Spectroscopy of Perseid Meteors with an Image Orthicon

An image orthicon technique for recording meteors, developed some years ago by Hemenway at the Dudley Observatory, has recently been used at the Springhill Meteor Observatory, Ontario, for the recording of meteor spectra and combined with three other observational techniques—meteor radars, spectrographs, and a team of visual observers. Fifteen meteors, observed with the image orthicon during the August campaign in 1969, are here discussed out of a total of more than forty. Apparent visual magnitudes range from −1 to +3 and all 14 Perseid spectra in this group exhibit the oxygen green line at 5577 Å as well as other atomic lines normally found in the spectra of members of this shower. At the beginning of their trails all meteors show either a strong continuum, or evidence of band structure where the 1st and 2nd positive systems of N2 have been identified with reasonable certainty, while the first negative systems of N2+ and O2+, and the visible system of OH, are possible contributors.Measures of the 5577 Å line indicate a height spread from 120 to 95 km with a maximum near 106 km. After initial formation the intensity of this line increases for 0.2 to 0.5 s, after which it decays over periods up to 2 s. The decay constant for the 1S metastable state of neutral atomic oxygen is 0.76 s−1.The two chief advantages of the image orthicon technique are: its ability to record meteor spectra down to fainter thresholds of luminosity than in the case of conventional spectrography, and the time-resolution given by a recording of 15 complete frames per second.