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

1995, we observed 6 stars from the WW list. Weather conditions were very good,with little or no problems from cirrus. To calibrate the data, we observed knownspectral standards and applied additional corrections to correct for the atmospherictransmission (such as the 10 ym ozone feature). Overall the stability from one nightto the next was excellent. Our general procedure is to observe one grating setting onone night. The setting then is shifted slightly (to fill in gaps caused by bad pixels) andthe observations repeated the second night. This allows us to have two independentspectra that can then be interweaved to provide Nyquist sampling.5. DISCUSSIONWe observed a PsA, P Cas, HD 188037, HD 14432, HD 142666, and 51 Oph. Botha PsA and /3 Cas show no evidence of silicate features but a hint of the onset of athermal dust continuum at 12 Mm. HD 188037 has been reported to have an M starcompanion, which would explain the observed "astronomical" silicate feature we see.HD 144432 has a feature reminiscent of that seen towards GW Ori (a binary youngstellar object thought to have disk). HD 142666 has a broad silicate feature, similarto that that Sylvester et al. (1995) report for HD 98800. Our data show no examplesof PAH-like emission features, though Sylvester et al. report PAH features for threeother sources (HD 169142, HD135344, and HD 141596).51 Oph, thought to be a Be star with a dust disk, was reported by Fajardo-Acostaet al. (1993) to have silicate emission features similar to 0 Pic and comet P/Halley.They found that the dust around 51 Oph was warmer than P Pic and argued thatthe grains would be larger than the grains around 6 Pic. Sylvester et al. (1995) alsoobserved 51 Oph, but make no comment about the emission other than to note it issilicate emission. Our own data has been carefully reduced, and a 550 K blackbodyremoved from the continuum. The feature appears to have an unusual broad shoulderin the emission beyond 10 tcm (Figure 1). One of the glass-rich IDPs discussed byBradley et al. (1992) is similar to the 51 Oph spectra. We applied similar continuumremoval to the HD 142666 and HD 144432 spectra and find prominent bumps in bothspectra at 11 µm. Comparison of the 51 Oph, HD 142666, and HD 144432 spectrawith examples of cometary spectra (Hanner et al. 1993) shows that the P/Halley andP/Bradfield-87 spectra are very simlar. A detailed analysis of the spectral featuresfor each star awaits full models, but it would appear that we can use the comets andIDPs as analogs for the average silicate dust found in some of these systems.The results to date suggest that many of the a Pic-like stars have dust that hasundergone processing similar to that seen in cometary dust.Acknowledgements. HMB wishes to acknowledge the support of the NASAOrigins of the Solar System Program (NAGW-4097) and the Carnegie Institution ofWashington.ReferencesAumann, H. 1985, Pub. A. S. P., 97, 88515