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Comet Hale-Bopp Spectra Obtained by Urban Amateur Astronomers

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Comet Hale-Bopp Spectra Obtained by Urban Amateur Astronomers

(Hoboken, New Jersey)....Two amateur astronomers, Nick Glumac and Joseph Sivo, obtained a spectra of comet Hale-Bopp in the range 350 nm to 520 nm, under light polluted urban skies near New York City, on April 4, 1997 between 8:00 and 9:00 PM Eastern Time. The observers used a 10 inch Meade LX-200 telescope, an Ocean Optics S200 Fiber Optic Spectrometer (a miniature spectrometer with a linear 2048 CCD pixel array), a novel designed eyepiece-holder/fiber optic coupler, a 15 volt photomultiplier tube (PMT) , and a laptop 486 computer. With this system, less than 1 nm resolution was achieved.

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Comet Hale-Bopp Spectra

The obtained intensity versus wavelength plot clearly shows one CN band, three C2 bands and possibly a C3 feature. The spectrum is quite similar to that obtain by Rauer, et al, presented in the March 28, 1997 issue of SCIENCE, entitled "Optical Observations of Comet Hale-Bopp (C/1995 01) at Large Heliocentric Distances Before Perihelion" and is also similar to the spectrum of comet Halley obtained on March 9, 1986, by the Vega 2 spacecraft presented in the journal ASTRONOMY AND ASTROPHYSICS volume 187 entitiled "Spectrophotometry of Comet P/Halley at Wavelengths 275 - 710 nm from Vega 2".

The experimental procedure was as follows :

A standard 26mm eyepiece was initially used to center and focus the comet nucleus. Then the fiber-optic coupler (a two element lens system) was substituted for the eyepiece. Having the other end of the fiber attached to the PMT, image centering and focu sing on the 10 micron fiber was systematically optimized until maximum signal (read from a voltmeter) was achieved. As altazimuth tracking continued, the spectrometer was then substituted for the PMT. A one minute integration was performed. Immediately following, the telescope was panned to a position 3 degrees to the left of the comet nucleus and a one minute integration was commenced to obtain dark current, sky glow and light pollution effects. Six alternating one minute integrations were performed on the comet nucleus and background sky. To obtain future atmospheric transmission effect corrections, the procedure was repeated on the calibration star Sirius.

The experimental data was processed as follows:

The data from the six runs was smoothed by performing a five pixil running average. The pixel data was then binned by five. The background data was then subtracted from the comet nucleus data. The spectra obtained was then corrected for the spectrometer disperser's efficiency and the detector's sensitivity by measuring the spectra of a calibrated 10 watt tungsten lamp. The data was not adjusted for the transmission characteristics of the telescope's optical glass "corrector plate" nor the two elemen t fiber optic coupler. These corrections would primarily effect the UV portion of the spectra. Also, atmospheric transmission corrections (using the target calibration star Sirius) were not performed at the time of this writing.

The two amateur astronomers are presently developing their own ultra low light level astronomical spectrometer system with thermoelectric cooler. The system is intended to be packaged for advanced amateur and small college astronomy program use.

Both Glumac and Sivo hold doctoral degrees from Caltech in the field of mechanical engineering and are avid amateur astronomers. They presently reside in New Jersey (exits 9 and 14c, respectively).

Nick Glumac
glumac@jove.rutgers.edu

Joseph Sivo
jmsivo@easyway.net


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