Hubble sees change in gas shell around Nova Cygni 1992 7/07/1995
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.
Go to full text
Click here to return to the Stars' topics
Image Credit: F. Paresce, R. Jedrzejewski (STScI) NASA, ESA.  

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 meanradius of the shell has increased by 0.0372" (arc seconds). Radial velocity measurements show that the true expansion velocity is about 970km/s.

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 located in the summer constellation Cygnus the Swan. Return to top of page