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L. Valencic, G. Clayton (Louisiana State University), M. J. Wolff (Space Science Institute), K. Gordon (Steward Observatory), T. L. Smith (Louisiana State University)
In studies of the ISM, it is rare that sightlines are observed over a wide wavelength range, especially the UV and IR regimes. This is due to the fact that the quality of UV data quickly deteriorates in areas of higher extinction, while IR studies focus on spectral features of various materials, from ices, to molecular hydrogen, to polycyclic aromatic hydrocarbons (PAHs). These materials require a dense, protected environment in which to form, which is precisely the environment that UV studies avoid. Because of this separation, dust grain models have tended to depend on the wavelength regime being considered.
In an effort to link these wavelength regimes and thus develop a better-constrained and more complete dust grain model, we have compiled a database of heavily reddened stars from the International Ultraviolet Explorer (IUE) archives and constructed their extinction curves. We recently collected high quality IR spectra (1.9 to 4.1 microns) from the NASA InfraRed Telescope Facility's (IRTF) SpeX instrument for the most heavily reddened sightlines (E(B-V) > 0.80). These spectra will enable us to detect the 3.1 micron ice and 3.4 micron C-H stretch features down to the few percent level. These will help constrain dust grain models by placing limits on how mantling of grains affects UV extinction.