Near-infrared imaging in H2 of molecular (CO) outflows from young stars

We have imaged several known molecular (CO) outflows in H₂ v=1-0 S(1) and wide-band K in order to identify the molecular shocks associated with the acceleration of ambient gas by outflows from young stars. We detected H₂ line emission in all the flows we observed: L 1157, VLA 1623, NGC 6334I, NGC 2264G, L 1641N and Haro 4-255. A comparison of the H₂ data with CO outflow maps strongly suggests that prompt entrainment near the head of a collimated jet probably is the dominant mechanism for producing the CO outflows in these sources.     

Signatures of solar wind interaction with the nightside ionosphere of Venus

Plasma and field relationships observed across the nightside of Venus evidence a chaotic variety of interactions between the ionosphere and the combined effect of the solar wind and interplanetary magnetic field draped about the planet. Close examination of these data reveal within the chaos a number of repeatable signatures key to understanding fundamental field-plasma interactions. Observed from the Pioneer Venus Orbiter, (PVO), nightside conditions range from extensive, full-up ionospheres with little evidence of dynamic or energetic perturbations, to an almost full depletion, sometimes described as disappearing ionospheres. Between these extremes, the ionospheric structure is often irregular, sometimes exhibiting well-defined density troughs, at other times complex intervals of either abundant or minimal plasma concentration. Consistently, large B-fields (typically exceeding 5–10 nanoteslas) coincide with plasma decreases, whereas stable, abundant plasma distributions are associated with very low-level field. We examine hundreds of nightside orbits, identifying close correlations between regions of elevated magnetic fields featuring polarity reversals, and (a) exclusive low-frequency or distinctive broadband noise, or both, in the electric field data, (b) turbulent, superthermal behavior of the the ions and electrons. We review extensive studies of nightside fields to show that the correlations observed are consistent with theoretical arguments that the presence of strong magnetic fields within normal ionospheric heights indicates the intrusion of magnetosheath fields and plasma within such regions. We find abundant evidence that the ionosphere is frequently disrupted by such events, exhibiting a chaotic, auroral-like complexity appearing over a wide range of altitude and local time. We show that field-plasma disturbances, widely suggested to be similar to conditions in the Earth's auroral regions, are tightly linked to the electric field noise otherwise attributed to lightning. Owing to the coincidence inherent in this relationship, we suggest that natural, predictable plasma instabilities associated with the plasma gradients and current sheets evident within these events produce the E-field noise. The data relationships argue for a more detailed investigation of solar wind induced E-field noise mechanisms as the appropriate scientific procedure for invoking sources for the noise previously attributed to lightning. Consistent with these views, we note that independent analyses have offered alternative explanations of the noise as arising from ionospheric disturbances, that repeated searches for optical evidence of lightning have found no such evidence, and that no accepted theoretical work has yet surfaced to support the inference of lightning at Venus.     

Phosphine absorption in the 5-μm window of Jupiter

Since the original suggestion by Gillett et al. (1969) it has generally been assumed that the region of partial transparency near 5 μm in Jupiter's atmosphere (the 5-μm window) is bounded by the v₄ NH₃ at 6.1 μm and the v₃ CH₄ band at 3.3 μm. New measurements of Jupiter and of laboratory phosphine (PH₃) samples show that PH₃ is a significant contributor to the continuum opacity in the window and in fact defines its short-wavelength limit. This has important implications for the use of 5-mu;m observations as a means to probe the deep atmospheric structure of Jupiter. The abundance of PH₃ which results from a comparison of Jovian and laboratory spectra is about 3 to 5 cm-am. This is five to eight times less than that found by Larson et al. [Astrophys. J. (1977) 211, 972–979] in the same spectral region, but is in good agreement with the result of Tokunaga et al. [Astrophys. J. (1979) 232, 603–615] from 10-μm observations.     

Some comments on the limb shift of solar lines

We searched for a variation with heliographic latitude of the solar limb effect by comparing the relative wavelengths of weak and strong Fraunhofer lines. The blue shifts associated with the limb effect appear 9%±5% larger in the polar radius vector than in an equatorial radius vector at cos = 0.5. This should perhaps be interpreted as an increase with latitude of either solar convection or of convective overshoot. Recent observations of poleward meridional flows of 30m s^–1 should be corrected for this limb effect variation. This correction increases this flow velocity to 70 m s^–1. A search for a similar variation in plages and in network boundaries had negative results, the variation being +1%±5% and -1%±6% respectively.Now at the Multiple Mirror Telescope Observatory, University of Arizona, Tucson, Ariz. 85721, U.S.A. The MMTO is jointly operated by the University of Arizona and the Smithsonian Institution.The Sacramento Peak Observatory is operated by the Association of Universities for Research in Astronomy, Inc. under contract AST 78-17292 with the National Science Foundation.     

Carbon isotopic fractionation between CO2 vapour,silicate and carbonate melts: an experimental study to 30 kbar

The carbon isotopic fractionation between CO₂ vapour and sodamelilite (NaCaAlSi₂O₇) melt over a range of pressures and temperatures has been investigated using solid-media piston-cylinder high pressure apparatus. Ag₂C₂O₄ was the source of CO₂ and experimental oxygen fugacity was buffered at hematite-magnetite by the double capsule technique. The abundance and isotopic composition of carbon dissolved in sodamelilite (SM) glass were determined by stepped heating and the ¹³C of coexisting vapour was determined directly by capsule piercing. CO₂ solubility in SM displays a complex behavior with temperature. At pressures up to 10 kbars CO₂ dissolves in SM to form carbonate ion complexes and the solubility data suggest slight negative temperature dependence. Above 20 kbars CO₂ reacts with SM to form immiscible Na-rich silicate and Ca-rich carbonate melts and CO₂ solubility in Na-enriched silicate melt rises with increasing temperature above the liquidus. Measured values for carbon isotopic fractionation between CO₂ vapour and carbonate ions dissoived in sodamelilite melt at 1200°–1400° C and 5–30 kbars average 2.4±0.2, favouring¹³C enrichment in CO₂ vapour. The results are maxima and are independent of pressure and temperature. Similar values of 2 are obtained for the carbon isotopic fractionation between CO₂ vapour and carbonate melts at 1300°–1400° C and 20–30 kbars.     

Distribution and relations of 4- to 10-km-diameter craters to global geologic units of Mars

By correlating the 1:25,000,000 geologic map of Mars of Scott and Carr (1977) with 4- to 10-km-diameter crater density data from Mariner 9 images, the average crater density for 23 of the equatorial geologic-geomorphic units on Mars was computed. The correlation of these two data sets was accomplished by digitizing both the crater density data and geologic map at the same scale and by comparing them in a computer. This technique assigns the crater density value found in the corresponding location on the geologic data set to a discrete computer file assigned each of the 23 geologic units. By averaging the crater density values accumulated in each file, an “average” crater density for each geologic unit was obtained. Condit believes these average crater density values are accurate indicators of the relative age of the geologic units considered. The statistical validity of these average values is strongest for the geologic units of the largest areal extent. The relative ages as obtained from the average crater density values for the seven largest geologic units, from youngest to oldest, are: Tharsis volcanic material, 21 ± 4 craters/10⁶km²; smooth plains material, 57 ± 14 craters/10⁶km²; rolling plains material, 66 ± 16 craters/10⁶km²; plains materials, 80 ± 17 craters/10⁶km²; ridged plains material, 128 ± 25 craters/10⁶km²; hilly and cratered material, 137 ± 38 craters/10⁶km²; and cratered plateau material, 138 ± 27 craters/10⁶km².     

Magnetostratigraphic evidence from the Cold Creek bar for onset of ice-age cataclysmic floods in eastern Washington during the Early Pleistocene

This study provides a detailed magnetostratigraphy of sediments composing the Cold Creek cataclysmic flood bar in the Pasco Basin, Washington. Our interpretation suggests onset of Missoula floods or similar events prior to 1.1 myr, later than previously suggested by Bjornstad et al. [Bjornstad, B.N., Fecht, K.R., Pluhar, C.J., 2001. Long history of pre-Wisconsin, Ice Age cataclysmic floods: evidence from southeastern Washington State. Journal of Geology 109 (6), 695-713]. Nonetheless these data suggest that Channeled Scabland features formed over a much longer timespan than commonly cited, that continental ice sheets of the early Pleistocene reached as far south as those of the late Pleistocene, and that similar physiography existed in eastern Washington and perhaps Montana to both generate and route Missoula-flood-like events. This study adds paleomagnetic polarity results from 213 new samples of silts and sands derived from nine new drill cores penetrating the Cold Creek cataclysmic flood bar to our previous database of 53 samples from four boreholes, resulting in a much more robust and detailed magnetostratigraphy. Rock magnetic studies on these sediments show pure magnetite to be the predominant remanence-carrying magnetic mineral, ruling out widespread remagnetization by secondary mineralization. The magnetostratigraphy at eastern Cold Creek bar is characterized by a normal polarity interval bracketed by reversed polarities. Equating the normal zone with the Jaramillo subchron (0.99-1.07 myr) affords the simplest correlation to the magnetic polarity timescale. Western Cold Creek bar was likely deposited during the Brunhes chron (0-0.78 myr) since it exhibits mainly normal polarities with only two thin reversed-polarity horizons that we interpret as magnetic excursions during the Brunhes.     

Biofouling and the continuous monitoring of underwater light from a seagrass perspective

For more than a decade, inexpensive electronic instruments have made continuous underwater light monitoring an integral part of many seagrass studies. Although biofouling, if not controlled, compromises the utility of the record. A year-long assessment of the time course of sensor fouling, in the Laguna Madre of Texas established that light transmitted through the fouling layer after 2 wk of exposure exceeded 90% except for a 6–8 wk period in May and June. On that basis, a 2-wk interval was chosen for routine servicing. Subsequent monitoring proved this choice to be grossly in error. The period of sub-90% transmittance after 2 wk extended to 4–6 mo annually over the next 3 yr. Fouling was strongly correlated with temperature, ambient light, and year. Since an algal bloom of 7-yr duration finally waned during this study, increased ambient light seemed most likely to explain increased fouling later in the study. The explanatory value of light was less than temperature or year in multiple regression, requiring some other explanation of the date effect than change in ambient light. Allelopathic and suspension-feeding depressant effects of the brown tide are offered as the most likely cause of unusually low fouling in the first year. Biofouling was so unpredictable and rapid in this study that at least weekly maintenance would be required to assure reliability of the light monitoring record.