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B. J. Hrivnak (Valparaiso U.), S. Kwok (U. Calgary), T.R. Geballe (Gemini Obs.)
A family of infrared emission features at 3.3, 6.2, 7.7, 8.6, 11.3 \mum are seen in a variety of objects with strong uv radiation fields. These features are attributed to stretching and bending modes of aromatic compounds. An aliphatic feature has been detected at 3.4 \mum in some of these same objects. Proto-planetary nebulae (PPNs) are in a short-lived stage of evolution between the asymptotic giant branch and planetary nebula (PN) phases. It is observed that in this transitional stage, the strengths of some of these infrared emission features differ from those seen in PNs. In particular, the 3.4 \mum feature, which is usually much weaker than the 3.3 \mum feature, is of comparable strength in some PPNs. To better understand the properties of these features, we carried out medium-resolution (R~2000) spectroscopy of a sample of PPNs in the 3 \mum region using the NIRSPEC spectrograph on the Keck II telescope. Eight PPNs were observed. These resulted in the first detection of the 3.4 \mum feature in two objects and possible detections in two others and the first detection of the 3.3 \mum feature in two other objects. We will discuss what has been learned from the observations of the 3.4 \mum feature and review the evidence for a correlation of the ratio of the 3.4 to 3.3 \mum features with spectral type. These observations were carried out in the service observing mode as part of a program of limited access to Keck provided to the Gemini Observatory community. This work was funded in part by grants to BJH from the NSF and to SK by NSERC.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.