Kimball Staples & Nephi Thompson & Dr. J. Ward Moody, Physics and Astronomy

In March 1996, Dr. J. Ward Moody and Dr. Clark Christiansen obtained a series of approximately 120 CCD (solid state electronic) images of Comet Hyakutake. The images were taken at the National Optical Astronomy Observatory on Kitt Peak, near Tucson, Arizona. The large angle Buffell- Schmidt Telescope that was used is one of the best comet-viewing telescopes in the world because of its expanded field of view. The data obtained is the most extensive coverage of a comet tail to date with a modern solid-state detector.

A CCD (Charge Coupled Device) is a thin wafer of silicon divided into a grid of squares. Each square produces an electric current when struck by photons. Images are obtained by analyzing and graphing the current produced by each square. A CCD has a greater sensitivity to light and produces images with greater resolution than traditional photographic plates. But CCD data must be analyzed and reduced before usable images are obtained, a very time intensive process.

To learn about CCD’s and how to reduce the data, we met three times a week with Michael Rice, a graduate student in astronomy. He first taught us the general theory of CCD’s from a solid state physics perspective. Then he taught us about the specific CCD in the Buffell-Schmidt Telescope on Kitt Peak. We also took a trip to the Kitt Peak Observatory to help with an observing run and to learn about the equipment. For four nights, we helped Dr. Moody to collect and to store data to bring home to Provo for further study and analyzation. After we had an understanding of the data acquisition, Michael taught us how to use IRAF, an astronomical image manipulation, reduction and analyzation software package.

IRAF is the industry standard for astronomical image software. It allows the data to be corrected and assembled into high resolution images. We continued meeting three times a week with Michael and learned how to use the various subroutines by reducing some earlier data. When we were confident that we understood how to use IRAF, we began to work on the comet data.

To assemble the frames into a complete image of the comet, we needed to equalize each frame so that the image would be smooth and have a uniform brightness. We first corrected each frame for bad pixels, background noise, cosmic rays and amount of light coming from the sky. This was done by comparing multiple exposures, flat-field and background frames with each frame and subtracting the difference from the frame. When we finished, each frame was ready to be assembled into a photo mosaic.

The most challenging part of assembling the frames was rotating them. As the frames were taken throughout the night, the earth rotated and the orientation of the comet changed. The frames needed to be rotated before they were assembled so that our final image would be correct. We used spherical trigonometry to calculate the angle of rotation for each frame and used the IRAF rotation subroutine to reorient the frames. This was the most time-consuming part of the image reduction because the angles needed to be exact. We had to redo many of the frames until they were perfectly aligned.

After correcting and rotating the frames, we compared adjacent frames and calculated the overlap so that there would be no seams or rough edges. Occasionally, we had to add to or subtract from the frame so that the comet image was continuous. Finally, we pasted each frame into a huge composite image. Unfortunately, our final image was not perfect the first time. We spent a lot of time evaluating and correcting our work until we were satisfied.

The final image showed some fascinating things about the comet. Unlike most comets, Comet Hyakutake’s head is very small when compared to its relatively long tail. Comet researchers are excited to study our image and understand why Hyakutake is different. Perhaps the most exciting, though, is an unusual clump of material located about halfway down the tail. This clump is darker and more active than the surrounding gases and dust. Most comet tails show a relatively continuous distribution of matter and an absence of clumping. Researchers are very eager to analyze our image which will hopefully lead to a better understanding of comet tail dynamics.

The final image will be published in a refereed scientific journal and was also given to the National Geographic Society who expressed interest in our research.