Observation of the C I ³P₂-³P₁ line toward the Orion Kleinmann-Low region

The ³P₂-³P₁ fine-structure line of the neutral carbon atom (809 GHz) has been observed toward the Orion Kleinmann-Low (KL) region with the Mount Fuji submillimeter-wave telescope. The 6′ × 6′ area centered at Orion KL has been mapped with a grid spacing of 1′.5. The intensity distribution of the ³P₂-³P₁ line is found to be similar to that of the ³P₁-³P₀ line; these lines are rather weak toward Orion KL, while they are both bright at Orion KL's northern and southern positions. The excitation temperature determined from the intensity ratio between the ³P₂-³P₁ and ³P₁-³P₀ lines ranges from 40 to 110 K. The excitation temperature is not enhanced toward Orion KL, whereas it tends to be high in the vicinity of θ¹ Orionis C. These results indicate that the C I emission arises from a photodissociation surface illuminated by strong UV radiation from θ¹ Ori C. The relative reduction in the C I intensities toward Orion KL is found to originate from a relatively low excitation temperature rather than from the depletion of the C I column density. The origin of the low-excitation temperature of C I toward Orion KL is discussed in terms of a radiative transfer effect.