The dust extinction , polarization and emission in the high - latitude cloud toward HD 210121

The interstellar extinction, polarization and emission in the high-latitude cloud toward HD 210121 have been explored in terms of a four-component core-mantle interstellar dust model. We assume that the dust content in this cloud is of Galactic plane origin and has been lifted to its current position either by some sort of (particle) destructive violent energetic expulsion (“Galactic fountain”), or by the relatively gentle “photolevitation”, or some combination of these two. The polarization curve, peaking at a smaller wavelength than the Galactic average, is well fitted by the core-mantle particles with thinner mantles than for the average interstellar dust as would have resulted from partial erosion of the Galactic plane core-mantle particles. In modeling the extinction curve, an extra component of small silicates resulting from the destruction of the “laidbare” core-mantle particles is added to account for the FUV extinction together with PAH’s. The sum of the four dust components (core-mantle, hump, PAH’s and small silicates) can be made to closely match the extinction curve which is characterized by an extremely steep FUV rise. The dust IR emission spectrum has also been calculated for radiation fields with various intensity. Comparison of the model calculation with the IRAS data suggests that the radiation field is weaker than the average interstellar radiation field in the diffuse Galactic interstellar medium. For comparison, attempts have also been made to fit the extinction on the basis of the silicate/graphite (+PAH’s) model. While the core-mantle model and the silicate/graphite+PAH’s model are consistent with the solar abundance constraint, the silicate/graphite model needs an unrealistically high silicon depletion to account for the FUV extinction. If the interstellar medium abundance is only 2/3 of the solar abundance, all models would face the problem of an abundance budget crisis using the standard dust/gas ratio. However, due to the uncertainty of the hydrogen column density, the actual dust/gas ratio may be different from the standard value. Thus the abundance constraint may not be as serious as it appears.