C<sub>60</sub><sup>+</sup> diffuse interstellar band correlations and environmental variations

Schlarmann, Leander; Foing, B. H.; Cami, J.; Fan, Haoyu

doi:10.1051/0004-6361/202142669

Cited by 8 publications

(2 citation statements)

References 33 publications

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“…The similarity between each of the four Spitzer PN spectra and laboratory infrared spectra is quantified by the crosscorrelation coefficient, which is a preferred and wellestablished method of choice for the analysis of one component in a complex system (Koenig 1999). For instance, it has been used for detecting chemical species in exoplanet atmospheres (Hoeijmakers et al 2018(Hoeijmakers et al , 2019 or for the study of C 60 + diffuse interstellar band correlations and environment variations (Schlarmann et al 2021). Here, it is [C 60 -Metal] + in the PNe with varying chemical compositions and thermodynamic properties.…”

Section: Discussionmentioning

confidence: 99%

Buckyball-metal Complexes as Potential Carriers of Astronomical Unidentified Infrared Emission Bands

Hou

Lushchikova

Bakker

et al. 2023

ApJ

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Efforts over 40 yr still leave the source of astronomical infrared emission bands largely unidentified. Here, we report the first laboratory infrared (6–25 μm) spectra of gas-phase fullerene-metal complexes, [C60-Metal]+ (Metal = Fe, V) and show with density functional theory calculations that complexes of C60 with cosmically abundant metals, including Li, Na, K, Mg, Ca, Al, V, and Fe, all have similar spectral patterns. Comparison with observational infrared spectra from several fullerene-rich planetary nebulae demonstrates a strong positive linear cross-correlation. The infrared features of [C60-Metal]+ coincide with four bands attributed earlier to neutral C60 bands and in addition also with several bands unexplained to date. Abundance and collision theory estimates indicate that [C60-Metal]+ could plausibly form and survive in astrophysical environments. Hence, [C60-Metal]+ are proposed as promising carriers, in supplement to C60, of observational bands, potentially representing the largest molecular species in space other than C60, C60 +, and C70.

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Section: Discussionmentioning

confidence: 99%

Buckyball-metal Complexes as Potential Carriers of Astronomical Unidentified Infrared Emission Bands

Hou

Lushchikova

Bakker

et al. 2023

ApJ

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“…There is also a small class of so-called C 2 DIBs whose intensity does not correlate with optical extinction (meaning the amount of dust) but with the abundance of C 2 molecules in the gas phase. Recently, C + 60 has been confirmed as a carrier of five DIBs (Campbell et al 2015;Lallement et al 2018;Rouillé et al 2021;Schlarmann et al 2021). Therefore, it is commonly considered that the carriers of DIBs are likely carbonaceous molecules or ions present in the gas phase.…”

Section: Introductionmentioning

confidence: 99%

Electronic spectroscopy of heptacene ions in the search for carriers of diffuse interstellar bands

Meyer

Schiller

Zappa

et al. 2023

A&A

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Context. The absorption bands of the interstellar medium (ISM) in the optical and near-infrared regions called the diffuse interstellar bands (DIBs) have been known for almost a century, yet their origins remain largely unknown. Knowledge of molecular carriers of DIBs would allow for a much better understanding of the chemistry and physics of the ISM. Polycyclic aromatic hydrocarbons (PAHs) and, among them, polyacenes have been suggested as promising candidates for carriers of DIBs. Aims. In this paper, we report on the spectroscopy of heptacene (Hep), the polyacene molecule consisting of seven aromatic rings in a linear arrangement, in its cationic and anionic forms (Hep +/− ). The performed spectroscopic studies made it possible to accurately determine the Hep +/− absorption band positions and to conduct a direct comparison of laboratory and observational spectra. Methods. We utilized helium-tagging action spectroscopy to measure the spectra of Hep +/− in a wide spectral range of 3000 to 13000 Å. In most cases, the spectra obtained by this method can be directly compared with the observational spectra. By analyzing the spectral shift as a function of the number of attached helium atoms, we obtained precise estimates of the gas-phase band positions. Quantum-chemical computations were used to support and interpret the findings. Matrix isolation spectroscopy provided information on the spectral properties of neutral Hep and extended the spectral range for Hep + . Results. We found several absorption bands characterized by a rather large full width at half maximum in the spectra of Hep +/− . The two most intense bands were found at 4714 ± 5 Å and 12250 ± 12 Å for Hep + and at 4673 ± 14 Å and 11326 ± 4 Å for Hep − . We did not find any good match between laboratory and observational spectra. In particular, the intrinsic width of the absorption bands of Hep +/− is much higher than that of most observed DIBs. Conclusions. The non-detection of Hep +/− in the observational spectra excludes the bottom-up formation route for polyacenes in the ISM. Larger polyacene molecules could still be considered as potential carriers of DIBs in the case of an efficient top-down formation route. All currently measured polyacene ions exhibit relatively broad absorption bands. Therefore, additional spectroscopy studies of neutral polyacenes and larger polyacene ions as well as the study of possible top-down formation routes are suggested.

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Diffuse interstellar bands as dust indicators: The contribution from 3D maps

Lallement,

Vergely,

Cox

2024

A&A

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Three-dimensional (3D) distributions of the 862 nm diffuse interstellar band (DIB) carrier have been computed based on Gaia parallaxes and DIB catalogues, in parallel with 3D maps of dust extinction density. Three-dimensional maps provide local diagnostics and information on the distribution of structures in addition to line-of-sight (LOS) integrated quantities, and allow us to focus on poorly studied low-extinction areas. They make cross-matching with other catalogues possible through estimates of the DIB and extinction along any given path. We re-examined the relationships between the density of DIB carriers and the absorption and emission properties of spatially co-located dust. Along with laboratory identifications of carriers, these properties may shed light on the formation and evolution of this organic matter. They may also help to model dust emission and absorption properties in a more detailed way. We used the 3D maps of 862 nm DIBs and of dust extinction, as well as available DIB equivalent width (EW) catalogues and published measurements of parameters characterizing the dust extinction law and the dust emission. We studied the relationships between the extinction-normalized 862 nm DIB EW and the extinction level, the total-to-selective extinction ratio $R_V$, and the dust far-IR emission spectral index beta . We re-visited the link between several DIBs and the UV absorption bump at 220 nm. The ratio of the 862 nm DIB carrier density to the optical extinction density (DIB$_ norm $) is increasing in low-density clouds, confirming with local values the trend seen in the LOS data. In both cases, the coefficients of a fitted power law fall within the range of those measured towards SDSS high-latitude targets for 20 different bands, ranking this DIB among those with a high increase, above that of the broad 4430 DIB. This is consistent with the recent measurement of a larger scale height above the Plane for the 862 nm DIB compared to that of the 4430 DIB. Using map-integrated 862 nm DIB EWs and extinctions along the paths to APOGEE targets with published proxies $R'_V$ for the total-to-selective extinction ratio, we found that, despite a large scatter, DIB$_ norm $ is positively correlated with $R'_V$ for those stars with low to moderate extinctions ($A_V$= 0.2 to 2--3 mag). Independently, using stars from the 862 nm DIB catalogue located outside the disk and for the same regime of extinction, DIB$_ norm $ is found to be globally anti-correlated with the Planck opacity spectral index beta . This is consistent with the observed anti-correlation between beta and $R'_ V $. In the light of a recent result on the variability of the carbon/silicate ratio in dust grains as a source of this anti-correlation, it suggests that DIB$_ norm $ increases with the fraction of carbonaceous to silicate grains in the co-located dust, in agreement with the carbonaceous nature of DIB carriers and recent evidences for a spatial correlation between DIB$_ norm $ and the fluxes of carbon-rich ejecta of asymptotic giant branch (AGB) stars. At higher extinction both trends disappear, and there is evidence for a trend reversal. Regarding the link between the height of the 220 nm UV absorption bump and extinction-normalized EWs of DIBs, we found that two factors explain the absence of previous clear results: the correlation disappears when we move from sigma -type to zeta -type DIBs and/or from single-cloud LOSs to paths crossing multiple clouds distant from each other; zeta -type bands can be used to predict low and high values of the bump height, provided one adds a correcting factor linked to the ambient radiation field (e.g. the 5780/5797 DIB ratio). We show examples of simple models of the bump height based on the 5780 band, the 5850 band and the 5780/5797 DIB ratio. We also found an anti-correlation between DIB$_ norm $ and the width of the bump, which similarly disappears from sigma -type to zeta -type DIBs. This suggests that a fraction of the bump is generated outside the dense molecular clouds. There are complex relationships between DIBs and dust; however, massive measurements of DIBs and extinction and the derived 3D maps may provide some constraints on the density, the nature, and the contribution to extinction and emission of the co-located dust. This requires large stellar spectroscopic surveys and space-based measurements of UV extinction.

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C₆₀⁺ diffuse interstellar band correlations and environmental variations

Cited by 8 publications

References 33 publications

Buckyball-metal Complexes as Potential Carriers of Astronomical Unidentified Infrared Emission Bands

Buckyball-metal Complexes as Potential Carriers of Astronomical Unidentified Infrared Emission Bands

Electronic spectroscopy of heptacene ions in the search for carriers of diffuse interstellar bands

Diffuse interstellar bands as dust indicators: The contribution from 3D maps

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C60+ diffuse interstellar band correlations and environmental variations

Cited by 8 publications

References 33 publications

Buckyball-metal Complexes as Potential Carriers of Astronomical Unidentified Infrared Emission Bands

Buckyball-metal Complexes as Potential Carriers of Astronomical Unidentified Infrared Emission Bands

Electronic spectroscopy of heptacene ions in the search for carriers of diffuse interstellar bands

Diffuse interstellar bands as dust indicators: The contribution from 3D maps

Contact Info

Product

Resources

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C₆₀⁺ diffuse interstellar band correlations and environmental variations