On Titanium Carbide Nanoparticles as the Origin of the 21 Micron Emission Feature in Post-asymptotic Giant Branch Stars

Li, Aigen

doi:10.1086/381137

Cited by 27 publications

(27 citation statements)

References 18 publications

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“…However, since Ti is a rare element, the abundance test would be a neck to the TiC hypothesis. Indeed, three different groups have already challenged the TiC hypothesis from the Ti abundance point of view (Chigai et al 2003; Hony et al 2003; Li 2003). They all pointed out that there may not be enough titanium to account for the observed strength of this feature.…”

Section: Assessing Individual Carrier Candidatesmentioning

confidence: 99%

On the carriers of the 21 μm emission feature in post-asymptotic giant branch stars

Zhang

Jiang

2009

Monthly Notices of the Royal Astronomical Society

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The mysterious 21 μm emission feature seen in sixteen C‐rich proto‐planetary nebulae (PPNe) remains unidentified since its discovery in 1989. Over a dozen of materials are suggested as the carrier candidates. In this work, we quantitatively investigate eight inorganic and one organic carrier candidates in terms of elemental abundance constraints, while previous studies mostly focus on their spectral profiles (which could be largely affected by grain size, shape and clustering effects). It is found that: (1) five candidates (TiC nanoclusters, fullerenes coordinated with Ti atoms, SiS2, doped‐SiC and SiO2‐coated SiC dust) violate the abundance constraints (i.e. they require too much Ti, S or Si to account for the emission power of the 21 μm band, (2) three candidates (carbon and silicon mixtures, Fe2O3 and Fe3O4), while satisfying the abundance constraints, exhibit secondary features which are not detected in the 21 μm sources and (3) nano FeO, neither exceeding the abundance budget nor producing undetected secondary features, seems to be a viable candidate, supporting the suggestions of Posch, Mutschke & Andersen.

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Section: Assessing Individual Carrier Candidatesmentioning

confidence: 99%

On the carriers of the 21 μm emission feature in post-asymptotic giant branch stars

Zhang

Jiang

2009

Monthly Notices of the Royal Astronomical Society

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“…The origin of these two features is unknown. von Helden et al (2000) identified titanium carbide (TiC) as the carrier of the 21‐μm feature but this has recently been disputed by Li (2003). Speck & Hofmeister (2004) have suggested that SiC may carry the 21‐μm feature.…”

Section: Introductionmentioning

confidence: 99%

Mid-infrared imaging and modelling of the dust shell around post-AGB star HD 187885 (IRAS 19500–1709)

Clube¹,

Gledhill²

2004

Monthly Notices of the Royal Astronomical Society

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We present 10‐ and 20‐μm images of IRAS 19500−1709 taken with the mid‐infrared camera, OSCIR, mounted on the Gemini North Telescope. An extended circumstellar envelope is detected, with the N‐band image indicating an elongation in a north‐east–south‐west direction. We use a dust radiation transport code to fit the spectral energy distribution from ultraviolet to submillimetre wavelengths, with a detached dust shell model. A good fit is achieved using dust composed of amorphous carbon, silicon carbide and magnesium sulphide. We derive estimates for the inner and outer radius, density and mass of the dust in the shell. The inner radius is not resolved in our OSCIR imaging, giving an upper limit of 0.4 arcsec. With this constraint, we conclude that IRAS 19500−1709 must be at least 4 kpc away in order to have the minimum luminosity consistent with a post‐asymptotic giant branch status.

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“…van Helden et al [18] raised Titanium Carbide Clusters (consisting of 27-125 atoms) as the carrier of 21 μm feature. However, Li [19] showed that the abundance of Ti in the 21 μm sources was not enough to account for the observed intensity of the 21 μm band. In 2004, Speck and Hofmeister [20] suggested another candidate, C-doped beta SiC (T = 100 K, radius = 1 μm) and nano SiC grains.…”

Section: Figurementioning

confidence: 99%

The infrared spectral features of circumstellar envelope of evolved low- and intermediate-mass stars

Zhang

Jiang

2008

Sci. China Ser. G-Phys. Mech. Astron.

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The circumstellar envelope of evolved stars of low-and intermediate-mass is animportant site for dust formation. In comparison with the interstellar medium, they have more types of organics and different types of inorganics. Various infrared features in the circumstellar envelope can reveal the composition and abundance of dust, as well as the chemical and physical conditions of the circumstellar shell. Infrared features and their carriers are different in the C-rich or O-rich environment, and the mixed-environment where the C-rich and O-rich circumstellar materials co-exist. The C-rich sources exhibit a series of spectral features which are attributed to organic molecules. They also show two prominent features at 21 μm and 30 μm which emit a large portion of infrared radiation. The O-rich sources exhibit the strong 9.7 μm and 18 μm features attributed to the Si-O bending and O-Si-O stretching modes of amorphous silicate dust. With the ISO/SWS spectrometer, about 50 narrow bands are identified with the crystalline silicate grains, mainly forsterite and enstatite. In addition, a series of features, at 13 μm, 16.8 μm, 19.5 μm and 31.8 μm, appearing to be correlated with each other, are attributed to oxides. Some objects simultaneously show the C-rich and O-rich features, e.g. some C-rich sources have silicate features. There is no well-accepted interpretation for such mixed appearance, though a binary model is suggested.

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On Titanium Carbide Nanoparticles as the Origin of the 21 Micron Emission Feature in Post-asymptotic Giant Branch Stars

Cited by 27 publications

References 18 publications

On the carriers of the 21 μm emission feature in post-asymptotic giant branch stars

On the carriers of the 21 μm emission feature in post-asymptotic giant branch stars

Mid-infrared imaging and modelling of the dust shell around post-AGB star HD 187885 (IRAS 19500–1709)

The infrared spectral features of circumstellar envelope of evolved low- and intermediate-mass stars

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