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Ultraviolet and visible spectroscopy of comets has identified a large number of species in the coma, most of which appear to be the photodissociation and photoionization products of the “parent” molecules evaporated directly from the cometary nucleus. Analyses of cometary spectra support the icy conglomerate model of the nucleus with H2O as the dominant ice species. Two molecules detected in the ultraviolet, CO and S2, are of particular interest to the study of the cosmogonic evolution of cometary grains. CO appears to be a highly variable constituent from comet to comet, while S2, first observed in comet IRAS-Araki-Alcock in 1983, is found in no other celestial source. Both of these molecules appear to be parent molecules.
Excavations at the 109 hectare site of Kurd Qaburstan on the Erbil plain in the Kurdistan Region of Iraq were conducted by the Johns Hopkins University in 2013 and 2014. The Middle Bronze Age (Old Babylonian period) is the main period of occupation evident on the site, and the project therefore aims to study the character of a north Mesopotamian urban centre of the early second millennium b.c. On the high mound, excavations revealed three phases of Mittani (Late Bronze) period occupation, including evidence of elite residential architecture. On the low mound and the south slope of the high mound, Middle Bronze evidence included domestic remains with numerous ceramic vessels left in situ. Also dating to the Middle Bronze period is evidence of a city wall on the site edges. Later occupations include a cemetery, perhaps of Achaemenid date, on the south slope of the high mound and a Middle Islamic settlement on the southern lower town. Faunal and archaeobotanical analysis provide information on the plant and animal economy of the second millennium b.c. occupations, and geophysical results have documented a thirty-one hectare expanse of dense Middle Bronze Age architecture in the northern lower town.
The UVX experiment has resulted in confirmation that the diffuse ultraviolet background is low in intensity everywhere and that it is fairly uniform in intensity, both spatially and spectrally. There is no clear evidence that any significant portion of the moderate galactic latitude diffuse cosmic background originates in galactic plane starlight scattering from interstellar dust.
Firestone & Scholl (F&S) rely on three problematic assumptions about the mind (modularity, reflexiveness, and context-insensitivity) to argue cognition does not fundamentally influence perception. We highlight evidence indicating that perception, cognition, and emotion are constructed through overlapping, distributed brain networks characterized by top-down activity and context-sensitivity. This evidence undermines F&S's ability to generalize from case studies to the nature of perception.
A flare of size M8 occurred while SUMER was recording a spectral scan above the active region NOAA 8537 at the west limb. We recorded spectra during the pre-flare phase, at flare onset, and during the decay phase of this main flare in a series of events. More than 60 flare lines were identified during this observation, which include Fe XVIII - Fe XXIII lines that provide evidence of 107 K plasmas. We also recorded lines from He-like ions, such as Ne IX, Na x, Mg XI, and Si XIII. Accurate wavelength measurements of such lines are of interest in basic atomic physics studies. Using plasma diagnostic techniques, we investigated the temporal evolution of the electron densities and temperatures during the event.
The past three years have seen not only a growth in the activities of our commission, but an extension of its activities into important areas which have heretofore motivated too little activity. Of particular interest have been the many activities directed towards elucidating the question of the abundance of extrasolar planetary systems. There have been a number of observations showing the presence of disks of dust around nearby stars, disks which fit the idea that stars are often formed with an accompanying disk of dust which may in many or perhaps all cases produce a planetary system. Infra-red evidence for dust disks exists for something like twenty stars. The disk of Beta Pictoris has even been clearly imaged at optical wavelengths, showing without a doubt that such disk structures exist. One very impressive detection of an apparent brown dwarf object has also been made; should this be confirmed by other observations, it would be clear evidence for the existence of planet-like bodies in the systems of other stars.
The present report of Commission 15 has been, as usual, prepared primarily by the chairpersons of the two working groups. E. Tedesco wrote the section about Asteroids and Meteorites, with the assistance of A. Cellino, G. Consolmagno and C.-I. Lagerkvist. W. F. Huebner prepared the section about Comets, with the assistance of J. Benkhoff, H. Boehnhardt, J. Brandt, M. T. Capria, A. Cochran, G. Cremonese, M. Duncan, W. Huntress, H. Levison, and G. P. Tozzi. Moreover, the whole document has been assembled by K. Muinonen, who did the final editing, to merge the two reports and fit the document into the allotted space. Material taken from both major areas regarding the relationship between comets and asteroids has been combined into a single section.
During the past decade, vacuum ultraviolet spectra of over 30 comets have been obtained with the International Ultraviolet Explorer (IUE) satellite observatory. With few exceptions, the spectra of these comets appear to be similar, with OH and H produced by the photodissociation of water being the dominant species and emissions of C, O, S, CS and CO+2 usually present. Although signs of variability of many kinds in comet spectra appear, the evidence from the ultraviolet observations suggests that all comets have the same basic chemical composition and that observed differences are due to evolution and ageing processes. The principal exception is S2, which was detected by IUE in comet IRAS-Araki-Alcock (1983 VII), but not in any other comet to date. During the 1985–86 apparition of comet Halley, ultraviolet spectra were also obtained by other spacecraft and by sounding rocket instruments, including a long-slit imaging spectrograph. Further advances await future ultraviolet observations of comets by the Hubble Space Telescope and other planned ultraviolet astronomy missions.
The recent observations of atomic oxygen and carbon in the far ultraviolet spectrum of Comet Kohoutek (1973f) (Feldman et al. 1974; Opal et al. 1974) have demonstrated the existence of these atomic species in the cometary coma. However, in order to identify the source of their origin, it is necessary to relate the observed ultraviolet flux to the atomic production rate. Assuming the only excitation mechanisms allowed are those produced by resonance scattering and fluorescence of solar ultraviolet radiation, the problem reduces to finding the emission rate factors (g-factors) as a function of the heliocentric comet velocity. Since the widths of the solar emission lines are smaller than the maximum heliocentric Doppler shift, given by
where q is the perihelion distance in A.U., it is necessary to consider the detailed multiplet structure of the transition, the solar line shape and the relaxation of excited fine structure levels.