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See detailThe relative intensities of the coronal and other forbidden lines.
Bowen, I.-S.; Swings, Polydore ULg

in Contributions from the Mount Wilson Observatory (1947), 725

The behavior of the coronal lines in RS Ophiuchi, T Pyxidis, and T Coronae Borealis is in accord with the physical properties of these lines as predicted from Edlén's identifications. Observed anomalies ... [more ▼]

The behavior of the coronal lines in RS Ophiuchi, T Pyxidis, and T Coronae Borealis is in accord with the physical properties of these lines as predicted from Edlén's identifications. Observed anomalies in the relative abundance of certain ions in these and similar objects may be explained by irregularities in the intensity-curve of the primary exciting radiation of the central star, caused by H and He II continuous absorption. One line in the RS Oph spectrum is identified with [K XI]. [less ▲]

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See detailIdentification of the post-maximun lines in the spectrum of nova (RS) Ophiuchi.
Joy, A.-H.; Swings, Polydore ULg

in Contributions from the Mount Wilson Observatory (1945), 714

Interest in the spectra of recurring novae has been aroused by the recent (fourth) outburst of Nova (T) Pyxidis. A review of the hitherto unpublished measures of the Mount Wilson spectrograms of Nova (RS ... [more ▼]

Interest in the spectra of recurring novae has been aroused by the recent (fourth) outburst of Nova (T) Pyxidis. A review of the hitherto unpublished measures of the Mount Wilson spectrograms of Nova (RS) Ophiuchi obtained between September 2 and November 10, 1933, shows many plausible identifications of lines which were impossible earlier. The atoms now identified, in addition to H, are: He I, He II, C III, [N II], N III, [O I], O III, [O III], [Ne III], [Ne IV], Na I, Si I, Si II, Si III, Si IV, [S II], [S III], [A V], [A X], [A XI], [K IV], [K V], [Ca V], [Ca VI], [Ca VII], [Ca XIII], [Sc VII], [V VIII], Fe II, [Fe II], [Fe IV], [Fe V], [Fe VI], [Fe VII], [Fe X], [Fe XI], [Fe XIV], [Ni XII], [Zr III]. Of these, [A XI] λ 6919, [Ca VII] λ 3688 (and possibly [V VIII] λ 3686), [Sc VII] λ 4823, and [Kr III] λ 6827 are identified for the first time. Considerations of the physical conditions in the solar corona as compared with those in the recurrent novae indicate marked differences, the coronal strata not permitting radiation of forbidden lines in the lower stages of ionization such as are found in the novae. [less ▲]

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See detailA strong infrared radiation from molecular nitrogen in the night sky.
Stebbins, Joel; Whitford, A.-E.; Swings, Polydore ULg

in Contributions from the Mount Wilson Observatory (1945), 703

A new infrared radiation has been detected in the night sky, which is far more intense than the ordinary persistent aurora giving the green line at 5577 A. Measured with a photocell and filters, the wave ... [more ▼]

A new infrared radiation has been detected in the night sky, which is far more intense than the ordinary persistent aurora giving the green line at 5577 A. Measured with a photocell and filters, the wave length of the new radiation is 10,440 ± 25 A. This night-sky radiation is identified with the (0, 0) band of the first positive group B3∏ → A3Σ of N2. The absence of other N2 bands suggests that emission of the (0, 0) band involves conversion of the energy of dissociation D(N2) into excitation in a three-body collision: N + N + N2 → N2 + N2exc . Since D(N2) is a little larger than the excitation energy of B3∏, ν' ≈ 0, but smaller than B3∏, υ' = 1, only the bands arising from B3∏, υ' = 0, would be excited; and of the latter, only (0, 0) is observable. This mechanism implies the presence of a large number of nitrogen atoms in the high atmosphere. It can be effective only with the value 7.38v. of D(N2) advocated by Herzberg and Sponer. [less ▲]

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See detailComparative study of the red and violet systems of cyanogen bands.
King, Arthur-S.; Swings, Polydore ULg

in Contributions from the Mount Wilson Observatory (1945), 700

Comparison of bands belonging to the violet and red systems of CN showed that in emission the (1, 0) band λ 7873 (red system) is stronger than the (0, 0) band λ 3883 (violet system) at temperatures of the ... [more ▼]

Comparison of bands belonging to the violet and red systems of CN showed that in emission the (1, 0) band λ 7873 (red system) is stronger than the (0, 0) band λ 3883 (violet system) at temperatures of the electric furnace below 2300° C. Approximate equality of the main structure of the two bands is attained at 2300° C; λ 3883 becomes somewhat stronger than λ 7873 at 2600° C. At the high temperature, approximately 7300° C, of the carbon arc in air, the λ 3883 band is about two hundred times stronger than the λ 7873 band. Self-reversal appears easily in the violet band, but not in the red. The two systems react differently to a change in pressure, the red system increasing in intensity more rapidly than the violet when the pressure increases. In absorption, the (0, 0) and (1, 0) bands of the red system are much weaker than the violet bands at any temperature of the furnace. A list of the stronger absorption lines of the λ 7873 band is given. The relative intensities of the two systems in emission in the electric furnace at different temperatures and in the arc are explained by the Boltzmann populations of the upper levels in thermodynamic equilibrium. These populations differ strongly because the upper electronic level, A2Π, of the red system is much lower (e.p., 1.35 v.) than the upper level, B2∑, of the violet system (3.2 v.). From the equal intensity of the strongest lines of the two systems in emission at T = 2300° C, an approximate value of 1400 is found for the ratio of the emission transition probabilities of the strongest violet lines to those of the strongest red lines. The corresponding estimated value of the ratio of the absorption transition probabilities is 87.5, explaining the weakness of the red system in absorption in the laboratory. These considerations show that the red bands of CN should not be expected in fluorescence in comets and that previous identifications must be revised accordingly. No line of the red system of CN will be found in interstellar absorption. The intensity of the red bands in absorption in certain carbon stars in which the violet bands are weak indicates that the atmospheres of these stars have much less continuous absorption in the red than in the violet. [less ▲]

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See detailDoubly ionized rare earths in a2 Canum Venaticorum
Swings, Polydore ULg

in Contributions from the Mount Wilson Observatory (1944), 695

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