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

Zhang, Ke; Jiang, Biwei; Li, Aigen

doi:10.1111/j.1365-2966.2009.14808.x

Cited by 32 publications

(29 citation statements)

References 46 publications

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“…The 30‐ and 21‐μm features have previously been noted by Hony, Waters & Tielens (2001) and may arise, in the case of the 21‐μm feature, due to large PAH clusters, hydrogenated amorphous carbon grains, hydrogenated fullerenes, nanodiamonds, SiC+SiO 2 grains, TiC nanoclusters and so forth (see e.g. von Helden et al 2000; Zhang, Jiang & Li 2009, and references therein). The range of possibilities appears to be extraordinarily large, although Zhang et al (2009) point to nano‐FeO as the most likely candidate for this emission.…”

Section: The Spectral Properties Of Ngc 40 In the Near‐infrared Andmentioning

confidence: 54%

The halo and rings of the planetary nebula NGC 40 in the mid-infrared

Ramos-Larios¹,

Phillips²,

Cuesta

2010

Monthly Notices of the Royal Astronomical Society

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We present the imaging and spectroscopy of NGC 40 acquired using the Spitzer Space Telescope and the Infrared Space Observatory. These are used to investigate the nature of emission from the central nebular shell, from the nebular halo and from the associated circumnebular rings. It is pointed out that a variety of mechanisms may contribute to the mid‐infrared (MIR) fluxes, and there is evidence for a cool dust continuum, strong ionic transitions and appreciable emission by polycyclic aromatic hydrocarbons (PAHs). Prior observations at shorter wavelengths also indicate the presence of warmer grains and the possible contribution of H2 transitions. Two of these components (warm dust with TGR∼ 500–620 K and PAH emission bands) appear capable, in combination, of explaining the infrared colours of the rings and halo, although the flux ratios are also consistent with shock‐excited H2v= 0–0 emission. It is noted that whilst the surface brightness of the rings is greater in the longer wave (5.8‐ and 8.0‐μm) photometric channels, their fractional fluxes (when compared to the halo) are greater at 3.6 and 4.5 μm, a trend which is similar to those observed in other planetary nebulae. It is also apparent that the relative intensities of the rings are greater than is observed for the Hα+[N ii] transitions. It is suggested that an apparent jet‐like structure to the north‐east of the halo represents one of the many emission spokes that permeate the shell and which are observed for the first time in these MIR results. The spokes are likely to be caused by the percolation of UV photons through a clumpy interior shell, whilst the jet‐like feature is enhanced due to locally elevated electron densities, a result of interaction between NGC 40 and the interstellar medium. It is finally noted that the presence of the PAH, 21‐ and 30‐μm spectral features testifies to appreciable C/O ratios within the main nebular shell. Such a result is consistent with abundance determinations using collisionally excited lines, but not with those determined using optical recombination lines.

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Section: The Spectral Properties Of Ngc 40 In the Near‐infrared Andmentioning

confidence: 54%

The halo and rings of the planetary nebula NGC 40 in the mid-infrared

Ramos-Larios¹,

Phillips²,

Cuesta

2010

Monthly Notices of the Royal Astronomical Society

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“…It likely extends to more bands, such as those comprising the strong and broad 7.7 µm complex, but the effects of band overlap obscure the similarity of the component bands. It is also evident in non-UIR spectra such as the unidentified 21 µm feature (Volk & Kwok 1999;Hrivnak et al 200;Zhang et al 2009). We note that this feature and the NGC 7027 6.2 µm UIR band have nearly identical shapes when overlaid in frequency (i.e., cm -1 ) space.…”

Section: Red Edgementioning

confidence: 97%

A Small Fullerene (C₂₄) may be the Carrier of the 11.2 μm Unidentified Infrared Band

Bernstein

Shroll

Lynch³

et al. 2017

ApJ

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We analyze the 11.2 µm unidentified infrared band (UIR) spectrum from NGC 7027 and identify a small fullerene (C 24 ) as a plausible carrier. The blurring effects of lifetime and vibrational anharmonicity broadening obscure the narrower, intrinsic spectral profiles of the UIR band carriers. We use a spectral deconvolution algorithm to remove the blurring, in order to retrieve the intrinsic profile of the UIR band. The shape of the intrinsic profile, a sharp blue peak and an extended red tail, suggests that the UIR band originates from a molecular vibration-rotation band with a blue band head. The fractional area of the band-head feature indicates a spheroidal molecule, implying a non-polar molecule and precluding rotational emission. Its rotational temperature should be well approximated by that measured for non-polar molecular hydrogen, ~825 K for NGC 7027. Using this temperature, and the inferred spherical symmetry, we perform a spectral fit to the intrinsic profile that results in a rotational constant implying C 24 as the carrier. We show that the spectroscopic parameters derived for NGC 7027 are consistent with the 11.2 µm UIR bands observed for other objects. We present density functional theory (DFT) calculations for the frequencies and infrared intensities of C 24 . The DFT results are used to predict a spectral energy distribution (SED) originating from absorption of a 5 eV photon, and characterized by an effective vibrational temperature of 930 K. The C 24 SED is consistent with the entire UIR spectrum and is the dominant contributor to the 11.2 and 12.7 µm bands.

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“…The origins of the former component are still far from clear, and of the order of ∼10 or so mechanisms have been suggested to explain this excess. Most recently, Zhang, Jiang & Li (2009) have suggested nano‐FeO as the most likely carrier of these bands. The main carrier for the 30 μm feature is also far from clear, although it may correspond to MgS, or some other still unidentified carbonaceous material (see e.g.…”

Section: Colour–colour Diagrams and The Roles Of Differing Emissionmentioning

confidence: 99%

MIPSGAL 24 μm observations of Galactic planetary nebulae

Phillips¹,

Marquez-Lugo²

2010

Monthly Notices of the Royal Astronomical Society

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We have obtained 24 μm imaging, profiles and fluxes for 224 planetary nebulae (PNe) lying within the limits of the Galactic survey undertaken with the Multiband Imaging Photometer for Spitzer (MIPSGAL). It is noted that most of the PNe having extended 24 μm emission also possess circular morphologies, suggesting that the emission derives from cool grains located within the Asymptotic Giant Branch (AGB) mass‐loss regimes. Certain of these haloes are found to have a surface brightness fall‐off which may be consistent with secularly invariant mass loss within the PNe progenitors. By contrast, the 8.0 μm envelopes are detected out to smaller distances from the nuclei, and have a steeper rate of surface brightness fall‐off; a phenomenon which may arise from changes in the excitation of polycyclic aromatic hydrocarbons (PAHs) within external photo‐dissociation regimes (PDRs). Our 24 μm fluxes are compared to those in previously published studies, and this appears to indicate that many of the prior fluxes have been underestimated; a disparity may imply that previous aperture sizes were too small. We have also combined our 24 μm fluxes with measures at shorter mid‐infrared (MIR) wavelengths, taken with the Infrared Array Camera (IRAC). These are used to investigate the positioning of PNe within the IRAC–MIPSGAL colour planes. The [8.0]–[24] and [5.8]–[24] colours are found to be large, and extend over the respective ranges 3.4–8.7 mag, and 5.4–10.3 mag; indices which are only explainable where a broad range of mechanisms contribute to the fluxes, including PAH bands, cool dust continua and a variety of ionic transitions. These and other components also affect the morphologies of the sources, and lead to wavelength‐dependent changes in the widths of the profiles.

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

Cited by 32 publications

References 46 publications

The halo and rings of the planetary nebula NGC 40 in the mid-infrared

The halo and rings of the planetary nebula NGC 40 in the mid-infrared

A Small Fullerene (C₂₄) may be the Carrier of the 11.2 μm Unidentified Infrared Band

MIPSGAL 24 μm observations of Galactic planetary nebulae

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

Cited by 32 publications

References 46 publications

The halo and rings of the planetary nebula NGC 40 in the mid-infrared

The halo and rings of the planetary nebula NGC 40 in the mid-infrared

A Small Fullerene (C24) may be the Carrier of the 11.2 μm Unidentified Infrared Band

MIPSGAL 24 μm observations of Galactic planetary nebulae

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Product

Resources

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A Small Fullerene (C₂₄) may be the Carrier of the 11.2 μm Unidentified Infrared Band