Astronomers at MMTO Capture Panetary Nebula in Glowing Detail

Astronomers testing a new near-infrared camera on southern Arizona’s
6.5-meter (21-foot) MMTO telescope have produced a sharp, detailed image of
an aged planetary nebula basking in the light of its several-thousand-times
brighter dying central star.

It is the most detailed wide-angle picture yet taken using the large
telescope’s unique adaptive optics system, a technique that removes
atmospheric blurring.

Astronomers from the University of Arizona’s Steward Observatory and Center
for Astronomical Adaptive Optics made the picture of Planetary Nebula IC
2149 from exposures taken at the UA/Smithsonian MMT Observatory on
8,550-foot Mount Hopkins, Ariz. The picture can be downloaded at
http://kalhjasse.as.arizona.edu/~payoung/IC2149.html

The planetary nebula, a cloud of gas and dust shed from a dying star, is
3,600 light-years away and 1.5 trillion miles (2.5 trillion kilometers)
across.

The observers used UA astronomer Donald W. McCarthy’s near-infrared camera
ARIES to search for specific gases in the star’s debris. They took images in
three infrared colors of light, then combined them into a single false-color
image.

While astronomers took the images, the large telescope’s secondary mirror
changed its shape thousands of times each second to compensate in real-time
for atmospheric turbulence that distorts starlight. The MMTO’s ultra-thin,
2-foot-diameter secondary mirror focuses light as steadily as if Earth had
no atmosphere.

The resulting images demonstrate two benefits of the MMTO’s adaptive optics
system, McCarthy and UA astronomy graduate student Patrick A. Young said.

First, the images are about three times sharper than images obtained with
UA’s NICMOS cameras on the Hubble Space Telescope, and they are as sharp as
Hubble images at shorter visible wavelengths.

Second, the sharper images show faint structure close to bright objects like
stars in much greater detail. The image of IC2149 shows a contorted mixture
of gas and dust several thousand times dimmer than the star itself. The halo
around the star is the size of solar systems.

The team selected Planetary Nebula IC 2149 for the engineering tests of
ARIES from 10 candidate targets during their telescope time last October,
Young said.

“What you are seeing here is a star, a little less massive than the sun,
that has used up all the fuel at its nuclear-burning core,” Young said.
“Unable to produce energy, the core starts to contract, and turns into a
ball of carbon and oxygen the size of the Earth. This gravitational
contraction releases a lot of energy, and that causes the star to shed its
outer atmosphere. The material we are actually seeing in the picture is the
gas and dust being lit up by the light from the central star.”

Their observations suggest that all of the molecular hydrogen in the nebula
has been destroyed by radiation from the central star, leaving only ionized
hydrogen. Added to other evidence, this indicates that the nebula is several
thousands of years old, Young said.

Most planetary nebulae disperse and vanish in less than 10,000 years. The
gas and dust ejected by the dying star contain heavy elements from which
future planets may form.