Publications
of the
MPIfR
Optical & Infrared
Interferometry Group
A.B. Men'shchikov, D. Schertl, P.G.
Tuthill,
G. Weigelt, and L. Yungelson:
Properties of the close binary and
circumbinary torus of the Red Rectangle
Astronomy & Astrophysics, 393, 867 (2002)
Abstract.
New diffraction-limited speckle images of the Red Rectangle in the
wavelength
range 2.1--3.3 µm with angular resolutions of 44--68 mas
(Tuthill et al. 2002) and previous speckle images at 0.7--2.2 µm
(Osterbart et al. 1997, Men'shchikov et al. 1998) revealed
well-resolved bright
bipolar outflow lobes and long X-shaped spikes originating deep inside
the outflow cavities. This set of high-resolution images stimulated us
to
reanalyze all infrared observations of the Red Rectangle using our
two-dimensional
radiative transfer code. The high-resolution images imply a
geometrically and
optically thick torus-like density distribution with bipolar conical
cavities
and are inconsistent with the flat disk geometry frequently used to
visualize
bipolar nebulae. The new detailed modeling, together with estimates of
the
interstellar extinction in the direction of the Red Rectangle enabled
us to more
accurately determine one of the key parameters, the distance D
=
710 pc with model uncertainties of 70 pc, which is twice as far
as the commonly used estimate of 330 pc. The central binary is
surrounded by
a compact, massive (M = 1.2 Msun), very dense dusty
torus
with hydrogen densities reaching n_H = 2.5 x 10^12 cm^-3
(dust-to-gas
mass ratio rho_d/rho ~ 0.01).
The model implies that most of the dust mass in the dense torus is in
very
large particles and, on scales of more than an arcsecond, the polar
outflow regions are denser than the surrounding medium. The bright
component of the spectroscopic binary HD 44179 is a post-AGB star with
mass
M* = 0.57 Msun, luminosity L* = 6000 Lsun,
and effective temperature T* = 7750 K. Based on
the orbital elements of the binary, we identify its invisible component
with a
helium white dwarf with Mwd ~ 0.35 Msun, Lwd
~ 100
Lsun, and Twd ~ 6 x 10^4 K. The hot white
dwarf ionizes the low-density bipolar outflow cavities inside the dense
torus,
producing a small HII region observed at radio wavelengths. We propose
an
evolutionary scenario for the formation of the Red Rectangle nebula, in
which the
binary initially had 2.3 and 1.9 Msun components at a
separation of
130 Rsun. The nebula was formed in the ejection of a common
envelope after
Roche lobe overflow by the present post-AGB star.
You can get this publication ...