Temperature profiles of young disk-like structures The case of IRAS 16293A star

Journal article, 2020

Context. Temperature is a crucial parameter in circumstellar disk evolution and planet formation because it governs the resistance of the gas to gravitational instability and sets the chemical composition of the planet-forming material. Aims. We set out to determine the gas temperature of the young disk-like structure around the Class 0 protostar IRAS 16293-2422A. Methods. We used Atacama Large Millimeter/submillimeter Array (ALMA) observations of multiple H2CS J = 7 - 6 and J = 10 - 9 lines from the Protostellar Interferometric Line Survey (PILS) to create a temperature map for the inner similar to 200 AU of the disk-like structure. This molecule is a particularly useful temperature probe because transitions between energy levels with different K-a quantum numbers operate only through collisions. Results. Based on the H2CS line ratios, the temperature is between similar to 100-175 K in the inner similar to 150 AU, and drops to similar to 75 K at similar to 200 AU. At the current resolution (0.5 ''similar to 70 AU), no jump is seen in the temperature at the disk-envelope interface. Conclusions. The temperature structure derived from H2CS is consistent with envelope temperature profiles that constrain the temperature from 1000 AU scales down to similar to 100 AU, but does not follow the temperature rise seen in these profiles at smaller radii. Higher angular resolution observations of optically thin temperature tracers are needed to establish whether cooling by gas-phase water, the presence of a putative disk, or the dust optical depth influences the gas temperature at less than or similar to 100 AU scales. The temperature at 100 AU is higher in IRAS 16293A than in the embedded Class 0/I disk L1527, consistent with the higher luminosity of the former.