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UIR bands in carbon star spectra

Speck, AK; Barlow, MJ; (1997) UIR bands in carbon star spectra. Astrophysics and Space Science , 251 pp. 115-121. 10.1023/A:1000768102477. Green open access

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Unidentified infrared emission bands (UIR bands) have been attributed to polycyclic aromatic hydrocarbons (PAHs), which are believed to require ultraviolet radiation in order for the UIR bands to be excited. If, in addition to amorphous carbon and hydrogenated amorphous carbon (HAC) particles, PAHs are able to form in the outflows of cool carbon-rich stars (Cherchneff et al. 1991), then the weak UV radiation field from such stars would be unlikely to be able to excite the UIR bands and so the PAH species could remain undetected in the spectra of C-stars. However, cool carbon stars with hot companions might be exposed to strong enough UV radiation fields for UIR-band emission to be excited from PAHs. Buss et al. (1991) reported the detection of the 8 µm UIR-band (C-C stretch) in the IRAS LRS spectrum of HD 38218 (TU Tau), a carbon star with a hotter A2III companion. To investigate the phenomenon further, we have therefore obtained UKIRT CGS3 10 µm spectra of three carbon stars with hot companions, TU Tau, UV Aur and CS776. It was found that TU Tau showed the 11.25 µm and 8.6 µm UIR-bands (both attributed to C-H bend modes) at good contrast, while UV Aur clearly exhibited the 11.25 µm UIR band. No narrow UIR-band emission was detected in the spectrum of CS776. We have fitted these 10 µm region spectra using a χ2-minimization program equipped to fit stellar and dust emission continua together with the broad SiC feature and the narrow UIR-bands. The features seen in the spectra of TU Tau and UV Aur can be well fitted by a narrow 11.25 µm UIR-band sitting on top of a broad, self-absorbed 11.3 µm silicon carbide feature. Our results therefore provide strong support for the supposition that PAHs can form in carbon star outflows.

Type: Article
Title: UIR bands in carbon star spectra
Event: International Workshop on Dust and Molecules in Evolved Stars
Dates: 24 March 1997 - 27 March 1997
Open access status: An open access version is available from UCL Discovery
DOI: 10.1023/A:1000768102477
Publisher version: https://doi.org/10.1023/A:1000768102477
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/10113220
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