The Caldwell Objects

away" stars escaped the confines of the Orion
Nebula complex. Ronnie Hoogerwerf (Leiden
Observatory, the Netherlands) and two colleagues
arrived at this conclusion after perusing
ultraprecise astrometry from the Hipparcos
satellite to investigate the motions of two of
Orion's best known "runaway" stars, Mu (μ)
Columbae and AE Aurigae, and of Iota (ι)
Orionis, a lower-velocity binary star whose two
components are in a highly elliptical mutual
orbit. This distinctive foursome, the astronomers
say, is just what the binary-binary encounter
scenario is most likely to produce.
Nowadays, when night falls and Auriga rises,
we can see AE Aurigae — a variable star that
fluctuates erratically between magnitudes 5.8 and
6.1 — burning among the gossamer filaments of
IC 405 (Caldwell 31). Photographic and kinematic
evidence confirms that AE Aurigae did not
condense from the surrounding nebula (as most
hot, young stars associated with nebulae have
done) but is rushing through it like a woman
running down a dark, cobwebbed hall with a
candle. As the woman moves forward, any
cobwebs before her will become illuminated by
the approaching light, while those left clinging to
the walls behind her will eventually dip back into
the shadow of darkness. Likewise, AE Aurigae
will continue to light up IC 405 for perhaps
another 20,000 years, after which the light
reflecting off IC 405 (or exciting its gases) will
fade to near invisibility. Before it leaves the
nebulous region, though, AE Aurigae will greatly
alter the dusty clouds that surround it.
Spectroscopic observations have shown the
bright nebula to be incredibly tenuous,
containing only 1,000 or so particles in every
cubic centimeter. So, as the star "runs" through it,
the pressure of starlight from AE Aurigae will
push aside the surrounding gas just as our
running woman would sweep away any cobwebs
before her.
31
In a 1954 paper titled "The Radial Velocity of the
Flaming-Star Nebula, IC 405," Nicholas U. Mayall
(Lick Observatory) writes, "The galactic diffuse
nebula IC 405 was discovered in 1892, first by J.
M. Schaeberle, and then by M. Wolf and E. von
Gothard, during photography of Nova Aurigae
1891." Wolf considered the inner structure of IC
405 on his photographs to be remarkable. Writing
in a 1903 issue of Monthly Notices of the Royal
Astronomical Society, he described the involved
6th-magni-tude star as "a burning body from
which several enormous curved flames seem to
break out like gigantic prominences." He also
thought it would be of interest for spectroscopists
to observe this "flaming star." Thus did the nebula
receive its name.
In photographs IC 405 is quite enormous. A
1°-wide pool of dust and gas, oriented southeast
to northwest, surrounds AE Aurigae, though the
star appears to rest on the middle of its
southwestern edge. A faint, l°-long extension of
feebly glowing gas runs south of the brighter
component's western side. Overall, IC 405, as
recorded on the deepest photographs, looks like a
bridal veil attached to a headpiece, or like Italy
without the "toe" of the "boot."
The Caldwell Objects 123