VARIABLE EXTINCTION IN HD-45677 AND THE EVOLUTION OF DUST GRAINS IN PRE-MAIN-SEQUENCE DISKS

Changes in the UV extinction and IR emission were sought in the Herbig Ae/Be star candidate HD 45677 (= FS CMa) by comparing UV, optical, an d IR observations made approximately 10 yr apart. HD 45677 varied sign ificantly, becoming more than 50% brighter in the UV and optical than it was a decade ago. A comparison of the observations between epochs i ndicates that if the variations are due to changes in dust obscuration , the dust acts as a gray absorber into the near-IR and must be deplet ed in grains smaller than 1 mu m. This is similar to the results obtai ned on the circumstellar disks of stars like Vega and beta Pic, and su ggests that radiation pressure may be responsible for the small-grain depletion. In addition, the total IR flux seems to have declined, indi cating a decrease in the total mass of the dust envelope that contribu tes to the IR emission in this part of the spectrum. Due to the anomal ous nature of the extinction, the use of normal extinction curves to d eredden the spectral energy distributions of stars with circumstellar dust may lead to significant errors and should be used with great caut ion.