Author: Speck A.K. Barlow M.J.
Publisher: Springer Publishing Company
ISSN: 0004-640X
Source: Astrophysics and Space Science, Vol.251, Iss.1-2, 1997-07, pp. : 115-121
Disclaimer: Any content in publications that violate the sovereignty, the constitution or regulations of the PRC is not accepted or approved by CNPIEC.
Abstract
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.
Related content
H2O and HDO bands in the spectra of late-type dwarfs
By Pavlenko Ya.
Astronomy Reports, Vol. 46, Iss. 7, 2002-07 ,pp. :
Discovery and Analysis of Minor Absorption Bands in S-Asteroid Visible Reflectance Spectra
By Hiroi T. Vilas F. Sunshine J.M.
Icarus, Vol. 119, Iss. 1, 1996-01 ,pp. :
Analysis of IUE spectra for the star V1016 Ori
Astronomy Letters, Vol. 27, Iss. 12, 2001-12 ,pp. :