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See detailDoubly ionized rare earths in α2 Canum Venaticorum
Swings, Polydore ULg

in Astrophysical Journal (1944), 100

The strongest lines of Eu III, Gd III, Ce III, Sa III, and La III in the region λλ 3070-3300 are identified in the spectrum of α2 CVn. Their intensities and radial velocities undergo changes parallel to ... [more ▼]

The strongest lines of Eu III, Gd III, Ce III, Sa III, and La III in the region λλ 3070-3300 are identified in the spectrum of α2 CVn. Their intensities and radial velocities undergo changes parallel to those of the lines of the corresponding singly ionized elements. Several unidentified lines in the blue-violet region are probably due to Dy III. [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 detailCometary emission spectra in the Visual Region.
Swings, Polydore ULg; McKellar, A.; Minkowski, R.

in Astrophysical Journal (1943), 98

A list of wave lengths of the emission features occurring in the region λ > 4800 has been compiled partly on the basis of previously published data but mainly from measurements of spectrograms of the ... [more ▼]

A list of wave lengths of the emission features occurring in the region λ > 4800 has been compiled partly on the basis of previously published data but mainly from measurements of spectrograms of the recent bright comets 1940c and 1942g obtained at the McDonald, the Mount Wilson, and the Dominion Astrophysical observatories. It is indicated that certain of the more prominent features behave, with respect to the comet's heliocentric distance, as emissions from polyatomic molecules would be expected to do. Comparison of the cometary spectrum with that of an oxyammonia flame leads to the suggested identification of a number of the emission features, among them the strong "λ 6300 group," as due to a dissociation product of ammonia, probably NH2. [less ▲]

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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 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 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 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 detailInvestigations of typical stellar spectra with high dispersion. I. Table of lines in α Cygni.
Struve, Otto; Swings, Polydore ULg

in Astrophysical Journal (1941), 94

This paper contains a new table of wave lengths of absorption lines in the spectrum of α Cygni between λ 3862 and λ 6590.

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See detailThe spectrum of comet Cunningham, 1940C.
Swings, Polydore ULg; Elvey, C.-T.; Babcock, H.-W.

in Astrophysical Journal (1941), 94

Slit spectrograms of Comet Cunningham secured at the McDonald Observatory reveal well-resolved ultraviolet bands due to OH and NH; only the lines of low rotational quantum number are observed, as in the ... [more ▼]

Slit spectrograms of Comet Cunningham secured at the McDonald Observatory reveal well-resolved ultraviolet bands due to OH and NH; only the lines of low rotational quantum number are observed, as in the case of CH. The abundances of OH and NH molecules seem to be of the same order as that of CN. Each branch of the violet bands of CN has two maxima, one corresponding to a rotational distribution for T  400° K and one corresponding to T  50° K. The tail bands of CN are absent. The authors discuss the variation with heliocentric distance of the relative intensities of the vibrational transitions. The rotational intensity distribution and the extension of the different bands in the head have been investigated. The cometary bands of CH belonging to the two electronic transitions, A2∆ → x2∏ (near λ 43oo) and B2∑- → x2∏ (near λ 3900), are described. The bands observed between λ 4000 and λ 4130 are discussed but remain unidentified. [less ▲]

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

in Astrophysical Journal (1941), 94

RX Puppis.-Besides the strong emission lines of H, He I, and He II, this star is characterized by very intense lines of [Fe VII]; other highly ionized elements observed in the spectrum are [Ne V], [Fe VI ... [more ▼]

RX Puppis.-Besides the strong emission lines of H, He I, and He II, this star is characterized by very intense lines of [Fe VII]; other highly ionized elements observed in the spectrum are [Ne V], [Fe VI], and [Ca VII]. The object is very similar to CI Cygni; but the evidence for a late-type component is not as definite. The behavior of the forbidden lines is discussed. Recent variations in the spectra of T Coronae Borealis, Z Andromedae, RW Hydrae, RS Ophiuchi, and AX Persei.-These five objects combine bright lines of high excitation and late-type spectra. In all cases their line-emission spectra observed in the last few years behave in the same way as in novae in their nebular stages; but the ejection velocities are smaller than in single novae, even of the slow type. γ Cassiopeiae.-The observations obtained in 1940 and 1941 were used to determine the contours of the broad lines from the reversing layer. These lines became gradually stronger as the lines produced by the outer shell grew weaker. The optical thickness for continuous radiation of the shell near its maximum development was about τr = 0.2. 14 Comae Berenices.-The spectrum of this star consists of (1) an A5 component of moderate luminosity whose H lines show strong Stark effect and whose lines of Mg II, Si II, Fe II, and Fe I show rapid axial rotation and (2) the spectrum of a shell, which is responsible for sharp Hα but which is otherwise weak in H; the shell also gives rise to sharp lines of Ti II, Cr II, Sc II, Ca II, etc., and resembles the spectrum of Є Aurigae, except that H is much weaker and that the excitation temperature is lower. Some spectroscopic peculiarities of the shell may be accounted for by the hypothesis that the pressure within the shell is lower (perhaps by a factor of 10 or 100) than in normal supergiant reversing layers. [less ▲]

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