THE DUST EXTINCTION, POLARIZATION AND EMISSION IN THE HIGH-LATITUDE CLOUD TOWARD HD-210121

The interstellar extinction, polarization and emission in the high-lat itude cloud toward HD 210121 have been explored in terms of a four-com ponent core-mantle interstellar dust model. We assume that the dust co ntent in this cloud is of Galactic plane origin and has been lifted to its current position either by some sort of (particle) destructive vi olent energetic expulsion (''Galactic fountain''), or by the relativel y gentle ''photolevitation'', or some combination of these two. The po larization curve, peaking at a smaller wavelength than the Galactic av erage, is well fitted by the core-mantle particles with thinner mantle s than for the average interstellar dust as would have resulted from p artial erosion of the Galactic plane core-mantle particles. In modelin g the extinction curve, an extra component of small silicates resultin g from the destruction of the ''laid-bare'' core-mantle particles is a dded to account for the FUV extinction together with PAH's. The sum of the four dust components (core-mantle, hump, PAH's and small silicate s) can be made to closely match the extinction curve which is characte rized by an extremely steep FUV rise. The dust IR emission spectrum ha s also been calculated for radiation fields with various intensity. Co mparison of the model calculation with the IRAS data suggests that the radiation field is weaker than the average interstellar radiation fie ld in the diffuse Galactic interstellar medium. For comparison, attemp ts have also been made to fit the extinction on the basis of the silic ate/graphite (+PAH's) model. While the core-mantle model and the silic ate/graphite+PAH's model are consistent with the solar abundance const raint, the silicate/graphite model needs an unrealistically high silic on depletion to account for the FUV extinction. If the interstellar me dium abundance is only 2/3 of the solar abundance, all models would fa ce the problem of an abundance budget crisis using the standard dust/g as ratio. However, due to the uncertainty of the hydrogen column densi ty, the actual dust/gas ratio may be different from the standard value . Thus the abundance constraint may not be as serious as it appears.