The Runaways and Isolated O-Type Star Spectroscopic Survey of the SMC
  (RIOTS4)
  We present the Runaways and Isolated O-Type Star Spectroscopic Survey of the
SMC (RIOTS4), a spatially complete survey of uniformly selected field OB stars
that covers the entire star-forming body of the SMC. Using the IMACS multislit
spectrograph and MIKE echelle spectrograph on the Magellan telescopes, we
obtained spectra of 374 early-type field stars that are at least 28 pc from any
other OB candidates. We also obtained spectra of an additional 23 field stars
in the SMC bar identified from slightly different photometric criteria. Here,
we present the observational catalog of stars in the RIOTS4 survey, including
spectral classifications and radial velocities. For three multi-slit fields
covering 8% of our sample, we carried out monitoring observations over 9-16
epochs to study binarity, finding a spectroscopic, massive binary frequency of
at least $\sim$60% in this subsample. Classical Oe/Be stars represent a large
fraction of RIOTS4 (42%), occurring at much higher frequency than in the
Galaxy, consistent with expectation at low metallicity. RIOTS4 confirmed a
steep upper IMF in the field, apparently caused by the inability of the most
massive stars to form in the smallest clusters. Our survey also yields evidence
for in-situ field OB star formation, and properties of field emission-line star
populations, including sgB[e] stars and classical Oe/Be stars. We also discuss
the radial velocity distribution and its relation to SMC kinematics and runaway
stars. RIOTS4 presents a first quantitative characterization of field OB stars
in an external galaxy, including the contributions of sparse, but normal, star
formation; runaway stars; and candidate isolated star formation.
