The Caldwell Objects

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model for the ellipse is an expanding prolate
ellipsoid (a football with rounded tips). The
football is tilted by about 45° to our line of sight,
with the northeastern tip approaching us and the
southwestern end receding from us. The
outermost regions of the surrounding halo mimic
the shape of the football in the planetary's center.
One unsolved planetary-nebula mystery
involves fast-moving knots of gas called FLIERs
(fast low-ionization emission regions). FLIERs
can be identified in the outer regions
of several planetaries, where they appear as small
knots, generally in pairs on opposite sides of its
central star and often along the nebula's
symmetry axis. In NGC 7662's case the FLIERs
appear to be much younger than their parent
nebula. On the basis of their anomalous chemical
abundances Balick speculates that the FLIERs in
planetary nebulae were probably dredged up
from highly processed material deep inside the
nebula's precursor star, then flung outward like
small spitballs — an astonishing feat, he says, for
a nearly solid star about to become a crystalline
white dwarf. (See my Caldwell 15 essay for more
on FLIERs.)
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NGC 7662's central star is enigmatic in another
way as well; it long has been suspected of being
variable. On 80 different dates between 1897 and
1908, Edward Emerson Barnard found this star
varying between 12th and 16th magnitude. The
periods of greatest brightness, he says, were not
long lasting, and they occurred at irregular
intervals. This variability is controversial among
astronomers, however, and Barnard himself
harbored doubts. "Familiarity with the changing
aspect of a star involved in nebulosity, due to
moonlight, bad seeing, etc., has made me
extremely cautious in the matter." Thus William
Sheehan quotes the famous astronomer in his
biography The Immortal Fire Within: The Life and
Work of Edward Emerson Barnard.
Photographically based magnitude estimates
made since 1934 have shown the Light Blue
Snowball's central star varying from magnitude
11.5 to 13.0, with 12.5 being the average. Some
argue that the apparent variation is merely the
result of atmospheric instabilities, a possibility
Barnard himself hinted at. In his Celestial
HandbookRobert Burnham Jr. suggested that
amateurs with fairly large telescopes try to solve
the controversy. But I am not aware of any
attempts to do so. Therefore I would like to
repeat Burnham's plea and remind amateurs,
especially those with CCDs, that monitoring the
brightness of the Light Blue Snowball's central
star would make a great autumn or summer
project, the results of which would be of value to
the astronomical community.
Having said that, I do not know of any amateur
who has actually seen NGC 7662's central
star with his or her own eye at the telescope.
Certainly a 13th-magnitude star should be discernible
in the large instruments that adorn the
fields at today's star parties. The problem, as I see
it, seems to be that the hole at the center of NGC
7662's "doughnut" is glazed over
Deep-Sky Companions: The Caldwell Objects