Astrochemical Diagnostics of the Isolated Massive Protostar G28.20-0.05

We study the astrochemical diagnostics of the isolated massive protostar G28.20-0.05. We analyze data from Atacama Large Millimeter/submillimeter Array 1.3 mm observations with a resolution of 0.'' 2 (similar to 1000 au). We detect emission from a wealth of species, including oxygen-bearing (e.g., H2CO, CH3OH, CH3OCH3), sulfur-bearing (SO2, H2S), and nitrogen-bearing (e.g., HNCO, NH2CHO, C2H3CN, C2H5CN) molecules. We discuss their spatial distributions, physical conditions, correlation between different species, and possible chemical origins. In the central region near the protostar, we identify three hot molecular cores (HMCs). HMC1 is part of a millimeter continuum ring-like structure, is closest in projection to the protostar, has the highest temperature of similar to 300 K, and shows the most line-rich spectra. HMC2 is on the other side of the ring, has a temperature of similar to 250 K, and is of intermediate chemical complexity. HMC3 is further away, similar to 3000 au in projection, cooler (similar to 70 K), and is the least line-rich. The three HMCs have similar mass surface densities (similar to 10 g cm-2), number densities (n H similar to 109 cm-3), and masses of a few solar masses. The total gas mass in the cores and in the region out to 3000 au is similar to 25 M circle dot, which is comparable to that of the central protostar. Based on spatial distributions of peak line intensities as a function of excitation energy, we infer that the HMCs are externally heated by the protostar. We estimate column densities and abundances of the detected species and discuss the implications for hot core astrochemistry.