Experimental M1 transition rates of coronal lines from Ar x, Ar xiv, and Ar xv

Transition probabilities of three magnetic dipole (M1) transitions in multi ply charged ions of Ar have been measured using the Livermore electron-beam ion trap. Two of the transitions are in the ground configurations of Ar XI V (B-like) and Ar nr (F-like), and are associated with the coronal lines at 4412.4 and 5533.4 Angstrom, respectively. The third is in the excited 2s2p configuration of Be-like Ar XV and produces the coronal line at 5943.73 An gstrom. Our results for the three atomic level lifetimes are 9.32 +/- 0.12 ms for the Ar x 2s(2)2p(5) P-2(1/2)o level, 9.70 +/- 0.15 ms for the Ar XIV 2s(2)2p P-2(3/2)o level, and 15.0 +/- 0.8 ms for the Ar XV 2s2p (3)p(2)(o) , level. These results differ significantly from earlier measurements and a re the most accurate ones to date.