Astron. Astrophys. 336, 648-653 (1998)
Fig. 1 shows contour plots for the resulting images of the Red
Rectangle. The plots appear to be similar at a first look but provide
several detailed features that we describe briefly:
The central region (0.5 arcsec) of the nebula is elongated along a
nearly north-south direction. L' and M images are similar while the
one at 3.3 µm is more elongated and the K image is more
In K band and at 3.3 µm the core of the nebula is
partially resolved into two sources with an angular separation less
than 0.2 arcsec. In Fig. 2, we display the east-west photometric
profiles through the maximum along the north-south direction of each
image (the maxima have been normalized to the same value). The L' and
3.3 µm images have relatively brighter cores (with
respect to the extended component) than the K and M images.
The X shape of the nebula already seen at small scales (0.1 arcsec)
at 0.85 µm and 1.65 µm (Roddier et al. 1995)
is clearly visible in our images. The axis of the cone is oriented
with a P.A. of . The opening angle of the cone
increases with wavelength. The cone is less open
() in the K image than in the M image
(). This is shown in detail in Fig. 3 where
low values of the intensities close to the core are plotted. The image
at 3.3 µm shows that the UIR emission is more prominent
along the walls of the bicone than the continuum. This confirms the
mid-infrared UIR observations of Hora et al. (1996) and is the first
observation of this structure at a wavelength of 3.3µm.
The nebula is not axisymmetric. All images present an asymmetry of
the inner lobes, with the southern lobe being about
50 brighter than the northern one. These images
favour a geometry where the system is tilted a few degrees out of the
plane of the sky causing the northern lobe to be obscured by dust in
the equatorial disk. Table 2 gives estimates of the relative
contribution of the total flux at each wavelength in the core and the
north and south lobes. Fig. 4 shows the geometry used to
calculate these flux contributions.
No stellar binarity appears in any image.
A structure extending to about 0.5 arcsec from the core of the
nebula is present in the eastern direction of the K image. This
structure is also present in the K image of Cruzalèbes et al.
(1996) and in the H image of Roddier et al. (1995). On the other hand
there are no significant east-west features in our L' & M images.
Fig. 1. Contour plots of the intensity of the K (2.22 µm), L' (3.87 µm), M (4.75 µm) and 3.3 µm UIR feature deconvolved images of the Red Rectangle. North is at the top and East is on the left. Contour levels are 2, 1, 0.4, 0.2, 0.1, 0.04 and 0.012% of the total power for each image. Lowest contours are five times the standard deviation of the noise, measured in regions external to the nebula.
Fig. 2. Photometric profiles of the deconvolved images of the core of the Red Rectangle nebula in the direction of the side lobes (PA = ). The vertical intensity scale is arbitrary. Profiles have been normalized to the same maximum intensity. North is on the right hand side. Full line: K image; dash: L' image; dash-dot: M image; dot: 3.3 µm image. Both lobes are partially resolved in K and at 3.3 µm.
Fig. 3. Contour plot of the intensity in the core of the K and M images of the Red Rectangle. North is at the top, east is on the left. In K, the cone seems less open (with a total angle of ) than in M ().
Fig. 4. Geometry used to calculate the relative flux contributions of the core and of the South and North lobes to the total flux. The central core is 0.21 arcsec in diameter while the two lobes cover an area of approximately 1.5 1.5 arcsec2.
Table 2. Relative flux contributions in the Core, the South and the North lobe of the total flux in K, L', M and at 3.3 µm. See Fig. 2 for the geometry description of the extension of the core and the two lobes.
© European Southern Observatory (ESO) 1998
Online publication: July 20, 1998