IC 63 is a reflection nebula associated with the B0.5 IVpe star gamma Cas (HD 5394), which lies at a distance of approximately 230 pc. The projected distance between IC 63 and the star is 20', corresponding to 1.3 pc. Due to the proximity of the star, the cloud is exposed to approximately 650 times the mean galactic ultraviolet radiation field. The molecular lines are narrow (approx. 1 km/s), indicating the absence of shocks that might otherwise have influenced the chemistry. The cloud is also much easier to study and less confused than the well known PDRs like M 17, which is very distant and highly extinguished or NGC 2023, which has an unfavorable geometry for viewing the interaction zone edge-on. All of this makes IC 63 one of the nearest PDRs, and an ideal prototype to study PDR chemistry.
A picture of this source is here. Actually, IC 63 is the lower left "blob" in this IRAS 100 micron image. This image was created using the IRAS server in Groningen
We have observed IC 63 in a number of molecular transitions. Click here to see maps in CO 2-1 (top) and 3-2 (bottom). These observations have been done at the Caltech Submillimeter Observatory on Mauna Kea, Hawaii.
The observations were then analysed using a radiative (de)excitation code to convert the observed emission line intensities to molecular column densities. Most molecules are slightly less abundant in IC 63 than in dark clouds, due to the strong UV radiation.
Chemical calculations have been performed in order to model the observed molecular column densities. This figure shows the calculated abundances of the molecules as function of the depth into the cloud. In general the calculated column densities match the observations quite well.
This is work I do together with Ewine F. van Dishoeck (my thesis supervisor) in Leiden, and John Black in Tucson, Arizona. For the chemical models I also collaborate with Marco Spaans here in Leiden.
