The SOFIA Massive (SOMA) Star Formation Survey

Massive stars are important throughout astrophysics, but their formation mechanism remains the subject of much debate. SOFIA is uniquely capable of probing the highly extincted regions in which massive star formation is taking place. Following our study of G35.20-0.74 with SOFIA-FORCAST in Basic Science (Zhang et al. 2013), we started the SOMA Survey with the goal of eventually observing about 50 high- and intermediate-mass protostars across a range of Galactic environments and evolutionary stages. So far, just over 20 sources have been observed. FORCAST provides high dynamic range images from ~8 to 40 microns, allowing characterization of massive protostars, including their fainter extented emission, which is often shaped by the presence of outflow cavities. FORCAST data are crucial for constraining the spectral energy distribution (SED) of these protostars at the wavelengths where the bulk of the bolometric flux is emerging. Also, this thermal emission from warm dust is much easier to model than that at shorter wavelengths (<10 microns), which is affected by PAH emission features. Detailed radiative transfer models of massive protostars based on the Turbulent Core Model (McKee & Tan 2002, 2003) have been developed by Zhang et al. (2014). In the first SOMA Survey paper (De Buizer et al. 2017), we have tested these models on the SEDs of eight protostars and compared our results to those obtained from the widely used Robitaille et al. (2007) models, finding significant differences. Protostellar parameters derived from SED fitting alone suffer from significant degeneracies. I discuss how these may be broken by considering multiwavelength imaging data, and other ancillary data. Finally, I summarize follow-up observations of the SOMA Survey sources, including with ALMA and HST, and future prospects.