Description |
We propose to perform deep integrations for a significant detection of the 13CII and 13CI hyperfine transitions towards five PDRs where previous observations showed marginal, inconsistent or particularly puzzling results. These included anomalous hyperfine ratios and strong variations of the fractionation within one source. The observations will measure the absolute C+ fractionation, they will allow to distinguish the effects of isotope-selective photodissociation and chemical fractionation, and constrain the total isotopic ratio of 13C to 12C. |