Search for continuous fluorescence in reflection nebulae

Rush, William F.; Witt, A. N.

doi:10.1086/111709

Cited by 8 publications

(6 citation statements)

References 3 publications

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“…LePage et al (2003) suggest that PAHs with fewer than 15-20 atoms are mostly destroyed, those with 20-30 atoms are dehydrogenated, and larger PAHs are largely ionized. The apparent scarcity of small PAHs in the ISM is supported by the absence of any detection of dust luminescence associated with neutral PAHs shortward of 5400 Å in the spectra of reflection nebulae, which are known sources of UIB emission (Donn et al 1989;Rush & Witt 1975). Other studies have suggested dominance by both neutral and ionic species in the ISM (Salama et al 1996;Weingartner & Draine 2001).…”

Section: Discussionmentioning

confidence: 96%

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The Role of Polycyclic Aromatic Hydrocarbons in Ultraviolet Extinction. I. Probing Small Molecular Polycyclic Aromatic Hydrocarbons

Clayton

Salama

Allamandola

et al. 2003

ApJ

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We have obtained new Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra to search for structure in the ultraviolet interstellar extinction curve, with particular emphasis on a search for absorption features produced by polycyclic aromatic hydrocarbons (PAHs). The presence of these molecules in the interstellar medium has been postulated to explain the infrared emission features seen in the 3-13 lm spectra of numerous sources. Ultraviolet (UV) spectra are uniquely capable of identifying specific PAH molecules. We obtained high signal-to-noise ratio UV spectra of stars that are significantly more reddened than those observed in previous studies. These data put limits on the role of small (30-50 carbon atoms) PAHs in UV extinction and call for further observations to probe the role of larger PAHs. PAHs are of importance because of their ubiquity and high abundance inferred from the infrared data, and also because they may link the molecular and dust phases of the interstellar medium. A presence or absence of UV absorption bands due to PAHs could be a definitive test of this hypothesis. We should be able to detect a 20 Å wide feature down to a 3 limit of $0.02 A V . No such absorption features are seen other than the well-known 2175 Å bump.

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Section: Discussionmentioning

confidence: 96%

“…The comparison star spectrum has been scaled by a constant to fit on the plot with the reddened star spectrum. UIB emission (Donn, Allen, & Khanna 1989;Rush & Witt 1975). Other studies have suggested dominance by both neutral and ionic species in the ISM (Salama et al 1996;Weingartner & Draine 2001).…”

Section: Discussionmentioning

confidence: 97%

The Role of Polycyclic Aromatic Hydrocarbons in Ultraviolet Extinction. I. Probing Small Molecular Polycyclic Aromatic Hydrocarbons

Clayton

Salama

Allamandola

et al. 2003

ApJ

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“…The position of the maximum of the band varies from environment to environment and even within a given object from 600 to 850 nm. Efforts dedicated to finding luminescence between 400 and 500 nm resulted in strict upper limits consistent with the absence of photoluminescence in this spectral region (Rush & Witt 1975); (2) The full width at half maximum (FWHM) of the ERE bands changes from 120 to 210 nm. This corresponds to a range from 60 to 120 nm if we consider the width in which half of the total PL energy is concentrated.…”

Section: Ormentioning

confidence: 94%

Crystalline silicon nanoparticles as carriers for the Extended Red Emission

Ledoux

Guillois

Huisken³

et al. 2001

A&A

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Abstract.In an attempt to determine the carrier of the Extended Red Emission (ERE), we have investigated a series of amorphous and crystalline materials: natural coal, amorphous hydrogenated carbon, amorphous hydrogenated silicon carbide, porous silicon, and crystalline silicon nanoparticles. The photoluminescence (PL) behavior of various samples of these materials upon excitation with UV light was studied at room temperature focusing on both the wavelength dependence of the photoluminescence and the PL yield. For some samples the yield is by far too low, other samples do not comply with the characteristic wavelength range of ERE. Only the samples of nanocrystalline silicon (porous silicon and silicon nanoparticles) reveal PL properties that are compatible with the astronomical observations. Besides this experimental evidence, we will supply additional arguments leading to the conclusion that silicon nanoparticles should be seriously considered as an attractive carrier for the Extended Red Emission.

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“…High-efficiency PL occurs in HAC only if the bandgap is large, of order 3 eV , which implies, under UV illumination, blue-green luminescence instead of red emission. The absence of blue emission in astronomical sources (Rush & Witt 1975;Witt & Boroson 1990) argues thus against the presence of such high-bandgap HAC and the large H/C ratios this would imply. Materials such as the HAC sample discussed in this paper can contribute to the ERE in the correct wavelength range, but only with a modest quantum efficiency of about 5%.…”

Section: The Optical Role Of Hac Grains In the Diffuse Ismmentioning

confidence: 99%

The Amount of Interstellar Carbon Locked in Solid Hydrogenated Amorphous Carbon

Furton

Laiho

Witt

1999

ApJ

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Some form of hydrogenated amorphous carbon (HAC) is widely regarded as a likely component of dust in the diffuse interstellar medium of the Galaxy. The most direct observational evidence is the ∼2950 cm −1 C-H stretch feature seen in absorption along heavily attenuated lines of sight. We have used the measured properties of one well-characterized HAC sample, together with well-established correlations between the structural, optical, and infrared (IR) characteristics of HAC materials in general, to estimate the amount of carbon relative to hydrogen that must be bound in this particular solid in interstellar space. The solution to this problem remains uncertain because of the strong dependence of the ∼ 2950 cm −1 mass-absorption coefficient upon the H/C ratio in HAC materials. We estimate that about 80 ppM carbon relative to hydrogen is locked up in interstellar HAC grains with H/C ≃ 0.5. A H/C ratio lower than this value would require higher carbon depletions and result in a ∼ 2950 cm −1 absorption profile inconsistent with observations. Substantially higher H/C ratios, which would imply carbon depletions as low as 20 ppM , would lead to materials exhibiting efficient blue-green photoluminescence, which is not observed. Combined with observations of the gas-phase interstellar abundance of carbon and the revised interstellar reference abundances of refractory elements, this result implies that the bulk of solid carbon in interstellar space is in the form of HAC. In addition to a careful analysis of the IR properties of HAC, we present a summary of the UV/visible optical properties, including the complex index of refraction, measured for one particularly well-characterized HAC sample that is shown to have an IR absorption spectrum which is quantitatively consistent with the latest IR observations of the diffuse interstellar medium.

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Search for continuous fluorescence in reflection nebulae

Cited by 8 publications

References 3 publications

The Role of Polycyclic Aromatic Hydrocarbons in Ultraviolet Extinction. I. Probing Small Molecular Polycyclic Aromatic Hydrocarbons

The Role of Polycyclic Aromatic Hydrocarbons in Ultraviolet Extinction. I. Probing Small Molecular Polycyclic Aromatic Hydrocarbons

Crystalline silicon nanoparticles as carriers for the Extended Red Emission

The Amount of Interstellar Carbon Locked in Solid Hydrogenated Amorphous Carbon

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