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Arxiv: IPA: Class 0 Protostars Viewed in CO Emission Using JWST Published: 12/13/2023 2:04:19 AM Updated: 9/10/2024 8:13:49 PM

Paper abstract: We investigate the bright CO fundamental emission in the central regions offive protostars in their primary mass assembly phase using new observationsfrom JWST's Near-Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument(MIRI). CO line emission images and fluxes are extracted for a forest of~150 ro-vibrational transitions from two vibrational bands, v=1-0 andv=2-1. However, {}^{13}CO is undetected, indicating that {}^{12}COemission is optically thin. We use H_2 emission lines to correct fluxes forextinction and then construct rotation diagrams for the CO lines with thehighest spectral resolution and sensitivity to estimate rotational temperaturesand numbers of CO molecules. Two distinct rotational temperature components arerequired for v=1 (~600 to 1000 K and 2000 to ~ 10^4 K), while onehotter component is required for v=2 (\gtrsim 3500 K). {}^{13}CO isdepleted compared to the abundances found in the ISM, indicating selective UVphotodissociation of {}^{13}CO; therefore, UV radiative pumping may explainthe higher rotational temperatures in v=2. The average vibrationaltemperature is ~ 1000 K for our sources and is similar to the lowestrotational temperature components. Using the measured rotational andvibrational temperatures to infer a total number of CO molecules, we find thatthe total gas masses range from lower limits of ~10^{22} g for the lowestmass protostars to ~ 10^{26} g for the highest mass protostars. Our gasmass lower limits are compatible with those in more evolved systems, whichsuggest the lowest rotational temperature component comes from the inner disk,scattered into our line of sight, but we also cannot exclude the contributionto the CO emission from disk winds for higher mass targets.