The Postminimum Spectrum of R Hydrae.
Paul Willard Merrill · The Astrophysical Journal · 1952
Five spectrograms, dispersion to A/mm, were obtained during the time when the light was increasing after minimum. Near minimum, ground-level lines of Ca I, Al r, and K I became extraordinarily intense. Bright hydrogen lines appeared in low intensity about 50 days after minimum, with displacements algebraically greater than those measured previously at maximum light. The emitting hydrogen atoms appear to have an outward acceleration until they disappear before the next minimum. The dark lines, on the other hand, yield about the same velocity shortly after minimum as they do at maximum.