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See detailSpectrographic observations of Nova Herculis (1934) and Nova Serpentis (1909), with identifications of [Fe v] and [Fe III] in Nova Pictoris (1925).
Swings, Polydore ULg; Struve, Otto

in Astrophysical Journal (1942), 96

I. The velocities of expansion of Nova Herculis show a range of from 338 km/sec for [O II] to 256 km/sec for [O III]. This suggests stratification. The lines show curved outer components, with a faint ... [more ▼]

I. The velocities of expansion of Nova Herculis show a range of from 338 km/sec for [O II] to 256 km/sec for [O III]. This suggests stratification. The lines show curved outer components, with a faint indication of a central line in the case of Hγ. Considerable change has taken place in the relative intensities of the emission lines since 1940. The continuous spectrum of the central star has decreased in brightness. II. The forbidden spectra of [Fe V] and [Fe VI] are well developed in the present spectrum of Nova Serpentis. Although thirty-three years have elapsed since the outburst, the electron density in the nebulosity is still high, compared with most planetary nebulae. III. Several unidentified lines measured by H. Spencer Jones in Nova Pictoris (1925) can now be attributed to [Fe V] and [Fe III]. [less ▲]

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See detailConsiderations regarding cometary and interstellar molecules.
Swings, Polydore ULg

in Astrophysical Journal (1942), 95

The visual continua in the spectra of three nebulae photographed with a narrow slit are not produced by the blending of atomic emission lines but must have a physical origin. Several strong He I emission ... [more ▼]

The visual continua in the spectra of three nebulae photographed with a narrow slit are not produced by the blending of atomic emission lines but must have a physical origin. Several strong He I emission lines just beyond the Balmer limit may tend to vitiate measurements of the intensity distribution in the Balmer continuum on plates taken with a wide slit. [less ▲]

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See detailThe interpretation of the spectrum of HD 190073.
Struve, Otto; Swings, Polydore ULg

in Astrophysical Journal (1942), 96

The hypothesis proposed by Beals for the interpretation of the complex contours of lines of H and Ca II in HD 190073 is discussed in the light of recent observations made at the McDonald Observatory. The ... [more ▼]

The hypothesis proposed by Beals for the interpretation of the complex contours of lines of H and Ca II in HD 190073 is discussed in the light of recent observations made at the McDonald Observatory. The absorption lines designated by Beals as A2 and A3 and the emission of Ca II and H probably originate in a shell whose radius is several times larger than the radius of the star. The absence of A1 near the center of the emission in Ca II H suggests that this sharp line is produced at a lower level, where the velocity of expansion is negligible. The central reversals of the H lines, on the other hand, may come from an upper layer of the shell where the atoms have become decelerated. In this case the absorbing layer must lie immediately above an optically thick emitting shell, so that it will act somewhat like a reversing layer and not like a detached shell at great distances from the emitting regions. [less ▲]

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See detailContinuous Emission in the Spectra of Gaseous Nebulae.
Swings, Polydore ULg; Struve, Otto

in Astrophysical Journal (1942), 96

The visual continua in the spectra of three nebulae photographed with a narrow slit are not produced by the blending of atomic emission lines but must have a physical origin. Several strong He I emission ... [more ▼]

The visual continua in the spectra of three nebulae photographed with a narrow slit are not produced by the blending of atomic emission lines but must have a physical origin. Several strong He I emission lines just beyond the Balmer limit may tend to vitiate measurements of the intensity distribution in the Balmer continuum on plates taken with a wide slit. [less ▲]

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See detailSpectrographic observations of peculiar stars. III.
Swings, Polydore ULg; Struve, Otto

in Astrophysical Journal (1942), 95

This paper describes recent changes in the spectra of AX Per, Z And, AG Peg, and R Aqr. There is also a description of recent spectrograms of the unusually red bright-line star MWC 349.

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See detailTerm analysis of the third spectrum of iron (Fe III).
Edlèn, B.; Swings, Polydore ULg

in Astrophysical Journal (1942), 95

The Fe III spectrum has been measured in the region from approximately 500 A to 6500 A, and its analysis has been carried as far as the observational data permit. Of the 34 theoretically possible terms of ... [more ▼]

The Fe III spectrum has been measured in the region from approximately 500 A to 6500 A, and its analysis has been carried as far as the observational data permit. Of the 34 theoretically possible terms of the 3d6 configuration, 32 have been found, the 2 high 1S and 1D terms being the only missing ones. Of the 74 theoretical levels for 3d5 4s, only 10 high-lying levels1, 3(SPD) have not been found. Of the configuration 3d5 4p, practically all theoretically possible levels corresponding to those found of 3d5 4s have been established. The final tables contain 320 levels and approximately 1500 classified lines. The permitted and forbidden transitions of Fe III play an important role in a wide variety of stellar and nebular spectra. [less ▲]

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See detailSpectrographic Observations of Peculiar Stars.IV.
Swings, Polydore ULg; Struve, Otto

in Astrophysical Journal (1942), 96

I. New observational results.-AX Persei in January and February, 1942, showed the lines of [Fe V] and [Fe VI] with considerable intensity. Other interesting changes in the spectrum have been recorded. RW ... [more ▼]

I. New observational results.-AX Persei in January and February, 1942, showed the lines of [Fe V] and [Fe VI] with considerable intensity. Other interesting changes in the spectrum have been recorded. RW Hydrae is interesting because of the absence of fluorescence excitation in O III and because the He I singlets (2p1P0 - nd1D) are relatively strong. Z Andromedae has returned to a stage similar to that observed in August, 1940. T Coronae Borealis has bright Fe II, but the absence of [Ne V] shows that the excitation is lower than in Z Andromedae. Z Canis Majoris has been observed near maximum light. Several Of and W stars have also been observed. II. Excitation mechanisms in shells.-The importance of fluorescence excitation is discussed and is applied to the problem of selectivities among emission lines of peculiar stars. Of particular interest are the ratios of singlet to triplet intensities of He I. The great relative strength of the singlets in objects of low excitation, like RW Hydrae, is attributed (a) to the predominance of fluorescence over recombination and (b) to the presence of high radiation density in the nebulous shells of the singlet series (1s1S - np1P0) of He I. Similar considerations are applied to unusual intensities of emission lines in Of shells and in P Cygni or Be shells. The influence of departures of the exciting radiation from that of a black body is discussed for novae and for certain long-period variables. When fluorescence is produced by strong ultraviolet emission lines, as in the case of Bowen's mechanism for O III, the gradient in the velocity of expansion of a shell produces important modifications. This may account for absence of the Bowen mechanism in Wolf-Rayet stars and in other rapidly expanding shells. [less ▲]

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See detailThe problems of the A-type stars
Struve, Otto; Swings, Polydore ULg

in Observatory (The) (1942), 64

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See detailThe spectrum of Comet 1942a (Whipple).
Popper, D.-M.; Swings, Polydore ULg

in Astrophysical Journal (1942), 96

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See detailThe spectra of Wolf-Rayet Stars and related objects.
Swings, Polydore ULg

in Astrophysical Journal (1942), 95

New observational data are given for the spectra of several Wolf-Rayet stars. Evidence is produced for the presence of C IV in the WN sequence and for a central reversal of the H, He I, and He II lines ... [more ▼]

New observational data are given for the spectra of several Wolf-Rayet stars. Evidence is produced for the presence of C IV in the WN sequence and for a central reversal of the H, He I, and He II lines. The spectra of two Of stars are described, and some properties of the Of shells are discussed, especially the ionization conditions and the excitation process. The absence of well-marked dilution effects and other considerations suggest that the size of a Wolf-Rayet shell is not much larger than that of the photospheric surface, so that an occultation effect should be expected in certain cases. The relative abundances of carbon and nitrogen in the ejected shells of Wolf-Rayet, Of, and P Cygni stars, as well as of novae, are discussed, since W objects have been observed which are intermediate between the pure nitrogen and carbon sequences. Suggestions are made concerning the classification, absolute magnitudes, temperatures, and radii of Wolf-Rayet stars and planetary nuclei, as well as concerning the application of Zanstra's theory to the nebulae with a Wolf-Rayet nucleus or to the Wolf-Rayet stars themselves. [less ▲]

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See detailMolecular bands in cometary spectra. Identifications
Swings, Polydore ULg

in Reviews of Modern Physics (1942), 14

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See detailNote: Remarks on the Spectra of Comets 1941c (Paraskevopoulos-De Kock) and 1941d (van Gent).
Elvey, C. T.; Swings, Polydore ULg; Babcock, H. W.

in Astrophysical Journal (1942), 95

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See detailThe Spectrum of a2 Canum Venaticorum.
Struve, Otto; Swings, Polydore ULg

in Astrophysical Journal (1942), 98

A new list of wave lengths containing 3107 absorption lines between λ 3087.9 and λ 4740.6 has been obtained from 28 spectrograms taken at the Mount Wilson and the McDonald observatories. Of these plates ... [more ▼]

A new list of wave lengths containing 3107 absorption lines between λ 3087.9 and λ 4740.6 has been obtained from 28 spectrograms taken at the Mount Wilson and the McDonald observatories. Of these plates, 18 were obtained with a dispersion of around 3 A/mm, while the other plates, used in the ultraviolet region, had 20 A/mm. The identifications are based upon all available laboratory material and show that all singly ionized rare earths which have been measured in the laboratory and which have a sufficient number of fines in the region covered by the stellar spectrograms are present. One doubly ionized rare earth, Ce III, is almost certainly present, and others may contribute to blends. The intensities of all rare-earth lines are variable in a period of 5.5 days and follow the pattern of the Eu II lines (designated as group A). The lines of Cr II and some other elements vary in the opposite sense (group B), while certain other lines—Si II, Mg II, etc.—do not appreciably change in intensity (group C). The radial velocities as measured from the lines of different elements also fall into three groups, designated as a, b, and c, which roughly correspond to the intensity groups A, B, and C. Group a, consisting of the rare earths and some other elements predominantly of low ionization potential, shows a shallow minimum of velocity at phase 4.5 days after maximum Eu II intensity and a sharp maximum of velocity at phase 1.5 days. Group b, represented by Cr II and some other elements, shows a velocity-curve with a double wave. The highest maximum is at phase 5.0 days and the deepest minimum at phase 0.7 day. Group c, consisting of Mg II, Si II, H, and Ca II, shows no appreciable variation. [less ▲]

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See detailSpectra of comets
Swings, Polydore ULg

in Publications of the Astronomical Society of the Pacific [=PASP] (1942), 54

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See detailMolecules: their role in astronomy
Swings, Polydore ULg

in Publications of the Astronomical Society of the Pacific [=PASP] (1942), 54

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