Optical spectra of R136

Chu, You‐Hua; Daod, Nazzeha A.

doi:10.1086/131466

Cited by 2 publications

References 3 publications

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Chromogenic Materials, Photochromic

Samat

Guglielmetti

2004

Kirk-Othmer Encyclopedia of Chemical Technology

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Photochromism has been defined as a reversible change in the color, or darkening of a material caused by absorption more generally of ultraviolet or visible light. The change in color is due to a modification of the compound structure and implies a change in the absorption spectrum in the visible range (400–750 nm). The reversion of the system to its original state can be driven either by thermal or photochemical energy (photobleaching), or both, depending on the chemical systems. Photochromic systems are naturally divided into two broad categories : inorganic and organic. Within the inorganic category, the most well‐studied and commercially used systems are those containing silver halide crystallites dispersed throughout a glass matrix. The mechanism of the silver halide photochromism is the reversible formation of silver metal. Both the photochemical formation of silver and the thermal reformation of silver halide are catalyzed by copper ions. The silver halide glass systems have been used commercially in photochromic eyewear. Since 1990, the organic photochromic systems have been a dramatic development in the area of variable optical transmission materials and especially for ophthalmic applications. Indeed polymer glasses have also been greatly developed and are compatible with organic pigments. The most common families are those involving electrocyclic reactions and within this class thermoreversible indolinospirooxazines and naphthopyrans have received the most attention. Indolinospirooxazines were the first photochromic compound used in the preparation of commercially acceptable organic photochromic ophthalmic lenses. Moreover, the area of optical memories and switches has been also a prodigious development and the families of photoreversible fulgides and diaryl (or heteroaryl) ethenes have been extensively studied and used for this type of applications. Finally, many potential applications are possible with photochromic pigments using not only the change of color, but the modifications of physico‐chemical properties under the effect of light irradiation.

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Chromogenic Materials, Photochromic

Samat

Guglielmetti

2004

Kirk-Othmer Encyclopedia of Chemical Technology

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Optical and Ultraviolet Spectral Morphology of Luminous OB Stars in the Galaxy and the Magellanic Clouds

Walborn

1986

Symp. - Int. Astron. Union

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Three areas of current progress relevant to the theme of this Symposium will be discussed. (1) New spectroscopic observations of the 30 Doradus central cluster, obtained independently by the author and by J. Melnick, confirm the presence of numerous very early O-type members, including several of type O3. In combination with sophisticated new direct imagery of the luminous central object R136 by A. Walker and by G. Weigelt, these results have evident implications for understanding the ionization of the supergiant H II region, as well as for the interpretation of R136 itself and of the apparently similar regions seen in more distant galaxies. In particular, no evidence remains for a supermassive object in 30 Doradus, but its central cluster is revealed as a spectacular grouping of very massive hot stars. (2) A further member of the Ofpe/WN9 category in the LMC has been identified, bringing their number to seven, with no exact spectroscopic counterparts yet known in the Galaxy. One of these objects is currently in a state of outburst and has been interpreted by O. Stahl et al. as the hottest known Hubble-Sandage variable. (3) An extensive survey of IUE high-resolution data has revealed a strong correlation between the ultraviolet stellar wind features and the optical spectral classifications for the majority of normal O stars. These results are relevant to future studies with the High Resolution Spectrograph on the Hubble Space Telescope, which may observe restricted UV wavelength ranges in faint extragalactic OB stars lacking optical data of comparable quality.

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Optical spectra of R136

Cited by 2 publications

References 3 publications

Chromogenic Materials, Photochromic

Chromogenic Materials, Photochromic

Optical and Ultraviolet Spectral Morphology of Luminous OB Stars in the Galaxy and the Magellanic Clouds

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