Abstract
A photographic Fabry-Pérot interferometer was built for the University of Maryland's 20-in. telescope for the study of the radial velocities of diffuse emission nebulae. Observations of S101, S112, IC5146, NGC7380, NGC281, and IC1795 were made and radial velocities at many points within each nebula were determined with an estimated error of ±3 km/sec. Average heliocentric radial velocities were obtained for each nebula and they agree well with those found by other observers.
For S112 and IC5146, a systematic difference of 6–8 km/sec in the radial velocities between the east and west sides of the nebulae was observed. This phenomenon is attributed to the ‘braking’ effect of cold gas which appears to be associated with the western side of both nebulae.
Ring half-widths were obtained for S112, IC5146 and NGC281, and found to be consistent with expansion velocities of 5 km/sec or less. For IC5146 the average Doppler temperature is only 5500±1000 K, which indicates an even lower electron temperature.
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Williamson, R.A. Internal radial velocities of some selected small diameterHii regions. Astrophys Space Sci 6, 45–59 (1970). https://doi.org/10.1007/BF00653619
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DOI: https://doi.org/10.1007/BF00653619