1999ApJ...526..845M

An ideal molecular probe for tracing the kinetic temperature in dense molecular cloud cores should allow the temperature determination to be independent of gas density effects. The formaldehyde (H₂CO) molecule, a slightly asymmetrical rotor, is just such a molecule. By using several sets of judiciously chosen H₂CO line ratios, we have reliably determined the gas kinetic temperatures of the dense gas condensations within the NGC 2024 star formation region. Our measurements indicate T_K>40 K toward the embedded sources FIR3-FIR7. These sources, which had previously been identified as isothermal protostars, are likely in a more evolved state.