48%) stars are confirmed binaries, and at least ∼6 more are candidates. Using our RV measurements, we set constraints on the companion masses, and in some cases, on periods, eccentricities, and inclinations. The RV data suggest that OB binaries favor more circular orbits (mean eccentricity 〈 e 〉 = 0.08 ± 0.02), while OBe binaries are eccentric (〈 e 〉 = 0.45 ± 0.04). We identify two candidate black hole binaries, [M2002] 77616, and 81941. We use Binary Population and Spectral Synthesis to predict the frequencies of ejected OB and OBe stars and binaries, assuming OBe stars are binary mass gainers ejected by the companion supernova. We also predict the frequencies of black-hole, neutron-star, and stripped-star companions, and we model the distributions of primary and secondary masses, periods, eccentricities, and velocity distributions. The models are broadly consistent with the binary origin scenario for OBe stars, and predict an even larger number of post-supernova OB binaries. Comparison with the kinematics supports a significant contribution from dynamical ejections for both OB and OBe stars, although less so for binaries.