The Caldwell Objects

with a CCD camera — discovered a supernova
(Supernova 1993Z) just 15" west and 42" south of
NGC 2775's nucleus. (The program ended in
December 1994.) The "guest star" shined at about
14th magnitude in red light. Spectra obtained two
days later with the Shane 120-inch reflector at
Lick Observatory revealed that the supernova
was a Type la about four
48
weeks past maximum brightness. Type Ia
supernovae are believed to be explosions, either
of a single white-dwarf star that rapidly acquires
mass from a companion star, causing a runaway
thermonuclear reaction (the majority view), or of
two white dwarfs that have spi-raled into one
another and merged (this view is held by a
minority of astrophysicists).
The Caldwell Objects 193