Collision Broadening and Shift in the 6573 Line of Calcium

Abstract

The collision broadening and shift of the line Ca 6573 A due to an external pressure of helium have been measured. The half-intensity damping width of the line was found to be 1.42 ± 0.07 × 10 ⁻²⁰ cm ⁻¹ per atom per cc of helium, and the shift 0.19 ± 0.05 × 10 ⁻²⁰ cm ⁻¹ per atom per cc of helium towards the violet. The ratio of broadening to shift is 7.5. This result is shown to be consistent with the hypothesis that short-range repulsive forces between calcium and helium atoms are predominantly responsible for the broadening and shift. No deduction about collision broadening and shift in stellar atmospheres can be made from these laboratory results, but it is suggested that a study of more highly excited lines may yield astrophysically relevant results.