We use the progenitor of SN 2012aw to illustrate the consequences of modeling circumstellar dust using Galactic ( interstellar ) extinction laws that ( 1 ) ignore dust emission in the near-IR and beyond ; ( 2 ) average over dust compositions , and ( 3 ) mis-characterize the optical/UV absorption by assuming that scattered photons are lost to the observer .
The primary consequences for the progenitor of SN 2012aw are that both the luminosity and the absorption are significantly over-estimated .
In particular , the stellar luminosity is most likely in the range 10 ^ { 4.8 } < L _ { * } / L _ { \odot } < 10 ^ { 5.0 } and the star was not extremely massive for a Type IIP progenitor , with M _ { * } < 15 M _ { \odot } .
Given the properties of the circumstellar dust and the early X-ray/radio detections of SN 2012aw , the star was probably obscured by an on-going wind with \dot { M } \sim 10 ^ { -5.5 } to 10 ^ { -5.0 } M _ { \odot } /year at the time of the explosion , roughly consistent with the expected mass loss rates for a star of its temperature ( T _ { * } \simeq 3600 _ { -200 } ^ { +300 } K ) and luminosity .
In the spirit of Galactic extinction laws , we supply simple interpolation formulas for circumstellar extinction by dusty graphitic and silicate shells as a function of wavelength ( \lambda \geq 0.3 \mu m ) and total ( absorption plus scattering ) V-band optical depth ( \tau _ { V } \leq 20 ) .
These do not include the contributions of dust emission , but provide a simple , physical alternative to incorrectly using interstellar extinction laws .