[1] The Citadel, Dept Phys, Charleston, SC 29409 USA
[2] Univ Nacl Tucuman, Dept Fis, Fac Ciencias Exactas & Tecnol, RA-4000 San Miguel De Tucuman, Tucuman, Argentina
[3] Natl Res Council Canada, Dominion Astrophys Observ, Herzberg Inst Astrophys, Victoria, BC V9E 2E7, Canada