[en] High signal-to-noise ratio 5-8 μm spectra of four sources embedded in molecular clouds are presented. All four sources show evidence for the presence of absorption features. The shape of these features changes, however, dramatically from source to source. They range from two relatively narrow bands at 6.0 and 6.8 μm in W33A to a broad, shallow feature, which extends from about 5.2 to 7.8 μm and shows some structure, in Mon R2-IRS2, BN, and NGC 2264

[en] A classification scheme for QSO absorption line spectra is described which ascribes the origin of the lines to at least four mechanisms: (A) Explosive ejection of material at speeds up to 0.1 c. (B) Absorption by highly ionized material moving in a rich cluster in which the QSO is embedded. (C-1) Cosmologically distant intervening material with 'normal' abundances, probably associated with large galactic halos. (C-2) Cosmologically distant intervening material consisting of primordial uncondensed gas. Examples of each type of spectra are given and their ionization and other spectral characteristics discussed. The similarity between the development of novae spectra and a possible evolutionary sequence of the explosive ejecta of type A is striking and suggestive. Several difficulties and unsolved problems involving this scheme are noted. Finally, the author speculates on the interpretation of two interesting objects (PKS 0237-23 and the 'twin quasars' 0957+56A,B) in the context of this scheme. (Auth.)

No abstract available

No abstract available

[en] The optical spectra of PbMoO₄:Er³+ single crystals at 77 and 300K are investigated, the optical transitions of Er³+ ions in the crystals are identified and the experimental scheme of Stark splitting of Er³+ ions lowest multiplets are obtained. 6 refs

[en] In a combined theoretical and experimental work, we investigate X-ray absorption near-edge structure spectroscopy of the I L₃ and the Pb M₅ edges of the methylammonium lead iodide (MAPbI₃) hybrid inorganic-organic perovskite and its binary phase PbI₂. The absorption onsets are dominated by bound excitons with sizable binding energies of a few hundred millielectronvolts and pronounced anisotropy. The spectra of both materials exhibit remarkable similarities, suggesting that the fingerprints of core excitations in MAPbI₃ are essentially given by its inorganic component, with negligible influence from the organic groups. Furthermore, the theoretical analysis complementing experimental observations provides the conceptual insights required for a full characterization of this complex material.

No abstract available

No abstract available

[en] The A and B bands of calcium hydride are identified at high dispersion in the SC star, UY Cen. In the SC stars, the B band is largely responsible for the lambda 6379 absorption noted by Rybski (1973). CaH is also present in the CS star TT Cen, but may not be responsible for the lambda 6379 absorption in WZ Cas. (U.S.)

[en] The reliability of identifications of narrow absorption lines with small red shifts is analyzed statistically on the basis of literature data on spectra with high spectral resolution for 38 quasi-stellar objects. The identifications were made using a reference spectrum including the most pronounced lines of the interstellar medium. Particular attention is devoted to the case of quasi-stellar objects in the region + or - 10 deg from the supergalactic equator or coincident in position on the celestial sphere with high-latitude high-velocity hydrogen clouds, and also situated at small angular distances from nearby galaxies. It is shown that in the majority of cases identifications with the line pairs of Ca II and Na I are random