Zolt Levay at his alma mater: Indiana University's Kirkwood Observatory (Image courtesy K. Kalinowski)

Heritage Spotlight:
Zolt Levay
STScI

My first experience with the planetary nebula NGC 6369 was a few years ago, when astronomer Howard Bond asked me to help him put together a color image from some Hubble data he had made. He was working on a large study of the central stars of planetary nebulae. We had two images available, taken through filters of different colors (broad bands of visible/green-yellow and near-infrared/reddish). These images provided the information Dr. Bond needed to study the star at the center of this nebula.

We were able to produce a color composite image, though it was not spectacular. The image did hint at some interesting structures but we were not able to show these with a full color range like we have been able to do with other nebulae. In addition, some of the nebula "fell off" the edge of the camera's field of view because the observations were aimed at the central star rather than the nebula as a whole.

At that time I thought it would be interesting and fun to make Hubble observations that would show this object with a greater range of subtlety and color, and hopefully to see more detailed structure. Through the Hubble Heritage project we were able to get some additional Hubble observations a few years later. This time we used filters that isolated the light of specific chemical elements: Nitrogen, Hydrogen, and Oxygen. We knew from studies of other nebulae that much of the light probably was being emitted by these elements. We planned exposures that would produce the best images of the nebulosity. We also pointed the telescope so the whole nebula fell within the field of view of the camera.

Levay at RIT Reception (Image Courtesy of J. Hayden)

The result was certainly worth the effort! By combining the new (narrow-band) data in separate colors and judiciously adjusting brightness and contrast of the separate images, we have been able to tease out a lot of interesting detail. Swirling shapes show up in the "hole" just surrounding the central star. In the brighter main ring, "fingers" of material point toward the center. And farther out, fainter clouds appear, about twice as far from the central star as the main ring. Contrasting colors resulting from emission of light from different elements and different physical conditions at various places in the nebula enhance and highlight these features.

Our goal in making this image was to show a lot of detail in the entire nebula. One thing that's missing is a representation of the great variation of brightness that exists in reality. While our eyes are able to see a vast brightness range in the same scene, no picture technology can do as well, neither electronic nor print. In reality, the main ring is much brighter than the reddish inner swirls and outer wisps. By adjusting the contrast over the entire image we are able to show all of these features in a single image, but we did have to suppress the very large brightness range.

- Zolt Levay(STScI)