jrasc june 1998 final - The Royal Astronomical Society of Canada

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jrasc june 1998 final - The Royal Astronomical Society of Canada

Research NoteA PERSEID METEOR SPECTRUMby Jirí Borovicka 1 and Edward P. Majden 21 Ondrejov Observatory, and 2 RASC Victoria CentreElectronic Mail: borovic@asu.cas.cz, epmajden@mars.ark.com(Received November 14, 1997; revised January 26, 1998)Abstract. The spectrum of a Perseid meteor photographed from Courtenay, British Columbia, has been analyzed. Forty spectrallines were identified, including the green forbidden line of oxygen at the beginning of the meteor track. As in other fast meteors, twospectral components with apparent effective temperatures of 4500 K and 10,000 K, respectively, are present in the spectrum. The linesof the high temperature component are particularly conspicuous in flares near the end of the trajectory. That is tentatively explainedby the increased strength of the shock wave, but the fact that the lines of the high temperature component are optically thin is alsoimportant.Résumé. Le spectre d’un météore Perséïde, photographié à Courtenay, Colombie Britannique, a été analysé. Quarantes lignes spectralesont été identifiés, y compris la ligne verte interdite d’oxygène au début de la trajectoire du météore. Ainsi que pour d’autres météoresrapides, nous retrouvons deux composants gazeux dans le spectre, avec des températures respectivement de 4 500 K et 10 000 K. Leslignes du composant à haute température sont particulièrement évidentes dans les flambées au bout de la trajectoire. Une explicationtentative de ce phénomène pourrait être la croissance de la force des ondes de choc, mais le fait que les lignes du composant à hautetempérature sont minces du point de vue optique est aussi important.SEMA meteor spectroscopy program has been carried out by one of us(EPM) in Courtenay, British Colombia, since 1972. The programresulted in photographs of several meteor spectra of various quality.Here we present the results of an analysis of one of the best observationsobtained, the spectrum of a Perseid meteor acquired on August 13,1986.The spectrum was secured during an exposure of 10 minutesduration starting on August 13, 1986, at 01:15 PST (09:15 UT). Thecamera was a modified F-24 aero with a 2.9/8-inch Pentac lensequipped with an objective prism. A 4 5 inch sheet of KodakRoyal Pan 4141 film was used to record the observation. The meteorwas photographed from one station only and no data on the trajectoryare available.The spectrum is reproduced here in figure 1. A sudden increaseof brightness occurred on the trajectory, followed by almost constantlight intensity until the onset of two bright flares near the end. Inaddition, a single line is present at the very beginning, where otherlines are still invisible. It is the forbidden line of atomic oxygen at5577 Å, with its typical behaviour as described by Halliday (1960).The spectrum was measured by the two-axis microdensitometerat the Ondrejov Observatory of the Czech Republic. The spectra ofthe stars And and And, recorded on the same negative, wereused to determine the spectral sensitivity of the instrument. Froma comparison with the stellar spectra and from consideration ofthe different angular velocities, the meteor maximal magnitudewas estimated to be –5 visual and –6 photographic.The photometric tracing of the spectrum for the terminalflare is presented in figure 2. The spectral dispersion was 210 Åmm –1 at 4000 Å and 500 Å mm –1 at 5000 Å. The intensity scale wascorrected for the spectral sensitivity of the instrument. At 4600–5000Fig. 1 — Scanned image of the Perseid meteor spectrum negative. Themeteor moved from the top to the bottom. Wavelengths increase from leftto right. Spectra of the stars And (left), And and ν And are visible belowthe meteor.June/juin 1998 Journal of the Royal Astronomical Society of Canada, 92:153–156, 1998 June153

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