SIMBAD references

We have measured the gas temperature in the IC 63 photodissociation region (PDR) using the S(1) and S(5) pure rotation lines of molecular hydrogen with SOFIA/EXES. We divide the PDR into three regions for analysis based on the illumination from γ Cas: sunny, ridge, and shady. Constructing rotation diagrams for the different regions, we obtain temperatures of T_ex = 562_–43⁺⁵² K toward the ridge and T_ex = 495_–25⁺²⁸ K in the shady side. The H₂ emission was not detected on the sunny side of the ridge, likely due to the photodissociation of H₂ in this gas. Our temperature values are lower than the value of T_ex = 685 ± 68 K using the S(1), S(3), and S(5) pure rotation lines, derived by Thi et al. using lower spatial resolution ISO-SWS data at a different location of the IC 63 PDR. This difference indicates that the PDR is inhomogeneous and illustrates the need for high-resolution mapping of such regions to fully understand their physics. The detection of a temperature gradient correlated with the extinction into the cloud, points to the ability of using H₂ pure rotational line spectroscopy to map the gas temperature on small scales. We used a PDR model to estimate the FUV radiation and corresponding gas densities in IC 63. Our results shows the capability of SOFIA/EXES to resolve and provide detailed information on the temperature in such regions.