References of "Struve, Otto"
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See detailThe Evolution of a Peculiar Stellar Spectrum: Z Andromedae
Swings, Polydore ULg; Struve, Otto

in Herbig, G. H. (Ed.) Spectroscopic Astrophysics: An Assessment of the Contributions of Otto Struve (1970)

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See detailThe problem of the rare earths in α2 Canum Venaticorum
Struve, Otto; Swings, Polydore ULg

in Publications of the American Astronomical Society (1946), 10

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

in Astrophysical Journal (1945), 101

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See detailThe spectrum of Comet Whipple 2 (1942f)
Swings, Polydore ULg; Struve, Otto

in Publications of the Astronomical Society of the Pacific [=PASP] (1943), 55

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See detailThe spectrum of PLEIONE.
Struve, Otto; Swings, Polydore ULg

in Astrophysical Journal (1943), 97

The radial velocity of Pleione shows oscillations with a range of 10 km/sec and a period of about four months. The mean velocity is +5.5 km/sec. The spectrum of the shell, first discovered by McLaughlin ... [more ▼]

The radial velocity of Pleione shows oscillations with a range of 10 km/sec and a period of about four months. The mean velocity is +5.5 km/sec. The spectrum of the shell, first discovered by McLaughlin and Mohler in 1938, has gradually become stronger and now resembles the metallic spectrum of α Cygni. Dilution effects are conspicuous in the weakness of Mg II and Si II. Among the lines of ions having metastable lower levels, Ni II and Fe II became conspicuous in 1940, Ti II in 1941, and Mn II in 1942. This order of development is not consistent with the ordinary theory of ionization, and its explanation must be sought in the conditions of excitation of the metastable levels in the shell. The central intensities of the cores of the H lines are about 10 per cent—roughly one-half or one-third of the central intensities of the corresponding lines in α Cygni. This is explained as a consequence of the reduced re-emission which is thrown back within the shell into the emerging beam of radiation from the star. The metallic lines on the violet side of the Balmer limit and between the higher members of the series are relatively much stronger than in α Cygni. This is due to the semitransparency of the shell, on the one hand, and to the absence of Stark effect wings in the shell, on the other. [less ▲]

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

in Astrophysical Journal (1943), 98

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

in Observatory (The) (1942), 64

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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 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 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 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 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 detailOn the emission lines in the spectrum of BD +20° 2465
Swings, Polydore ULg; Struve, Otto

in Publications of the Astronomical Society of the Pacific [=PASP] (1941), 53

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See detailThe spectrum of Nova Monocerotis, 1939
Swings, Polydore ULg; Struve, Otto

in Publications of the Astronomical Society of the Pacific [=PASP] (1941), 53

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See detailVariations in the spectrum of HD 108
Swings, Polydore ULg; Struve, Otto

in Publications of the Astronomical Society of the Pacific [=PASP] (1941), 53

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See detailA contribution to the study of β Canis Majoris.
Struve, Otto; Swings, Polydore ULg

in Astrophysical Journal (1941), 94

Coudé spectrograms obtained at the McDonald Observatory on January 22 and 24, 1941, show a velocity range of about 9 km/sec, in a period of 6 hours. The lines are diffuse and shallow near minimum velocity ... [more ▼]

Coudé spectrograms obtained at the McDonald Observatory on January 22 and 24, 1941, show a velocity range of about 9 km/sec, in a period of 6 hours. The lines are diffuse and shallow near minimum velocity and sharper and deeper near maximum velocity. The Ca II line K shares in the oscillations. It is probably a blend of a stellar and an interstellar line. The lines suggest turbulence of an appreciable amount. A line at λ 4469.71 is probably a blend of O II and forbidden He I. A comparison with β Cephei shows that β Canis Majoris is more luminous. It is, however, not a supergiant. The similarity in the periods suggests similarity of internal structure. [less ▲]

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See detailTwo interesting nuclei of planetary nebulae: IC 418 and NGC 40
Swings, Polydore ULg; Struve, Otto

in Proceedings of the National Academy of Sciences of the United States of America (1941), 27

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See detailThe emission lines in the spectra of B 1985 and WY Geminorum.
Swings, Polydore ULg; Struve, Otto

in Astrophysical Journal (1941), 93

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See detailThe spectrum of the Shell of PLEIONE.
Struve, Otto; Swings, Polydore ULg

in Astrophysical Journal (1941), 93

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