THE STAR-GRAZING EXTRASOLAR COMETS IN THE HD-100546 SYSTEM

Redshifted absorption profiles that resemble the high-velocity circums tellar gas features in the spectrum of beta Pictoris have been detecte d in IUE data for the 10 Myr old Herbig Be star, HD 100546, on 1995 Ma rch 7. In addition to Mg II, Si II, and other refractory species simil ar to those seen in beta Pic, the HD 100546 spectra are rich in accret ing gas profiles from neutral atomic gas, including C I and O I, as we ll as mildly refractory species such as Zn II and S II. The presence o f accreting gas profiles, including neutral atomic gas, is consistent with detection of comae of star-grazing bodies potentially resembling either comets or asteroids. Overall, the IUE data for HD 100546 are co nsistent with the planetesimals in this system being more volatile-ric h and magnesium-rich than similar bodies in the beta Pic system.