High-resolution atmospheric observations by the Mars Odyssey Thermal Emission Imaging System

High-resolution observations of atmospheric phenomena by the Mars Odyssey Thermal Emission Imaging System (THEMIS) during its first mapping year are presented. An atmospheric campaign was implemented on the basis of previous spacecraft imaging. This campaign, however, proved of limited success. This appears to be due to the late local time of the Odyssey orbit (the locations of activity at 4–6 p.m. appear to be different from those at 2 p.m.). Ironically, images targeting the surface were more useful for study of the atmosphere than those images specifically targeting atmospheric features. While many previously recognized features were found, novel THEMIS observations included persistent clouds in the southern polar layered deposits, dust or condensate plumes on the northern polar layered deposits, dust plumes as constituent parts of local dust storms, and mesospheric clouds. The former two features tend to be aligned parallel and normal to polar troughs, respectively, suggesting a wind system directed normal to troughs and radially outward from the center of the polar deposits. This is consistent with katabatic drainage of air off the polar deposits, analogous to flow off Antarctica. The observation of dust lifting plumes at unprecedented resolution associated with local dust storms not only demonstrates the importance of mean wind stresses (as opposed to dust devils) in initiation of dust storms, but is also seen to be morphologically identical to dust lifting in terrestrial dust storms. As Odyssey moves to earlier local times, we suggest that the atmospheric campaign from the first mapping year be repeated.     

Emission line redshift distribution of QSOs

This paper is the second one of a series of papers on the redshift distribution of QSOs. In this paper, we shall study the influence of the selection effect in the identification of emission lines on the redshift distribution of QSOs more thoroughly than the previous paper (Zhouet al., 1983). If we assume that the QSO's redshift is cosmological, adopt the standard model, and consider the selection effect due to the redshift identification, the limiting apparent magnitude in the observation and the evolutionary effect of QSOs, we can compute the emission line redshift distribution for the so-called optically selected QSOs discovered by objective prism, grating prism technique alone, the QSOs discovered by positional methods or by colour technique and for whole QSOs, respectively (see Figures 6, 11, 12). The results of computation agree with the observations very well, especially for optically selected QSOs; the computational distribution has almost the same shape with the observational one. For this kind of the QSOs the computational distribution may give the positions and heights of all these observed peaks. The correlation coefficient between the calculated and observed distributions is larger than 0.95. It shows that (a) the peaks and dips in the redshift distribution of QSOs are mainly caused by the selection effect in the redshift identification, and (b) the redshift of QSOs is cosmological.     

The excitation of the coronal line 5303 Å

The relation between the intensities of the line 5303 Å and that of the nearby continuum has been investigated at the solar eclipse of March 7, 1970. As this relation depends on the local structure of the corona, spectrograms have been taken at 16 different position angles. For the present investigation, 4 spectrograms have been selected that show the line 5303 Å up to r = 2. The results are presented in Figure 2. For distances r >1.8 the ratio of line-to continuum-intensity, Q, becomes constant. This is the region where the excitation by radiation dominates. Towards smaller distances Q increases as the excitation by collisions becomes more and more important. At r = 1.3 the contributions from both mechanisms are equal. For r <1.3 Q increases stronger than expected for an isothermal and homogeneous model. In the innermost corona the observed values are twice as high as the theoretical ones. This difference can be accounted for by inhomogeneities of the corona.     

Explicit diagram illustrations of the evolution of astrophysical maser line shapes

The astrophysical maser line shape is an important ingredient in analyzing the properties of astrophysical maser sources. Based on a newly developed theory, this paper shows new, detailed, and explicit diagram illustrations of those line shapes and their evolutions.     

The excitation of the infrared atmospheric oxygen bands in the nightglow

Simultaneous observations of the nightgiow emission profiles of $\text{O}{}_2\text{(}{}^1\text{Δ)}$ and the OH Meinel bands have been used to show that the excitation mechanism for $\text{O}{}_2\text{(}{}^1\text{Δ)}$ in the night-time is through the reaction between OH¹ and atomic oxygen and the recombination of atomic oxygen. These reactions, and the proposed rate constants, have been used to derive the atomic oxygen profile appropriate to the observations. It is suggested that the atomic oxygen profile may exhibit significant structure near the mesopause at high latitude. It is also suggested that the extent of this structure may be influenced by transport effects related to stratospheric warming events.     

The interpretation of total line intensities from optically thin gases

We describe a general method for inferring, from the line emission of an optically thin medium, the physical state of the gas along the column in the line of sight which is sampled by the observations. Since it is not possible to infer the distribution of the physical state parameters with position in the line of sight - any arbitrary rearrangement of material giving equivalent line emission - we seek instead to specify the state in another way. A unique specification is found in terms of the bivariate distribution function (n, T), describing the partitioning of the matter in the gas over the density and temperature. We show that, given sufficient observational data, it is in principle possible to determine both (n, T), and the chemical composition. With less complete data the acuity of the analysis is correspondingly reduced.The method is devised for application to the astronomical case, especially for studies of the solar corona, the chromosphere-corona transition region, planetary nebulae and other optically thin sources. We illustrate the formulation for the situation encountered in the solar corona.Presently on leave of absence from the Institute for Astronomy, University of Hawaii.The National Center for Atmospheric Research is sponsored by the National Science Foundation.John Simon Guggenheim Memorial Fellow, 1970.Of the National Bureau of Standards and the University of Colorado.     

On the calculation of spurious velocity signal produced by atmospheric differential extinction in whole-disk oscillation measurements

The systematic diurnal signal drift in full-disk solar oscillation measurements has been calculated taking into account differential rotation, the inclination of the rotational axis of the Sun with respect to the picture plane, the limb-darkening function and a realistic estimation of the sky transparency, slightly variable during the day. An illustration of this method on the Kumbel (U.S.S.R.) IRIS data is presented and discussed.     

Emission line velocity survey of spiral galaxies with bright nuclei

High resolution spectrographic observations of 220 nearby galaxies with bright nuclei have been made mainly at H and [Oiii] 5007 to search for signs of nuclear activity. In many cases evidence for weak activity has been found.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Emission line widths of an asymmetric bowshock inside a cloud of dust

A model is presented that explains the anomalous emission line widths in the Herbig-Haro object HH 1 in terms of emission from a lop-sided bowshock and scattering by surrounding dust.     

The excitation of the 557.7 nm line and Herzberg bands in the nightglow

Measurements of the emission intensities of the 557.7 nm line and Herzberg bands and of O(³P) concentrations carried out on two coordinated rocket flights at South Uist during the night of 8/9 September 1975 are presented. An examination of the 557.7 nm emission and $\text{O}\text{(}{}^3\text{P}\text{)}$ data on the basis of recent data on relevant rate coefficients has shown that the results can be interpreted on the basis of the Barth mechanism for the production of $\text{O}\text{(}{}^1\text{S}\text{)}$ atoms but not the Chapman mechanism. Evidence is provided that the A³Σ⁺_u state of O₂ could be responsible for the $\text{O}\text{(}{}^1\text{S}\text{)}$ production in the Barth mechanism. Values of the rate coefficients involved are deduced from a comparison of the 557.7 nm and Herzberg emission rates.     

Emission line ratios for Fexxi applicable to the XUV spectra of solar flares

Electron impact excitation rates for Fexxi, calculated with theR-matrix code, are used to determine theoretical electron density sensitive emission line ratios involving transitions in the 121–146 wavelength range. The observed ratios for a solar flare, obtained with a grazing spectrometer on board the OSO-5 satellite, imply electron densities which are consistent, with discrepancies that do not exceed 0.3 dex. In addition, the derived values ofN _e are similar to those estimated for the high temperature regions of other solar flares. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations.     

The atmospheric entry of fine‐grained micrometeorites: The role of volatile gases in heating and fragmentation

The early stages of atmospheric entry are investigated in four large (250–950 μm) unmelted micrometeorites (three fine‐grained and one composite), derived from the Transantarctic Mountain micrometeorite collection. These particles have abundant, interconnected, secondary pore spaces which form branching channels and show evidence of enhanced heating along their channel walls. Additionally, a micrometeorite with a double‐walled igneous rim is described, suggesting that some particles undergo volume expansion during entry. This study provides new textural data which links together entry heating processes known to operate inside micrometeoroids, thereby generating a more comprehensive model of their petrographic evolution. Initially, flash heated micrometeorites develop a melt layer on their exterior; this igneous rim migrates inwards. Meanwhile, the particle core is heated by the decomposition of low‐temperature phases and by volatile gas release. Where the igneous rim acts as a seal, gas pressures rise, resulting in the formation of interconnected voids and higher particle porosities. Eventually, the igneous rim is breached and gas exchange with the atmosphere occurs. This mechanism replaces inefficient conductive rim‐to‐core thermal gradients with more efficient particle‐wide heating, driven by convective gas flow. Interconnected voids also increase the likelihood of particle fragmentation during entry and, may therefore explain the rarity of large fine‐grained micrometeorites among collections.     

Enhancement of the solar X-ray line intensities due to dielectronic recombination as an excitation process

Intensities of resonance lines in X-ray region for Si ix–Si xiv ions are calculated by considering total excitation, i.e., excitation due to electron impact and dielectronic recombination. It is found that the contribution of the latter is quite significant. For consistency, the electron density effect in our calculations is not only accounted for in the ionization equilibrium but also in the total rate of excitation. It is also found that the contribution of electron density effect is pronounced with the inclusion of dielectronic recombination as an excitation mechanism. The computed average line intensities are compared with the available observations and a table of line flux for various wavelengths of the above-mentioned ions at different temperatures is also given.     

Generation of atmospheric turbulence by solar radiation

A statistical framework of weak turbulence is applied to investigate the maintenance of atmospheric turbulence during a long period, even after the external energy supply from solar radiations has stopped. Thus, the problem of hydrodynamical turbulence without any mean motion is dealt with. Main attention is drawn to one-dimensional Burgers equation, together with a discussion devoted mainly to Millionshtchikov's hypothesis, which may be applied as a consequence of the assumed weak turbulence. Remarkably, this leads to an explicit proof of the existence of the cascade process in turbulence. The results are illustrated by numerical calculations.On study leave from the Department of Physics, M.S. College, Subaranpur, U.P., India.     

Collision-induced rotational excitation of interstellar molecules using the Effective Straight line Trajectory (EST) approach

The Effective Straight-line Trajectory (EST) approach suggested earlier for computation of collision-induced linewidths and rates has been used further for some more systems of interstellar interest. These systems are X-He, X-H, and H-H₂ where X are interstellar molecules CO, SiO, HCN, and HC₃N.     

The excitation of Fe XVII by electron impacts

The cross-sections for the excitation of Fe XVII are computed using the Coulomb-Born approximation. For the excitation of the configurations 2p⁵ 3s, 2p⁵ 3p and 2p⁵ 3d, the intermediate coupling scheme is used, while an extrapolation is made for the excitation of the 2s 2p⁶ 3s, 2s 2p⁶ 3p and 2s 2p⁶ 3d configurations from the results obtained earlier in the lithium-like ions. It is found that the excitation cross-section Q (2p^{6 1}S₀2p⁵ 3p ¹S₀) is fairly large and partly removes the disagreement between the theoretical and experimental intensity-line ratios.Work supported in part by the Advanced Research Projects Agency (Project DEFENDER) monitored by the U.S. Army Research Office, Durham, N.C., under Contract DA-31 -124-ARD-D-139.Research Associate at J.I.L.A., Boulder, Colo., for the year 1965–1966.NASA-ESRO fellowship at the University of Colorado, Boulder, for the year 1965–1966.