The asymptotic giant branch ( AGB ) star R Sculptoris ( R Scl ) is one of the most extensively studied stars on the AGB .
R Scl is a carbon star with a massive circumstellar shell ( M _ { shell } \sim 7.3 \times 10 ^ { -3 } ~ { } M _ { \odot } ) which is thought to have been produced during a thermal pulse event \sim 2200 years ago .
To study the thermal dust emission associated with its circumstellar material , observations were taken with the Faint Object InfraRed CAMera for the SOFIA Telescope ( FORCAST ) at 19.7 , 25.2 , 31.5 , 34.8 , and 37.1 \mu m. Maps of the infrared emission at these wavelengths were used to study the morphology and temperature structure of the spatially extended dust emission .
Using the radiative transfer code DUSTY and fitting the spatial profile of the emission , we find that a geometrically thin dust shell can not reproduce the observed spatially resolved emission .
Instead , a second dust component in addition to the shell is needed to reproduce the observed emission .
This component , which lies interior to the dust shell , traces the circumstellar envelope of R Scl .
It is best fit by a density profile with n \propto r ^ { \alpha } where \alpha = 0.75 ^ { +0.45 } _ { -0.25 } and dust mass of M _ { d } = 9.0 ^ { +2.3 } _ { -4.1 } \times 10 ^ { -6 } ~ { } M _ { \odot } .
The strong departure from an r ^ { -2 } law indicates that the mass-loss rate of R Scl has not been constant .
This result is consistent with a slow decline in the post-pulse mass-loss which has been inferred from observations of the molecular gas .