Modeling anomalous extinction using nanodiamonds

Modeling extinction along anomalous/non-CCM sightlines, which are characterized by a broad $217.5 nm$ bump and steep far-ultraviolet (FUV) rise, is reported. The extinction along these sightlines, viz. {HD 210121}, {HD 204827}, {HD 29647} and {HD 62542}, is difficult to reproduce using standard silicate and graphite grains. Very good match with the observed extinction is obtained by considering nanodiamond component as part of carbonaceous matter. Most of these sightlines are rich in carbon and are invariably backed by a young hot stellar object. Nanodiamond is taken as core within amorphous carbon and graphite. These core-mantle particles taken as additional components along with graphite and silicates lead to reduction in the silicate requirement. The abundance of carbonaceous matter is not affected as a very small fraction of nanodiamond is required. Extinction along sightlines that show steep FUV is also reported demonstrating the importance of nanodiamond component in all such regions.