Robert R. McMath

Solar Spectroscopy with a Cashman Cell

A description is given of a long-focus all-reflecting spectrometer of the Pfund type which has been designed and constructed at the McMath-Hulbert Observatory for initial application to the infra-red solar spectrum. The detectors employed thus far are two Cashman cells that permit the recording of the solar spectrum between 1.0μ and 3.6μ with high resolution. The amplifier was designed and constructed by W. Wilson. Radiation from overlapping orders is effectively eliminated by a pre-dispersing unit. Two plane reflection gratings, ruled 600 lines/mm and 200 lines/mm, are used for the regions 1.0μ–2.5μ and 2.5μ–3.6μ respectively. Observed line separations indicate that approximately 80 percent of the theoretical resolving power has been attained.

THE DOPPLER EFFECT IN AN ERUPTIVE PROMINENCE

In determining the characteristics of prominence motion with the spectroheliograph the question of the possible deformation of the images by radial velocities of the internal structure is always present. This is of peculiar interest in prominences of the eruptive class. In the design of the spectroheliograph of the tower telescope at Lake Angelus we have included means whereby the chromospheric line used to make the photographs may be shifted a known amount from the second slit. This is done by observing an emission line of mercury or neon produced by a fixed slit and observed with a microscope. To test the effect of a shift on the form of a prominence the line was thus artificially displaced 1 A to the violet, then 1 A to the red on pairs of successive exposures (frames) of the motion-picture camera at intervals during the eruption. If any large radial velocities were present they would appear as changes in the prominence structure which these frames reveal.