Pah Formation: 3.3 And 11.3 μm Data
The unidentified infrared bands (UIBs) have been attributed to emission from polycyclic aromatic hydrocarbons (PAHs). The UIBs at 3.3 and 11.3 micron, among others, are seen in many astrophysical environments, with the notable exception of carbon-rich AGB stars (C stars). PAHs are expected to form around C stars, yet only a few show the UIBs and all of these have hot companions. This makes C stars with hot companions an ideal environment to study the conditions associated with PAH formation and processingThe precise wavelengths and ratios of the features depend on the size, composition, and charge state of the individual PAHs. Additionally, the wavelength of photons needed to excite PAHs depends on the individual PAHs size and charge state. While small PAHs undoubtedly need higher energy (UV) photons, it has been suggested that large (>100 C atoms) or ionized PAHS can be excited by visible or even near-IR photons. The lack of PAH emission from single carbon stars suggests that either PAHs do not form around C stars, or that only small neutral grains form which cannot be excited by a C star's soft radiation field. We present new observations of several C stars with hot companions in order to understand the distribution of PAHs responsible for the emerging UIB emission. Observations taken using NIRI/Altair on Gemini North provide the spatial distribution of the 3.3 micron UIB emission, while observations taken using Michelle on Gemini North provide the spatial distribution of the 11.3 micron UIB emission. By comparing the distributions of these emission bands, we build a coherent picture of the size and charge state of PAHs around these carbon stars, and how that varies by location. This will provide the basis for understanding the formation and processing of PAHs.
American Astronomical Society Meeting Abstracts #214
- Pub Date:
- May 2009