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تسجيل مستخدم جديدDiffuse bands 9577 and 9633 -- relations to other interstellar features
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We study, for the first time, the relations of two strong diffuse bands (DIBs) at 9633 and 9577~AA, commonly attributed to C$_{60}^+$, to other interstellar features seen in optical and UV spectra including H{sc i}, Ca{sc i}, Fe{sc ii}, Na{sc i}, Ti{sc ii}, CN, CH, CH$^+$, and C$_2$ and DIBs 5780, 5797, 6196, 6269, 6284, and 6614. We analyzed 62 lines of sight where the stellar contamination by Mg{sc ii} was corrected or found negligible for DIB 9633. Equivalent widths of DIB 9577 were measured in 62 lines of sight. Poor mutual correlation between the strengths of the above features and the major diffuse bands (5780 and 5797) as well as with other DIBs (with some exceptions) were revealed. The considered DIBs are also poorly correlated with the features of neutral hydrogen, molecular carbon, and those of simple interstellar radicals. Perhaps this phenomenon can be explained if the diffuse band 9577 is an unresolved blend of two or more interstellar features. There are indications that 9633 and 9577 diffuse bands are stronger in $sigma$-type clouds, i.e. these features resemble the behavior of reasonably broad DIBs, which are strong in the lines of sight where the UV flux from the very hot nearby stars plays an important role.
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The identification of the carriers of the diffuse interstellar bands (DIBs) remains to be established, with the exception of five bands attributed to C60+, although it is generally agreed that DIB carriers should be large carbon-based molecules (with
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ellar fullerenes of various sizes with endohedral or exohedral inclusions and heterofullerenes (EEHFs). The phenomenology of fullerenes is complex. In addition to fullerene formation in shock shattering, fully dehydrogenated PAHs in diffuse interstellar (IS) clouds could perhaps efficiently transform into fullerenes including EEHFs. But it is extremely difficult to assess their expected abundance, composition and size distribution, except for C60+. EEHFs share many properties with C60, as regards stability, formation/destruction and chemical processes, and many basic spectral features. We address the interstellar importance of various EEHFs as possible DIB carriers. Specifically, we discuss IS properties and the contributions of fullerenes of various sizes and charge such as C60+, metallofullerenes, heterofullerenes, fulleranes, fullerene-PAH compounds, H2@C60. We conclude that the landscape of interstellar fullerenes is probably much richer than heretofore realized. EEHFs, together with pure fullerenes of various sizes, have properties necessary to be suitably carriers of DIBs: carbonaceous nature; stability and resilience in the ISM; various heteroatoms and ionization states; relatively easy formation; few stable isomers; right spectral range; energy internal conversion; Jahn-Teller fine structure. This is supported by the C60+ DIBs. But, the lack of information about optical spectra other than C60 and IS abundances still precludes definitive assessment of the importance of fullerenes as DIB carriers. Their compounds could significantly contribute to DIBs, but it still seems difficult that they are the only important DIB carriers.
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