H2O+ MOLECULES IN COMET HALE-BOPP

The WIYN, Hydra data on Comet Hale-Bopp show that molecular spectral features of ionized water are more boadly distributed and much more asymmetric than the forbidden Oxygen red auroral line. To illustrate this point, the intensity in the 6198A water plus line was extracted from the 1997 March 16 data and converted into a simulated image. In this "HydraPak Image" the line intensities are converted to a magnitude and then, along with fiber coordinates, read into the "mkobject" task in the IRAF package "artdata" where they are introduced into a 512x512 pixel image as if they were stars. A one pixel full width at hafl maximum, Gaussian point spread function (default) was used. The data shown here are the averages of the six useful frames from this night. The full range of data numbers in the image is 0 to 208000. In the .GIF pictures below various thresholds are used

.....In this first rendering we display only the bottom 0.5 % of the data, intensity numbers from 0 to 1000. The ionized water is easily detected even at the 22.5 arc minute outermost ring which corresponds to a distance from the nucleus of about 350,000 km, similar to the distance from the Earth to the Moon.

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. Note that on this night one of the fibers in the 6 arc minute ring (the third ring inward) refused to deploy; Hydra has a mind of it's own. Also, the distribution of fibers in the 15 and 22.5 arc minute rings (the two outermost rings) is neither even nor perfectly circular. This is an artifact of distribution of fibers around the MOS port on WIYN and the fiber/button proximity restrictions of the fiber assignment code.

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....Here we display data numbers between 0 and 50,000 which serves to emphasize the strong asymmetry of the H2O+ . In these pictures North is at the top, East at the right. Astronomical "Position Angles" are measured from North through East, South, West and back to North (clockwise in these images) 0 through 360 degrees. The Position Angle of the "Anti-Sun", the nominal direction of a comet's ion tail, was 349.6 degrees on this date.

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..... Here we zoom in X4, and display the full data range 0 to 208000. Recall that the variation with Position Angle of the [OI} 6300A feature was less than a factor of two whereas in the 6 arc minute ring of points, the outermost ring in this frame, the variation difference between Sunward (down) and tailward (up) is a factor 16. The neutral Oxygen had completely disappeared into the terrestrial airglow (faint aurorae which are always present at some level) at the 15 and 22.5 arc minute rings. Cometary 6198 is easily detected above sky background at the outermost rings, particularly in the anti-Sun direction.

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A quantitative display of the H2O+ distribution

Click on the above graph to display a fulsized Postscript plot of the radial and P.A. variation of the H2O+ molecule. Out to a nuclear distance of abourt 105 km, the Sunward and Anti-Sun directions are roughly the same, but beyond about 2 x 105 km in the Sunward direction coupling to the Solar Wind takes over and sweeps the molecular ions away quite dramatically.

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