Identification of CrH and CrD Molecular Lines in the Sunspot Umbral Spectrum

High-resolution Fourier transform spectrometer sunspot umbral spectra obtained at the National Solar Observatory/Kitt Peak were used to identify molecular rotational lines arising from the infrared band systems of CrH and CrD molecules. Measurement of the equivalent width used the Gaussian-profile approximation method, which is suitable especially for faint lines. Equivalent widths are measured for an adequate number of best lines of the A – X (0,0) band of CrH and the A – X (0,0;1,0) bands of CrD and, thereby, the effective rotational temperatures are estimated.     

The cyanogen bands of Comet Bennett 1970 II

The CN band spectrum of Comet Bennett 1970 II was photographed on April 14, 1970. In addition to the (0,0) band, some other faint lines were observed, which arise either from the (1,1) band of the normal isotopic species or from the (0,0) band of ¹³CN. The Swings effect was investigated theoretically and found to give good agreement with observation. An estimate is made of the pure rotational transition rate in the ground state of CN.Absolute intensities of the CN lines were found by comparison with the lunar spectrum. From these measurements the distribution, density and total mass of cyanogen in the gaseous coma of the comet are estimated.     

The diffuse interstellar bands: a dipolebound state hypothesis

It is proposed that some, possibly many, of the unidentified diffuse interstellar absorption bands arise from rovibronic transitions between the ground states of negatively charged molecules and/or small grains, and shallow dipolebound electronic states which lie close to the electron detachment threshold. Under this hypothesis the attributes for the neutral 'molecular' frameworks are electron affinities between 1 and 3 eV and permanent electric dipole moments of 2 debye or greater. Boundbound spectra involving the lowest rotational levels have not been detected in the laboratory, but these proposed carriers appear to be capable of satisfying the main observational astronomical constraints: transitions that lie in the range from the near-ultraviolet to the near-infrared; a wide range of widths; band wavelengths that are invariant; and a large number of related but distinct carriers. The wavelengths of the lowest rotational lines of the band of the transition between the ground and a dipolebound electronic state of the CH₂CN molecule appear to be consistent with a diffuse band near 8037 Å.     

High-dispersion spectroscopic observations of Venus during 1968 and 1969 II. The carbon-dioxide band at 8689 Å

Thirty well-exposed photographic plates showing the spectrum of the carbon-dioxide band at 8689 Å in the atmosphere of Venus were obtained during 1968 and 1969. All spectra were obtained at a dispersion of 2 Å/mm for Venus phase angles varying from 10° to 126°. We find rotational temperatures ranging from 236 to 274 K. The average value of the rotational temperature is 246 ± 1 K (one standard deviation); for our 1967 observations, the rotational temperatures ranged from 222 to 248 K, with an average value of 238 ± 4 K. The variation of the equivalent width of the 8689 Å band, with Venus phase angle, was very similar for the two sets of observations (53 plates). The temporal variations, of approximately 30% were comparable with the phase variations over this limited range of phase angle.     

Nightglow OH (8, 3) band intensities and rotational temperature at 23°S

The OH (8, 3) band airglow emission has been observed over 1 year at a latitude of 23°S. The average band intensity observed was 385 Rayleighs with a nocturnal range typically less than 100 R. The nocturnal variation in rotational temperature was usually less than 10°K, and the mean temperature was 179°K. The nocturnal variation of intensity is usually uncorrelated with that of the rotational temperature. Time average values of these parameters do, however, show some correlation. On some occasions large post-twilight and pre-dawn intensity enhancements are observed.     

A laboratory discharge lamp source for the O2 atmospheric bands and OI 5577 Å and 6300 Å lines of a known line width

A laboratory discharge lamp is described which strongly emits the forbidden OI 5577 and 6300 Å lines and the O₂ (0?0) atmospheric band. Experimental measurements confirm that these atomic and molecular species are in thermal equilibrium with one another, so that a rotational temperature measurement of the O₂ atmospheric band allows one to deduce the line widths of the 5577 and 6300 Å emissions. This thus provides a useful calibration source for interferometric measurements of these emissions.     

High dispersion observations of Venus during 1972: The CO2 band at 7820Å

Forty-seven well exposed photographic plates of Venus which show the spectrum of the carbon dioxide band at 7820Å were obtained at Table Mountain Observatory in September and October 1972. These spectra showed a semiregular four-day variation in the CO₂ abundance over the disk of the planet (Young et al., 1974). We also find evidence for temporal variations in the rotational temperature of this band and temperature variations over the disk. The two quantities, CO₂ abundance and temperature, do not show any obvious relationship; however, an increase in the temperature usually is accompanied by a decrease in the abundance of CO₂. The average temperature, found from a curve-of-growth analysis assuming a constant CO₂ line width, is 249±1.4K (one standard deviation). This temperature is noticeably higher than the rotational temperature of 242±2K found for this same band in 1967 (Schorn et al., 1969) and of 242±1.2K in 1968–1969 (Young et al., 1971).     

An interpretation of the rotational temperature of the airglow hydroxyl emissions

The rotational temperature of the airglow hydroxyl emissions arising from various schemes of vibrational transitions was obtained by using spectroscopic data from six observational sources. The rotational temperature was found to depend systematically on the quantum number (ν') of the upper vibrational level from which the relevant band originates. It has a doubly degrading characteristic with respect to ν' taking maximal values at ν' = 6 and 9, which exceed considerably the atmospheric temperature. It drops off quickly as ν' decreases from 9 to 7, and then from 6 to 3 after making an abrupt rise at ν' = 6. This ν'-dependence of the rotational temperature is in favor of the hypothesis that there are two routes of excitation of the hydroxyl airglow: O₃ + H = OH(ν ? 9) + O₂, and HO₂ + O = OH(ν ? 6) + O₂. The present result implies also that the relaxation time of rotation of OH in the upper mesosphere is as long as 0.1 sec; a value an order of magnitude larger than that inferred in earlier laboratory experiments.     

A technique to deduce atmospheric temperature and constituent profiles from a planet's limb radiance profile

The concept is described of deducing the temperature and constituent profile of a planetary atmosphere from orbiter measurements of the planet's ir limb radiance profile. Expressions are derived for the weighting functions associated with the limb radiance profile for a Goody random band model. Analysis of the weighting functions for the Martian atmosphere indicates that a limb radiance profile in the 15 μm CO₂ band can be used to determine the Martian atmospheric temperature profile from 20 to 60 km. Simulation of the Martian limb radiance profile in the rotational water vapor band indicates that Martian water vapor mixing ratios can be inferred from limb radiance observations in a water vapor band.     

Rotationally-resolved spectroscopy of Vesta I: 2-4 μm region

We present new infrared (2-4 μm) spectroscopic observations of Vesta obtained in 2001, 2003, and 2004. Together with previously published work, these present a picture of how Vesta's spectrum changes with sub-Earth latitude and longitude. Vesta's albedo and 2-μm band vary regularly with its rotational phase. While establishing the continuum level for Vesta in the 3-μm region is not straightforward, Vesta appears to have a spectrum consistent with the HED meteorites and not requiring a 3-μm water of hydration band. We cannot formally rule out a shallow (∼1%) band, however. We place limits on the extent to which solar-wind implantation and contamination by CM-like impactors has changed the surface spectrum of Vesta.     

Polar cap oh airglow rotational temperatures at the mesopause during a stratospheric warming event

OH (8-3) band rotational temperature was observed at 78.4°N during a stratospheric wanning event. A negative temperature wave of the order of 40 K observed near the mesopause seems to be associated with a corresponding stratospheric warming of the order of 20 K. A 1–2-day delay is observed between the maximum stratospheric warming and the maximum cooling near the mesopause seen in the OH rotational temperature change.     

Measurement of the OH rotational temperature at Mawson,East Antarctica

Measurements of the hydroxyl rotational temperature for the (8, 3) Meinel band are reported for observations made at Mawson, East Antarctica (67° 36′ S, 62° 53′ E) over the austral winter of 1979. Mean values of the rotational temperature are given for 54 nights. The average value lies in the range 160–170 K. The measured temperatures appear lower than those that have been reported at similar latitudes in the Northern Hemisphere. A gradual decrease in the value of the temperature throughout the course of the evening is the only diurnal trend observed. There is little evidence for any impulsive heating associated with auroral activity.     

Spectral properties of hydrogen,helium, methane,and ammonia at thermal infrared wavelengths

We present some results of a theoretical and laboratory program to determine the thermal infrared spectral properties of the principal gaseous constituents of the atmosphere of Jupiter. G. Birnbaum has measured laboratory spectra in the 16 to 1000 um wavelength range for hydrogen and hydrogen-helium mixtures at Jovian temperatures. These are compared to theoretically computed spectra in order to determine the temperature dependence of the line strengths in the pressure-induced rotational band and the overlap parameters from the translational band. Existing spectral data for methane do not agree well with measurements of the ν₄ band at room temperature. A revised allocation of line intensities is proposed. Existing data for the ν₂ (10 um) band of ammonia do agree reasonably well with measurements at room temperature and at ?77δC, but there are some important discrepancies which remain to be explained.     

Saturn in hot water: Viscous evolution of the Enceladus torus

The detection of outgassing water vapor from Enceladus is one of the great breakthroughs of the Cassini mission. The fate of this water once ionized has been widely studied; here we investigate the effects of purely neutral-neutral interactions within the Enceladus torus. We find that, thanks in part to the polar nature of the water molecule, a cold (∼180 K) neutral torus would undergo rapid viscous heating and spread to the extent of the observed hydroxyl cloud, before plasma effects become important. We investigate the physics behind the spreading of the torus, paying particular attention to the competition between heating and rotational line cooling. A steady-state torus model is constructed, and it is demonstrated that the torus will be observable in the millimeter band with the upcoming Herschel satellite. The relative strength of rotational lines could be used to distinguish between physical models for the neutral cloud.     

High-dispersion spectroscopic observations of Venus near superior conjunction: II. The carbon dioxide band at 7883 Å

Nine plates of the 7883-Å CO₂ band were taken between phase angles 7.2 and 10.7° in 1971. A curve-of-growth analysis of 28 rotational lines in the band indicates an average rotational temperature of 236 ± 8°K; the average slope of the curve of growth was 0.63 ± 0.06. The results for this band are compared to those for the 7820-Å band.     

High latitude airglow observations of correlated short-term fluctuations in the hydroxyl meinel 8-3 band intensity and rotational temperature

An application of a tilting filter photometer for the ground-based measurement of the atmospheric temperature at the mesopause altitude (~85km) is described. The technique uses selected rotational emission lines of the OH Meinel night airglow to determine a rotational temperature. A sampling rate of approximately one per minute with a precision of ±5K can be achieved with a field of view (4-km transverse at the mesopause height) sufficient to detect fine structure variations in the temperature and intensity. The systematic error of these measurements is comparable with those of rocket in situ measurements by falling spheres or parachute-borne thermistors. Results obtained March 1974, at Ester Dome, Alaska, indicate the presence of systematic fluctuations in the rotational temperature and the 8-3 band intensity of period 16 min and amplitude 2–4 per cent.     

Inhomogeneities and wavelike variations of the rotational temperature of atmospheric hydroxyl

Quiet and disturbed variations of the rotational temperature of the hydroxyl emissions of the night sky in band 4-1 are described. Examples are given of wavelike propagation of the disturbances of rotational temperature.     

Equivalent width of molecular lines in stars

The expected equivalent widths of the individual rotational lines of (A - X) band of CO and SiO has been calculated for the solar atmosphere. Some of these results are discussed.     

N2 emission in the twilight

About a year's observations of the N₂⁺ band (3914 Å) at Kitt Peak (latitude 32°) are reported. Morning intensities are the same throughout the year, but there is a strong winter maximum in the evening. It is suggested that the additional ionization is produced by photoelectrons from the magnetic conjugate point. Heights are estimated by the zenith-horizon method, which gives 235 km for the constant component and 350 km during the evening enhancement. The intensity variation through twilight is therefore entirely due to changes of the N₂⁺ concentration; each ion scatters light at a constant rate. The rotational distribution resembles that for a temperature of 1600°K, much higher than the temperature of the atmosphere. It is suggested that part of the ions may be produced by charge transfer from metastable O⁺(²D). N₂⁺ concentrations resulting from photoionization are calculated; they give a fair account of the observed horizon intensities, but not the zenith. Non-local electrons from higher in the atmosphere are suggested as a possible extra source; alternatively, the zenith measurements may be perturbed by scattered horizon light. The band intensity in the nightglow cannot be measured; the upper limit is 1 R.     

Infrared spectral observations of asteroid 4 Vesta

An ir spectrum of asteroid Vesta, the first of any asteroid, has been recorded at a spectral resolution of 44 cm^?1 with a Fourier spectrometer. An electronic absorption band is observed that is assigned to an iron-rich pyroxene (pigeonite) spectroscopically similar to that found in certain eucrites. Other important rock-forming minerals such as olivine and plagioclase feldspar are not observed. There is no evidence for compositional variation with rotational phase angle. This spectroscopic picture of Vesta suggests considerable evolution including the melting and differentiation of silicates.