When the scientists combined the light from two 8-meters
telescopes with MIDI, they could simulate the resolving power of
a telescope with a diameter of about 100 meters. These
observations gave a "visibility function," which measures how
resolved a source is: A visibility of 1 happens when a source is
completely unresolved while lower visibilities indicate
increased resolution. For HD 69830, the scientists did not
resolve the star itself, but did resolve the dust emission, as
the visibility clearly does not match the pattern of an
unresolved source (dashed blue line). The levels of dust
emission vary in the wavelength range covered in the observation
(8-13 microns, a region of the mid-infrared spectral range), and
this variation can also be seen in the visibility function.
These results show that the dust lies between 4.7 and 224
million miles (7.5 and 360 million km) from the star (0.05 to 3
times the Earth-Sun distance).