From Stardust to Planetesimals: Contributed Papers - NASA Lunar ...

Detection of Carbon in the 1995 Comet3.0< 2.5CON^ E 2.0Ua^01.51.0X 0.5C 1 (4)01327 1328 1329 1330 1331 1332Wavelength (A)Figure 1. Detection of accreting, atomic carbon as seen in C 1 (4) in the spectrum of HD 100546 on 7March 1995 compared to a quiescent state spectrum from 1993.more quiescent states. The high velocity feature (HVF) is visible in high oscillatorstrength transitions of S II, 0 I, Si II, Si IV, C I, C II, C IV, Al II, Zn II, Mg II, andFe II (see figure 1).2. RESULTS:Size of Gas Cloud: Mg II, the carbon ions, Al II, and the higher oscillator strengthSi II transitions all have saturated absorption profiles with covering factors of 55%,which enables us to infer that the gas cloud had a projected area of 55% of the visiblestellar surface, or for a 3 solar mass star with an estimated radius of 3 Re, a size ofa few times 106 km. This is comparable to the size of the gas clouds seen in Na Itoward the Herbig Ae stars RR Tau, BF Ori, and UX Ori, and is also comparable tothe inferred size of the HVF clouds in the line of sight to Q Pic.Association with Infalling, Evaporating, Bodies: When normalized to quiescentstate spectra of HD 100546, the bulk of the circumstellar gas transitions have absorptionprofiles indistinguishable in shape from those routinely detected toward 0Pic, which have been modelled (Beust et al. 1989; 1995) as the gaseous comae ofinfalling, evaporating bodies. Vidal-Madjar (1994) has noted that additional supportfor an origin of the gas features in the # Pic system from infalling, solid bodies, isprovided by the presence of atomic and or molecular gas features at the system velocityfor elements with first ionization potentials below that of hydrogen (e.g. they can28