The principal characteristics of the eclipsing 
Aurigæ
star system can be reproduced by assuming that the optically unseen
secondary is a disk of gas and dust which is in centrifugal balance
in the radial direction and is hydrostatically supported perpendicular
to its midplane.
Several of the basic characteristics including
ingress time, egress time, and the general flat shape of the minimum are
well accounted for. The geometry of the eclipse implies that the disk
midplane is tilted by < 3
from the line of sight.
The wavelength-independence of the observed eclipse
depth in the visual and near-IR provides
important constraints on the properties of the disk.
This colorlessness implies that the
particles responsible for the bulk of the opacity of the disk are
m in radius. If, in contrast, an ISM particle distribution
were assumed, the eclipse would be much deeper in the blue
than in the red and the near-IR. This conclusion is
stronger and more quantitative than that of Kopal (1971), who also
noted that the grayness of the eclipse implies large particles.
Unless particles of radius 
m
are almost totally absent from the secondary, the scale height at
the outer edge of the disk must be quite small, 
of
the disk's radius. The low
ratio of the scale height to the disk's radius lends some support to
the high-mass model of the 
Aurigæ system.
Our analysis assumes that the gas and dusk in the disk are well mixed. If instead virtually all of the particles in the disk are settled into a significantly thinner dust zone, the secondary could present a sharp-edged profile that produces a colorless eclipse even with an ISM opacity law. However, even a small quantity of submicron-sized dust remaining well above the midplane would color the eclipse.
Our model can produce a significant mid-eclipse brightening only if the
optical depth of the disk is small.
A central hole can increase the magnitude of this mid-eclipse brightening.
However, the duration of the model's mid-eclipse brightening
is longer than that observed. In addition, a model disk optically
thick enough to reproduce the mid-eclipse brightening in single-color
data would only produce a ``gray'' eclipse if virtually all
the particles in the disk are much larger than 5 
m in radius.
Absorption lines seen during and immediately after the F star eclipse are probably produced by a thin layer of gas in the outer portion of the disk companion secondary which expands when it is heated by radiation from the F star and contracts when it is shielded.
The above analysis demonstrates that the 
Aurigæ disk
is well-modeled
by a gas/dust disk with a scale height at its outer edge that is
3% of the disk's radius. Such a disk contains particles
characteristically much larger than
interstellar dust. Our results will provide more valuable information on the
process of planet formation when HIPPARCOS parallax measurements become
available. Once the distance to the system is known, the mass and evolutionary
state of the primary will be better understood (Webbink 1985). The masses of
the components and the geometry of the 
Aurigæ system will
then provide a lower bound on the maximum size of a (quasi-) stable
circumstellar disk within a
binary system of known dimensions. If the system turns out to be young
(Carroll et al.
1991), then the disk properties that we have derived
become directly applicable to models of protoplanetary disks. If
the 
Aurigæ disk was
produced by recent (
years) mass transfer (Eggleton and Pringle 1985), then the lack of
small grains would imply that rapid grain growth can occur within circumstellar
disks and pre-planetary processes may also occur in this context.
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