NGC 7538 IRS 1 is one of the many IR-bright, young stellar objects (YSO) within the HII region NGC 7538, in the Perseus’ arm of the Milky Way. IRS 1 is still actively accreting mass, offering one of the best perspectives into the very first stages of star formation. The composition of the protostar’s envelope can be used to retrace the early processing of gas, dust and PAHs by the UV radiation field, which should be strongly absorbed during this young phase. SOFIA extensively observed IRS 1 in the mid and far-IR, providing:

  • photometric images at 7.7, 19.7, 25.3, 31.5 and 37.1 µm, which can be used to distinguish the infrared contributions from dust and PAHs, the latter being mainly constrained by the emission level at 7.7 µm (FORCAST, project 01_0034)
  • spectrally-resolved images (R~600 and R~1000) covering 75-95 µm and 135-155 µm. The derived far-IR  photometry can refine the source’s SED and constrain the temperature, emissivity and size distribution of the colder dust component, as shown by Sandell et al., 2020 with mid-IR data. Gas-phase transitions for atomic, ionized and molecular species may also be detectable (FIFI-LS, project 03_0151)
  • high-resolution spectra from 5.5 to 27 µm, covering ro-vibrational transitions of several gas-phase components - H2O, HCN, C2H2, CS, SO2, CH4, CH3, NH3. the availability of low and high-J transitions (across P, Q- R-branches) for CH4, HCN, H2O and SO2 can allow one to derive the abundance of these molecules in a comprehensive way, tracing both cold and warm gas components (EXES, projects 02_0104, 03_0080, 04_0120, 75_0024). Indriolo et al. 20152020, demonstrate the analysis of similar EXES H2O data in protostars. 

All calibrated data are available from the IRSA SOFIA Archive.

Three-color image of the IRS 1 – 3 region

Three-color image of the IRS 1 – 3 region generated by combining the FORCAST 19 (blue), 25 (green), and 37 µm (red) images in logarithmic scale. IRS 1 is the strong yellow source at offset 0′′, 0′′. IRS 2 at 0′′ . 7, +9′′ . 6, is the extended blueish source with a size of ∼ 10′′. The third strong source, IRS 3 is at -13′′ , +2′′ . 6. IRS 4 is at the northwestern part of the image and not fully covered in this image. IRS 1 E is the faint source east of IRS 1 and IRS 1 SE is not really visible in this color image.

Sandell et al. 2020
HII region
star formation
multiwavelength study
interstellar and intergalactic medium
massive stars
Emission lines
stellar evolution and models
Young stars and protostellar objects