OI Line Research Articles

Retrieval of atomic oxygen and temperature in the thermosphere. II—feasibility of an experiment based on limb emission in the OI lines

A viable technique for remote sensing of the atomic oxygen density and translational temperature profiles above 80 km altitude, where oxygen atoms are involved in important chemical, collisional and radiative cooling processes, would have enormous value. The two profiles can, in principle, be recovered simultaneously from limb scan data obtained near wavelength 147 μm and/or 63 μm, corresponding to the intermultiplet transitions in the ground electronic state of atomic oxygen. Part I of this paper (1989, Planet. Space Sci. 37, 1333) considered an approach in which the limb radiance data represent just one of the lines observed at high spectral resolution; recovery of the temperature relies mainly on Doppler broadening. Here, in Part II, we evaluate feasibility of the experimental concept when the data are a pair of limb radiance profiles corresponding to the two unresolved OI lines; temperature retrieval relies mostly on the difference in upper state populations. O-atom density and translational temperature profiles were retrieved from noise-contaminated synthetic data by an inversion procedure that uses both the onion peeling and global-fit methods. The latter allows solutions to be obtained despite the occurrence of a singular Jacobian, typically at 200 km tangent height. It is concluded that stable profiles for the altitude range 90–300 km can be recovered when the noise-equvalent radiances in the two channels are no greater than roughly 10 −13 W cm −2 sr −1. We estimate that this level of sensitivity could be achieved in a small space-borne cryogenic sensor based on non-scanning Fabry-Perot etalons. The spectrally-resolved approach described in Part I required a considerably larger, more advanced sensor.

Retrieval of atomic oxygen and temperature in the thermosphere. I — Feasibility of an experiment based on the spectrally resolved 147 μm limb emission

The importance of atomic oxygen and translational temperature in mesospheric/thermospheric processes is the motivation to study the feasibility of recovering vertical profiles of the temperature and O-atom density from limb scan data obtained near 147 μm and/or 63 μm wavelength, corresponding to the oxygen atom ground electronic state (OI) transitions. The limb radiance data must be spectrally resolved to recover both temperature and atomic oxygen density if only one of the OI lines is used, which is the approach investigated in this paper. We show how the two vertical profiles can be recovered by applying an onion-peeling method to synthetic data. The temperature and O-atom density in each peeled layer are obtained simultaneously by non-linear least-squares spectrum fitting. Spectral data in the 147 μm line was found to yield reasonably accurate and stable profiles from 300 km down to an altitude between 130 and 90 km, depending on the noise level and spectral resolution, and gave better results than the stronger 63 μm spectral data below 140 km. We estimate that the S/N and spectral resolution required for successful retrievals could be provided by a confocal Fabry-Perot system operating near 147 μm, although retrievals down to 90 km from data obtained at orbital altitude would require cooled foreoptics roughly a meter in diameter. The forthcoming Part 2 will show that the alternative approach, based on limb radiance data for both OI lines, not spectrally resolved, can be implemented with a much smaller telescope and the conventional parallel design for the Fabry-Perot etalons.

Interpretation of the CO Bands of Supernova 1987A

AbstractModel calculations for the interpretations of the CO bands in the IR are discussed. Spherical symmetry is assumed. Profiles of the physical quantities (i.e. temperature, mass, electron density, abundances, etc.) are given by NLTE models which allow for the representation of observed spectra of supernova 1987A in the optical and near infrared. C and O have to be chosen overabundant by a factor of 25 in the helium-rich layers, or a clumpy density distribution structure of a corresponding factor relative to the mean local value is needed. However, the comparison between the observed forbidden OI line at about 6300 A favours the first interpretation. A factor of about 3 has to be taken into account as uncertainty for the overabundance because of the assumptions of the background model. This implies evidence for strong mixing of the helium rich region with more central layers during the stellar evolution and/or the explosion.

Excitation of 557.7 nm OI line in nightglow

Using nightglow data the mean values that the rate coefficients of the energy transfer processes yielding O( 1S) must have if O 2( c), O 2( A), O 2( A′) or O 2( 5Π g) is to be the main precursor to the green are calculated. These values, combined with measurements that Slanger and Black (1976b, J. chem. Phys. 64, 3767) have made on oxygen-argon afterglows, seem to exclude O 2( A) or O 2( A′) from being the precursor but are consistent with O 2( c) being the precursor. Some results on O( 1S) deactivation may be relevant to the O 2( c) precursor hypothesis. The question of whether or not O 2( 5Π g) is a significant precursor to the green line in the nightglow is left unanswered.

Abundances in Stars in Globular Clusters from Palomar CCD Spectra

We have completed abundance analyses of stars in three globular clusters: M71, M4. and M22. Spectra of resolution 0.3 and 0.6 (two pixel) resolution have been obtained with the Palomar coudé spectrograph and a TI CCD. The analysis was carried out with model atmospheres and f-values derived from three sources: absolute f-values derived by theory for the 6300 line of OI and for CN bands, laboratory f-values for lines that are too weak in the sun to be useful, and solar f-values. The last introduce an uncertainty of about 0.25 dex because solar f-values derived via the Holweger-Muller model differ from those derived via the BEGN model.

Neutral oxygen in herbig Ae stars

In stars with dense envelopes such as classical Be and T Tauri stars, the near infrared lines of OI have been observed: λ 8446 Å in emission, λ 7772 Å in absorption or in emission (e.g. Polidan and Peters, 1976; Herbig and Soderblom, 1980). In Herbig stars, only low resolution (2-7 Å) material is available on a few objects (Shanin et al. 1975; Andrillat and Swings, 1976).

A model for the Cl (609 μm) emission of Orion

A model for the energy balance and chemical equilibrium of the gas in photodissociation regions at the edge of molecular clouds, which are illuminated by strong FUV fields (6 eV ≦ hv ≦ 13.6 eV), has been developed. This model is used to calculate the emergent intensities in the fine structure lines of OI (63 μm, 145 μm), CI (609 μm, 370 μm), and CII (158 μm) and in the low-lying rotational transitions of CO. The numerical results show that column densities in the range 2 × 10 17 to 2 × 10 18 cm 2 can be expected from the C +/C/CO transition region at the edge of molecular clouds. This difference with previous chemical calculations is partly due to a higher assumed carbon abundance, partly due to the charge exchange reactions of C + with S and SiO, and partly due to carbon self-shielding which is taken into account. A detailed model is constructed for the Orion photodissociation region, which explains the observed OI (63 μm, 145 μm), CII (158 μm), CI (609 μm), and CO emission. In this model the CI (609 μm) emission originates in the warm (50°K) molecular gas behind Θ 1C Ori but near the surface of OMCI.

SEC Vidicon Spectra of Geminid Meteors, 1972

The SEC Vidicon, a low light level closed circuit television system, was used to obtain 137 spectrographic records of meteors at Mt. Hopkins, Arizona, during the Geminid meteor shower in December 1972. Seven of the best Geminid meteor spectra are studied here in detail. The near infrared, out to wavelengths near 9000 Å, is recorded for the first time for Geminids. The spectra, in general, exhibit the elements previously found in photographic records of this shower but show a surprising frequency of occurrence of the forbidden green line of OI at 5577 Å. This line is normally absent from meteors moving as slowly as the Geminids (36 km/s) and its presence in these records may be due to the added sensitivity available with the SEC Vidicon. The average green line duration in Geminid meteors with a luminosity near zero absolute visual magnitude is 0.73 s at a mean height of 95 km, 11 km lower than the green line peak in Perseid meteors of the same luminosity.

Calculation of the thermal excitation functions for plasmas developing under various conditions

The thermal excitation functions are calculated for several HI, OI, NI, Ci, XeI, and XeII lines for H2, O2, N2, CO2, and Xe plasmas, respectively, produced in closed systems, and the HI, NI, and OI lines for freely developing H2, N2, and O2 plasma. It is shown that the behavior of the thermal excitation functions is strongly influenced by the plasma-development conditions.

Electrical conductivity and total emission coefficient of air plasma.

The electrical conductivity, o-, and the total radiant power per unit volume, PR9 of air are measured for temperatures between 8,000 and 12,500°K at atmospheric pressure. The measurements are made in a wallstabilized electric arc discharge which produces a pure, stable plasma. Axial electric field strength, £,, and azimuthal magnetic field intensity, B^ are measured as functions of the discharge radius by using probe techniques. Current density, jz9 is obtained as ~]*= V x£//z0, and electrical conductivity is determined by using Ohm's law, o = jJEz. PR is measured with a total radiation thermopile and also by using an electrical technique. Plasma temperature is determined from the absolute intensities of the 4935 A NI and 4368 A OI lines.

Narrow Band Photometry of Supergiant Stars

At the National Astronomical Observatory in San Pedro Mártir, B. C. (Mexico), we have performed photoelectric photometry for 31 stars in a narrow-band system. The system allows the measurements of total absorptions of neutral oxygen at 7774 Å through three interference filters (20–25 Å half-width), one for the OI lines and two for the continuum.The preliminary results are very encouraging: Supergiant stars, ranging in spectrum from the later subdivisions of type B to early G, can be clearly separated from other luminosity classes. The total absorptions depend strongly on the stellar luminosity and, to a lesser degree on the effective temperature (spectral type) of the star. The system may be improved by using narrower filters and detectors with a higher quantum efficiency, already in existence.

Observations spectroscopiques de HD 50138

Observations of the Be star HD 50138 have been extended to the photographic infrared region up to 9500 A. The main features noted in this wavelength range are strong lines of Oi (8446 A), Hi (from P 9 to P 20), the Caii infrared triplet and the λ8629 line attributed to Ni. The λ7772 multiplet of Oi is shown to undergo important changes during the period of observations (1959–1971). Higher Balmer lines do not exhibit any emission component, but their profiles are variable and indicate the presence of satellite absorption, as already mentioned by some authors.

Electric discharges in air: Near infrared emission spectrum

The emission from glow discharges in flowing air has been investigated in the 1–5 μ wavelength region with a vacuum spectrometer. Most of the spectral features observed in the pressure range of 1 2 -10 torr are identified, including atomic lines of OI, NI and HI; molecular bands of N 2, NO, N 2O, CO 2 and CO. The spectra are presented as a function of pressure and a table compiled of the atomic lines. Of particular interest are the contrasts between the emission of the air discharge and that of the pure gases, nitrogen and oxygen. In addition, the results of studied of several discharge modes, employing steady voltages and pulsed, provide data on details of the energy flow within the plasma. Pulsed discharges, for example, commonly give rise to emission from the infrared active species N 2O and CO 2 that is more intense in the afterglow than in the glow.

Brightness of forbidden OI lines and properties of shadow bands during the eclipse of 7 March 1970

During the total eclipse of 7 March 1970 two types of measurements were made at a site in the center of the eclipse track at Dam Neck, Virginia. The OI forbidden 5577 Å and 6300 Å lines were measured looking vertically through the eclipse shadow. The intensities were approximately 1 kilorayleigh, essentially the values obtained in recent rocket measurements of normal day airglow at altitudes above 100 km. This is consistent with the hypothesis that these lines originate primarily at altitudes well above the shadow from mechanisms which are not appreciably perturbed by the approaching shadow. Measurements were also made of the time variation of intensity of incident light during the shadow-band period before second contact. There are saw-tooth fluctuations with steep leading edges, as well as many high frequency components of smaller amplitude. This time variation does not appear to be obviously related in a simple way to current theories of their production mechanisms, or to the visual appearance of shadow bands.

Day airglow emissions of 5577 A and 6300 OI lines In Martian atmosphere

In this paper emissions of 5577 A and 6300 A lines of OI in Martian atmosphere have been investigated. It has been found that for the 5577A line there are two peaks at 90 and 120 km and its total intensity is about 3.5 kR. For the 6300A line, since the rate of quenching by CO2 molecules is not known, its emission profile is obtained for two values of quenching coefficient, namely, 1 X 10-13 cm3 sec-1 and 1 X 10-12 cm-3 sec-1. It has been found to have a broad peak at 100-.140 km. Its intensity has been found to be 3 and 1 kR for the two values of rate coefficient.

Laboratory Emission of OI Line λ5577

Experimental conditions under which the OI line λ5577 is emitted in a low-pressure glow discharge tube containing a mixture of oxygen and xenon gas is studied. It is clear from the experimental data that the excited xenon atom acts only upon the oxygen molecule and not upon the oxygen atom. On the basis of this study, it is proposed that the emission mechanism of OI line λ5577 should be classified into two processes: A. initial process, Xe″+O2(x3Σ-g)→Xe(1S0)+O(3P)+O(1S0)(Xe″ indicates a higher excited state of xenon) and B. main process, Xe*(3P2)+O2(a1Δg)→Xe(1S0)+O(3P)+O(1S0).This emission mechanism is different from the mechanism which uses the reaction of argon with a small amount of oxygen in a discharge tube.

Elargissement et deplacement par effet stark de raies de l'atome neutre d'oxygene

The broadening and displacement caused by the Stark effect have been studied for infrared lines of OI emitted from a plasma produced by induction heating. Comparisons have been made between the measurements and calculations using both existing semi-classical theories and a quantitative analysis in which a better determination is made of the contributions of strong collisions. The new calculations agree well with observed broadening effects and fairly well with the measured line displacements.

Infrared Electronic Emission Spectrum of Oxygen

The emission spectrum of the positive column of an electric discharge in flowing oxygen has been investigated in the near ir, from 1-micro to 5-micro wavelength. Spectra over a range of pressures from 0.5 Torr to 10 Torr are displayed, and thirteen previously unreported lines of OI measured and assigned. The stronger ir lines are discussed as probable auroral emission features, and the levels 5g(3,5)G(0) of OI are established. Infrared active molecular impurity species present in the oxygen discharge indicate a vibrational temperature in excess of 2000 K, as is also the case for nitrogen discharges under similar conditions. Unlike the nitrogen discharge, that of the oxygen emits an ir spectrum consisting only of atomic lines and is, furthermore, notably deficient in visible emission.

The relationship between variations of solar corpuscular and ultra-violet radiation and the intensity of the midlatitude airglow in the OI line (λ 5577 Å)

The relationship between variations of solar corpuscular and ultra-violet radiation and the intensity of the midlatitude airglow in the OI line (λ 5577 Å)

The forbidden lines of OI in the photospheric spectrum

The forbidden lines of OI in the photospheric spectrum