Pelican Nebula Ionization Front

Image: The Pelican Nebula Ionization Front

The North America/Pelican nebula complex, located a few degrees East of the bright star Deneb in the constellation of Cygnus the Swan, is one of the most recognizable and most photographed nebulae in the sky.   These clouds of gas and dust get their names from their distinctive shapes when viewed in wide-field telescope images. This image, showing the cloud next to the "neck" and "body" of the Pelican, was obtained at the National Science Foundation's Mayall 4-meter telescope at Kitt Peak National Observatory near Tucson, AZ, using the Mosaic CCD camera.  Narrow-band filters were used to isolate the red emission lines of hydrogen and singly-ionized sulfur.  This image reveals many previously unseen details - including evidence for recent star formation -- in the Pelican nebula portion of the complex.

In most views, the Pelican and the North America nebula located two degrees east, look to be distinct objects separated by a dark lane extending from where the "Caribbean Sea" and "Atlantic Ocean" ought to be located.  However, radio wavelength studies have shown that these two nebulae trace the Eastern and Western parts of a single nebula that is over two degrees in extent.  The dark lane is a giant molecular cloud seen in silhouette against the background nebula, which hides the massive stars responsible for its creation.  This complex of nebulosity, young stars, and molecular clouds is located about 600 parsecs (1,800 light years) from Earth.

The Pelican nebula wraps around another molecular cloud located northwest of the complex.  The cloud surface is ionized and ablated by intense ultraviolet light produced by the hidden massive stars.  Denser gas retards the advance of this ionization front, allowing portions of the molecular cloud to survive in their shadows.  Sometimes, such clumps become detached from the main cloud.  Several such clouds can be seen South of the main-cloud edge.  In other places, the clumps are still attached to the main cloud, form the so-called "elephant trunks" or "pillars." Such pillars and detached cloud they like arrows toward the source of illumination.


Star formation continues in the dusty and opaque interior of the cloud.  Occasionally, the high velocity streams of gas ejected by young stars burst into the HII region.  Such a jet of gas emerges from the head of the prominent elephant trunk in the lower-left, indicating the presence of an invisible young star.  An embedded infrared source in the main cloud drives a supersonic outflow into the nebula towards the South. As this chain emerges into the lower density surroundings, it is deflected towards the West, indicating that there is an outflow of plasma from the core of the HII region.  This image reveals about a dozen shocks powered by young stars embedded in the clouds adjacent to the nebula. North is up and West is to the right.

Image Credit: University of Colorado, University of Hawaii and NOAO/AURA/NSF
Source: NOAO/Bally
Contact: Douglas Isbell

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