We present 10 and 20 \mu m images of IRAS 19500-1709 taken with the mid-infrared camera , OSCIR , mounted on the Gemini North Telescope .
An extended circumstellar envelope is detected , with the N band image indicating an elongation in a NE-SW direction .
We use a dust radiation transport code to fit the spectral energy distribution from UV to sub-mm wavelengths , with a detached dust shell model .
A good fit is achieved using dust composed of amorphous carbon , silicon carbide and magnesium sulphide .
We derive estimates for the inner and outer radius , density and mass of the dust in the shell .
The inner radius is not resolved in our OSCIR imaging , giving an upper limit of 0.4 arcsec .
With this constraint , we conclude that IRAS 19500-1709 must be at least 4 kpc away in order to have the minimum luminosity consistent with a post-AGB status .