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focnovt1.txt
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1996-01-12
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HUBBLE SEES CHANGES IN GAS SHELL AROUND NOVA CYGNI 1992
The European Space Agency's ESA Faint Object Camera utilizing the
corrective optics provided by NASA's COSTAR (Corrective Optics
Space Telescope Axial Replacement), has given astronomers their
best look yet at a rapidly ballooning bubble of gas blasted off a
star.
The shell surrounds Nova Cygni 1992, which erupted on February
19, 1992. A nova is a thermonuclear explosion that occurs on the
surface of a white dwarf star in a double star system.
The new HST image [right] reveals an elliptical and slightly
lumpy ring-like structure. The ring is the edge of a bubble of
hot gas blasted into space by the nova. The shell is so thin that
the FOC does not resolve its true thickness, even with HST's
restored vision.
An HST image taken on May 31 1993, [left] 467 days after the
explosion, provided the first glimpse of the ring and a
mysterious bar-like structure. But the image interpretation was
severely hampered by HST's optical aberration, that scattered
light from the central star which contaminated the ring's image.
A comparison of the pre and post COSTAR/FOC images reveals that
the ring has evolved in the seven months that have elapsed
between the two observations. The ring has expanded from a
diameter of approximately 74 to 96 billion miles.
The bar-like structure seen in the earlier HST image has
disappear. These changes might confirm theories that the bar was
produced by a dense layer of gas thrown off in the orbital plane
of the double star system. The gas has subsequently grown more
tenuous and so the bar has faded.
The ring has also grown noticeably more oblong since the earlier
image. This suggests the hot gas is escaping more rapidly above
and below the system's orbital plane. As the gas continues
escaping the ring should grow increasingly egg-shaped in the
coming years.
HST's newly improved sensitivity and high resolution provides a
unique opportunity to understand the novae by resolving the
effects of the explosion long before they can be resolved in
ground based telescopes.
Nova Cygni is 10,430 light years away (as measured directly from
the ring's diameter), and located in the summer constellation
Cygnus the Swan.
Credit: F. Paresce, R. Jedrzejewski (STScI)
NASA/ESA
PHOTO RELEASE NO.: STScI-PR94-06