Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.arcetri.astro.it/~palla/ANDREAIMMAGINI/ISM/NGC7027.txt Дата изменения: Tue Jan 30 14:24:19 2001 Дата индексирования: Sat Dec 22 07:57:44 2007 Кодировка: Поисковые слова: optical telescope

FOR RELEASE: MARCH 19, 1998

PHOTO NO.: STScI-PRC98-11A

STARING INTO THE WINDS OF DESTRUCTION:
HST/NICMOS IMAGES OF THE PLANETARY NEBULA NGC 7027

The Hubble Space Telescope's Near Infrared Camera and Multi-Object
Spectrometer (NICMOS) has captured a glimpse of a brief stage in the
burnout of NGC 7027, a medium-mass star like our sun. The infrared
image (on the left) shows a young planetary nebula in a state of
rapid transition. This image alone reveals important new information.
When astronomers combine this photo with an earlier image taken
in visible light, they have a more complete picture of the final stages
of star life.

NGC 7027 is going through spectacular death throes as it evolves into
what astronomers call a "planetary nebula." The term planetary
nebula came about not because of any real association with planets,
but because in early telescopes these objects resembled the disks
of planets.

A star can become a planetary nebula after it depletes its nuclear
fuel - hydrogen and helium - and begins puffing away layers of material.
The material settles into a wind of gas and dust blowing away from
the dying star. This NICMOS image captures the young planetary
nebula in the middle of a very short evolutionary phase, lasting
perhaps less than 1,000 years. During this phase, intense ultraviolet
radiation from the central star lights up a region of gas surrounding it.
(This gas is glowing brightly because it has been made very
hot by the star's intense ultraviolet radiation.) Encircling this
hot gas is a cloud of dust and cool molecular hydrogen gas that
can only be seen by an infrared camera. The molecular gas is being
destroyed by ultraviolet light from the central star.

THE INFRARED VIEW -- The composite color image of
NGC 7027 (on the left) is among the first data of a planetary
nebula taken with NICMOS. This picture is actually composed
of three separate images taken at different wavelengths. The red
color represents cool molecular hydrogen gas, the most abundant
gas in the universe.

The image reveals the central star, which is difficult to see in
images taken with visible light. Surrounding it is an elongated
region of gas and dust cast off by the star. This gas (appearing as
white) has a temperature of several tens of thousands of degrees
Fahrenheit. The object has two "cones" of cool molecular hydrogen
gas (the red material) glowing in the infrared. The gas has been
energized by ultraviolet light from the star - a process known as
fluorescence. Most of the material shed by the star remains
outside of the bright regions. It is invisible in this image
because the layers of material in and near the bright regions
are still shielding it from the central star's intense radiation.

NGC 7027 is one of the smallest objects of its kind to be imaged
by the Hubble telescope. However, the region seen here is
approximately 14,000 times the average distance between Earth
and the sun.

THE INFRARED AND VISIBLE LIGHT VIEW -- This visible and
infrared light picture of NGC 7027 (on the right) provides a
more complete view of how this planetary nebula is being shaped,
revealing steps in its evolution.

This image is composed of three exposures, one from the Wide
Field and Planetary Camera 2 (WFPC2) and two from NICMOS.
The blue represents the WFPC2 image; the green and red, NICMOS
exposures. The white is emission from the hot gas surrounding the
central star; the red and pink represent emission from cool
molecular hydrogen gas. In effect, the colors represent the three
layers in the material ejected by the dying star. Each layer depicts
a change in temperature, beginning with a hot, bright central
region, continuing with a thin boundary zone where molecular
hydrogen gas is glowing and being destroyed, and ending with a
cool, blue outer region of molecular gas and dust.

NICMOS has allowed astronomers to clearly see the transition
layer from hot, glowing atomic gas to cold molecular gas. The
origin of the newly seen filamentary structures is not yet understood.
The transition region is clearly seen as the pink- and red-colored
cool molecular hydrogen gas. An understanding of the atomic
and chemical processes taking place in this transition region are of
importance to other areas of astronomy as well, including star formation
regions. WFPC2 is best used to study the hot, glowing gas, which is
the bright, oval-shaped region surrounding the central star. With
WFPC2 we also see material beyond this core with light from the
central star that is reflecting off dust in the cold gas surrounding
the nebula. Combining exposures from the two cameras allows
astronomers to clearly see the way the nebula is being shaped by
winds and radiation. This information will help astronomers
understand the complexities of stellar evolution. NGC 7027 is
located about 3,000 light-years from the sun in the direction of
the constellation Cygnus the Swan.

Credits: William B. Latter (SIRTF Science Center/Caltech)
and NASA

Other team investigators are: J. L. Hora (Smithsonian Astrophysical
Observatory), J. H. Bieging (Steward Observatory), D. M. Kelly
(University of Wyoming), A. Dayal (JPL/Caltech), A.G.G.M. Tielens
(University of Groningen), and S. Trammell (University of North Carolina
at Charlotte).


NOTE TO EDITORS:


A photo and caption are available via the World-Wide Web at:
http://oposite.stsci.edu/1998/11 or via links in:
http://oposite.stsci.edu/pubinfo/latest.html or
http://oposite.stsci.edu/pubinfo/pictures.html

GIF and JPEG images are available via anonymous ftp to oposite.stsci.edu in
/pubinfo/gif/9811a.gif, /pubinfo/gif/9811a.jpg