The SOFIA Massive (SOMA) Star Formation Survey. I. Overview and First
  Results
  We present an overview and first results of the Stratospheric Observatory For
Infrared Astronomy Massive (SOMA) Star Formation Survey, which is using the
FORCAST instrument to image massive protostars from
$\sim10$--$40\:\rm{\mu}\rm{m}$. These wavelengths trace thermal emission from
warm dust, which in Core Accretion models mainly emerges from the inner regions
of protostellar outflow cavities. Dust in dense core envelopes also imprints
characteristic extinction patterns at these wavelengths, causing intensity
peaks to shift along the outflow axis and profiles to become more symmetric at
longer wavelengths. We present observational results for the first eight
protostars in the survey, i.e., multiwavelength images, including some
ancillary ground-based MIR observations and archival {\it{Spitzer}} and
{\it{Herschel}} data. These images generally show extended MIR/FIR emission
along directions consistent with those of known outflows and with shorter
wavelength peak flux positions displaced from the protostar along the
blueshifted, near-facing sides, thus confirming qualitative predictions of Core
Accretion models. We then compile spectral energy distributions and use these
to derive protostellar properties by fitting theoretical radiative transfer
models. Zhang and Tan models, based on the Turbulent Core Model of McKee and
Tan, imply the sources have protostellar masses $m_*\sim10$--50$\:M_\odot$
accreting at $\sim10^{-4}$--$10^{-3}\:M_\odot\:{\rm{yr}}^{-1}$ inside cores of
initial masses $M_c\sim30$--500$\:M_\odot$ embedded in clumps with mass surface
densities $\Sigma_{\rm{cl}}\sim0.1$--3$\:{\rm{g\:cm}^{-2}}$. Fitting Robitaille
et al. models typically leads to slightly higher protostellar masses, but with
disk accretion rates $\sim100\times$ smaller. We discuss reasons for these
differences and overall implications of these first survey results for massive
star formation theories.
