IPA: Class 0 Protostars Viewed in CO Emission Using JWST

We investigate the bright CO fundamental emission in the central regions of five protostars in their primary mass assembly phase using new observations from JWST's Near-Infrared Spectrograph and Mid-Infrared Instrument. CO line emission images and fluxes are extracted for a forest of similar to 150 rovibrational transitions from two vibrational bands, v = 1-0 and v = 2-1. However, 13CO is undetected, indicating that 12CO emission is optically thin. We use H2 emission lines to correct fluxes for extinction and then construct rotation diagrams for the CO lines with the highest spectral resolution and sensitivity to estimate rotational temperatures and numbers of CO molecules. Two distinct rotational temperature components are required for v = 1 (similar to 600 to 1000 K and 2000 to similar to 104 K), while one hotter component is required for v = 2 (greater than or similar to 3500 K). 13CO is depleted compared to the abundances found in the interstellar medium, indicating selective UV photodissociation of 13CO; therefore, UV radiative pumping may explain the higher rotational temperatures in v = 2. The average vibrational temperature is similar to 1000 K for our sources and is similar to the lowest rotational temperature components. Using the measured rotational and vibrational temperatures to infer a total number of CO molecules, we find that the total gas masses range from lower limits of similar to 1022 g for the lowest mass protostars to similar to 1026 g for the highest mass protostars. Our gas mass lower limits are compatible with those in more evolved systems, which suggest the lowest rotational temperature component comes from the inner disk, scattered into our line of sight, but we also cannot exclude the contribution to the CO emission from disk winds for higher mass targets.