A survey of meteor spectra and orbits: evidence for three populations of Na-free meteoroids

We present a survey of 97 spectra of mainly sporadic meteors in the magnitude range +3 to −1, corresponding to meteoroid sizes 1-10 mm. For the majority of the meteors, heliocentric orbits are known as well. We classified the spectra according to relative intensities of the lines of Mg, Na, and Fe. Theoretical intensities of these lines for a chondritic composition of the meteoroid and a wide range of excitation and ionization conditions were computed. We found that only a minority of the meteoroids show chondritic composition. Three distinct populations of Na-free meteoroids, each comprising ∼10% of sporadic meteoroids in the studied size range, were identified. The first population are meteoroids on asteroidal orbits containing only Fe lines in their spectra and possibly related to iron-nickel meteorites. The second population are meteoroids on orbits with small perihelia (q?0.2 AU), where Na was lost by thermal desorption. The third population of Na-free meteoroids resides on Halley type cometary orbits. This material was possibly formed by irradiation of cometary surfaces by cosmic rays in the Oort cloud. The composition of meteoroids on Halley type orbits is diverse, probably reflecting internal inhomogeneity of comets. On average, cometary dust has lower than chondritic Fe/Mg ratio. Surprisingly, iron meteoroids prevail among millimeter-sized meteoroids on typical Apollo-asteroid orbits. We have also found varying content of Na in the members of the Geminid meteoroid stream, suggesting that Geminid meteoroids were not released from their parent body at the same time.     

Condensed species in Titan's atmosphere: Identification of crystalline propionitrile (C2H5CN, CH3CH2CN) based on laboratory infrared data

We report the results of infrared studies of crystalline C₂H₅CN at several temperatures between 15 and 160 K. A case is made for the identification of crystalline C₂H₅CN in the stratosphere from the Voyager IRIS spectrum of Titan.     

A sensitive search for SO2 in the martian atmosphere: Implications for seepage and origin of methane

Mars was observed near the peak of the strongest SO₂ band at 1364-1373 cm⁻¹ with resolving power of 77,000 using the Texas Echelon Cross Echelle Spectrograph on the NASA Infrared Telescope Facility. The observation covered the Tharsis volcano region which may be preferable to search for SO₂. The spectrum shows absorption lines of three CO₂ isotopomers and three H₂O isotopomers. The water vapor abundance derived from the HDO lines assuming D/H = 5.5 times the terrestrial value is 12±1.0 pr. μm, in agreement with the simultaneous MGS/TES observations of 14 pr. μm at the latitudes (50° S to 10° N) of our observation. Summing of spectral intervals at the expected positions of sixteen SO₂ lines puts a 2σ upper limit on SO₂ of 1 ppb. SO₂ may be emitted into the martian atmosphere by seepage and is removed by three-body reactions with OH and O. The SO₂ lifetime, 2 years, is longer than the global mixing time 0.5 year, so SO₂ should be rather uniformly distributed across Mars. Seepage of SO₂ is less than 15,000 tons per year on Mars which is smaller than the volcanic production of SO₂ on the Earth by a factor of 700. Because CH₄/SO₂ is typically 10⁻⁴-10⁻³ in volcanic gases on the Earth, our results show seepage is unlikely to be the source of the recently discovered methane on Mars and therefore strengthen its biogenic origin.     

Coordination of water molecules with Na+ cations in a beryl channel as determined by polarized IR spectroscopy

Subtle variations of frequencies in the infrared (IR) absorption spectra of beryl have been predicted based on the coordination between extra-framework cations and water molecules in two orientations (referred to as type I and type II) trapped within the channel. In this study, the polarized IR spectra of hydrated synthetic beryl and natural beryl were measured to clarify the relationships between the frequencies of the absorption bands and the coordination states of type II water. Na⁺ was assumed to be the predominant cation coordinated to type II water in our samples, as determined by chemical analyses. These measurements revealed a clear quantitative linear relationship in absorbance between bands at 3,602 and 1,619 and at 3,589 and 1,631 cm⁻¹. On the basis of experimental and theoretical studies, we assigned these pairs of bands to the ν₁ and ν₂ modes of doubly coordinated type II H₂O and to singly coordinated type II H₂O, respectively. These assignments were supported by IR measurements of annealed natural beryl. We also conducted dehydration studies of natural beryl, in which two observed dehydration peaks, at 600 and 750°C, suggested the dehydration of type I and type II water, respectively.     

Extrinsic and intrinsic mode of hydrogen occurrence in natural olivines: FTIR and TEM investigation

Olivine crystals from two mantle nodules in kimberlites (pipe Udachnaya and pipe Obnazennaya, Yakutiya, Siberia) were investigated using EMP, TEM, AEM and FTIR techniques to determine the mode of hydrogen occurrence in olivine. Olivine contains three types of nanometer-sized inclusions: “large” inclusions of hexagonal-like shape up to several hundred nm in size (1), lamellar defects (2) and small inclusions of hexagon-like shape up to several 10?nm in size (3). Lamellar defects and small inclusions are considered to be a “hydrous” olivine. All three types of inclusions contain OH^? or water, but they are different with respect to their phase composition. In “large” inclusions (1) hydrous magnesium silicates, such as serpentine?+?talc (“kerolite”?) and 10-Å phase?+?talc were identified. Lamellar defects (2) and small inclusions (3) are depleted in Mg and Fe compared to the olivine matrix, while the silica content is the same as that of olivine. Modulations in the periodicity of the olivine structure are observed in SAED patterns and HREM images of (2) and (3). The superperiodicity can be referred to OH^?-bearing point defect ordering in the olivine structure. If this is the case, the material of both lamellar defects and small inclusions can be assumed to be a “hydrous olivine” Mg_{2– x} v _x SiO₄H_{2 x} with a cation-deficient olivine crystal structure. Thus, both an extrinsic mode of hydrogen occurrence in olivine, such as nanometer-sized inclusions of OH^?-bearing magnesium silicates, and an intrinsic mode of hydrogen incorporation into the olivine structure, such as “hydrous olivine” in itself, were found. The data obtained here show that the OH absorption bands observed in olivine spectra at 3704(3717) and 3683(3688) cm^?1 can be unambiguously identified with serpentine; the band at 3677(3676) cm^?1 can be associated with talc. The absorption bands observed at 3591 and 3660?cm^?1 in olivine match those of the 10-Å phase at 3594, 3662 and 3666?cm^?1.     

Ionizing radiation-induced defects in smectite clays

 The interaction of γ-rays with smectites induces paramagnetic defects in the structure of these clay minerals. The EPR spectra of three different smectites detect the creation of structural defects and trapping of organic free radicals in the clay structure upon irradiation. The defects are assigned to positive holes or trapped electrons stabilised by existing local charge imbalances in the mineral lattice. The organic radicals are derived from organic compounds present as impurities in the crystal lattice of the clay minerals. In addition, γ-rays cause migration of small interlayer cations (such as Li⁺) into the layers, as clearly evidenced by EPR and FT-IR reflectance spectroscopies. Received: 20 April 2000 / Accepted: 2 December 2000     

西太平洋热带海域的水汽和云的变化特性

本文依据1987年9—11月西太平洋热带海域海洋大气综合考察中双波长微波辐射计观测系统和红外窗区辐射计所得到的观测资料,分析研究了考察海域的水汽和云的变化特性,得到了一些有意义的结果。双波长微波辐射计观测系统可以获得水汽场的动态变化和云中液态水的演变;西太平洋海域的个例显示出辐合区的垂直气柱水汽含量比非辐合区的明显大的特征;用红外亮度温度可以近似估计晴空大气垂直气柱水汽含量。     

Observations and modeling of infrared and millimeter molecular lines towards GL2591

We have observed C₂H₂ and HCN rovibrational transitions near 13µm in absorption against GL2591. We also have observed rotational transitions at 0.6-3 mm of CS, HCN, H₂CO, and HCO⁺. Analysis of the rotational lines, which arise in the extended cloud around the source, shows that no single density model can explain all the data. Models with density and temperature gradients do much better; in particular models withn(r) r ^–1.5 can reproduce the observed pattern of emission line strengths. The abundances show significant depletion compared to models of gas-phase chemistry. The rovibrational data were analyzed in comparison to the absorption line analysis of CO by Mitchellet al. (1989). Our data are consistent with the C₂H₂ and HCN absorption arising in the same warm (200 K) and hot (1010 K) components seen in CO, but we see little evidence for the cold (38 K) component seen in CO. The rovibrational lines from higher states (J 21) indicate that the hot HCN deviates from LTE, leading to a density of about 3 × 10⁷ cm^–3. Comparison of the two data sets shows that the rovibrational absorption of HCN, rather than arising in the extended envelope, must come from a region with a small angular extent. A model in which early-time gas phase abundances are preserved on grain mantles and released at high temperature can explain the data.     

无色-近无色高温高压合成钻石的谱图特征及其鉴别方法

实验室发现大量小颗粒的无色高温高压(HPHT)合成钻石与天然钻石混杂镶嵌在各种饰品中,前人提出荧光和磷光特征是主要的快速区分特征,然而荧光、磷光特征的差异并不能完全将HPHT合成钻石与天然钻石区分开来。本文将常规的宝石学观察分析与多种高精度谱学测试相结合,对五粒不同的无色-近无色HPHT合成钻石样品进行深入研究。结果表明,五粒钻石在紫外可见吸收光谱无270 nm吸收或是只有极弱的270 nm吸收,随着颜色级别的降低,270 nm吸收越明显。红外光谱测试显示,各粒样品中都含有不等量的硼元素。光致发光光谱测试表明,HPHT合成钻石含有与微量N、Ni、Si等相关的晶格缺陷。超短波紫外光源激发下,所有的HPHT合成钻石都有强磷光,在钻石观察仪下可以观测到清晰的八面体和立方体分区特征。显然,不同的合成钻石的特征略有差异,但综合其荧光及磷光特征以及红外、紫外、光致发光光谱特征,可以准确地将无色HPHT合成钻石与对应的天然钻石区分开来。     

A new hypothesis about the surface circulation in the eastern basin of the mediterranean sea

In time, the circulation of the Atlantic Water (AW) in the eastern basin of the Mediterranean Sea has been described differently, according to two major representations. The historical one, which began with the scheme from Nielsen in 1912 and has been refined up to the 1980s, favours a counterclockwise circulation in the whole basin, with AW flowing in its southern part as a broad flow off Libya and Egypt (from the Ionian to the Levantine subbasins), then continuing along Middle-East and Turkey before flowing back westwards. The more recent one, issued in the 1990s, favours a clockwise circulation in the northern part of the Ionian continuing offshore across the basin from the Cretan to the central part of the Levantine as the so-called “Mid-Mediterranean Jet”. This jet is depicted then as splitting both clockwise in the southeastern part of the basin and counterclockwise off Turkey (where this representation agrees with the former). Because the recent representation cannot be considered as a refinement of the historical ones, we have been interested in understanding why a given data set available to everybody is interpreted in such different ways.In the Algerian subbasin, the combined use of satellite infrared images and a significant amount of in situ data sets (hydrology and both Eulerian and Lagrangian current measurements) allowed us to solve a similar controversy. Therefore, we examined the circulation features in the eastern basin, undertaking the detailed analysis of 1000 daily and weekly composite images spanning the period 1996–2000, and of monthly composite images available since 1985. Whenever in situ observations were available, we have confronted them with the satellite thermal signatures and have shown that both are consistent. This paper focuses on the overall (basin scale) results while the detailed ones are published in an other paper. The new scheme we propose is basically a refined version of the historical ones: the circulation of AW is counterclockwise in the whole eastern basin but it is more constrained alongslope than previously thought, and the broadening historically schematised appears to be due to intense mesoscale eddies mainly generated by the instability of this circulation.