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NOAO Newsletter - NOAO Highlights - March 2000 - Number 61


Supernova 1987A Dings the Ring

Bruce Bohannan

A team of astronomers led by Patrice Bouchet (CTIO), which includes Stephen Lawrence, Arlin Crotts, Ben Sugerman, Robert Uglesich (Columbia), and Stephen Heathcote (CTIO), used a new "tip/tilt'' imaging camera at the CTIO 4-m Blanco telescope to discover a new brightening of the circumstellar ring around Supernova 1987A in the Large Magellanic Cloud. This activity indicates that supernova ejecta have finally begun to collide with the shell of gas puffed out by the star earlier in its lifetime --- the beginning of a critical phase in the formation of a supernova remnant that has never before been witnessed.

A "hot spot" that appeared in the circumstellar ring around SN1987A in 1997 was believed to be the first impact of supernova ejecta. No other active sites had been observed until 25 December 1999, when the Bouchet et al. team first observed a new hot spot. The new hot spot is about the same brightness as the first was when it was originally found. Other, fainter impact sites are also present in their observations. They Bouchet team also found that the original hot spot had brightened significantly since their last observation over a year ago.


Caption: The increasing brightness of the hotspot in the ring around SN1987A discovered in 1997 and the new hot spot to the southeast are readily evident in the difference between the 1998 October and 1999 December observations of Bouchet et al. (left panel). The right-hand panel is the image made in HeI 10830A on 25 December 1999. Frames are ~ 16 arcsec square, with north up and east to the left.

The basic spatial resolution of the images was enhanced by use of tip/tilt image motion compensation at the Blanco telescope. Maximum entropy deconvolutions conducted by the Bouchet et al. team clearly show the new hot spot and reveal fainter, possible new hot spots. The significance of the newly discovered hot spots is that they are not confined to a single location, but are distributed around the circumstellar ring. The distribution around the ring indicates that a large fraction of the material ejected from the supernova is finally colliding with the circumstellar ring, instead of a fast-moving "bullet" of ejecta making a single hot spot. If so, this is the beginning the long-awaited formation of a supernova remnant around SN1987A. Other teams making follow-up observations with the HST in late January and early February have confirmed the new hot spot (IAU Circulars 7359 and 7360, New York Times February 15 issue) and found a number of other fainter new impact sites, which are present in the CTIO data at a subtle level.


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