Dark red debris from three short-period comets: 2P/Encke, 22P/Kopff, and 65P/Gunn

We present observations of the extended dust structures near the orbits of three short-period comets: 2P/Encke, 22P/Kopff, and 65P/Gunn. The dust trails were originally discovered by the Infrared Astronomical Satellite (IRAS). Our observations were made using wide-field optical CCD cameras on the University of Hawaii 2.24-m telescope, the Canada-France-Hawaii 3.6-m telescope, and the Kiso 1.05-m Schmidt telescope. We compared the observed images with models and found that the extended structures seen around 2P/Encke and 22P/Kopff before perihelion passage were most likely “dust trails,” whereas images taken after perihelion passage show a high contamination by recently released particles (i.e., particles in Neck-Line structures are visible). We could not confirm the existence of a dust trail from 65P/Gunn within the field of view of the camera used. The effective sizes of the particles responsible for the scattered light were estimated at 1-100 mm (2P/Encke), 1-10 mm (22P/Kopff), and 100 μm-1 mm (65P/Gunn), respectively, which is consistent with previous studies of dust trails made with infrared space telescopes and optical telescopes. We evaluated the mass loss rates of these comets, averaged over their orbits, as reaching (2P/Encke), (22P/Kopff), and (65P/Gunn). These values are consistent with previous work. Therefore, the total amount of material ejected from these three comets is , which would contribute a considerable fraction of the lost within 1 AU that needs to be replaced if the zodiacal cloud is to be maintained in a steady state. We also found that the particles in the dust structures are significantly redder than the Sun and the zodiacal light, and might be redder than the average short-period comet nuclei. Specifically, the reflectivity gradients of 2P/Encke, 22P/Kopff, and 65P/Gunn are 13±7 (% ¹⁰³ Å⁻¹), 20±5 (% ¹⁰³ Å⁻¹), and 15±4 (% ¹⁰³ Å⁻¹), respectively. We examined the change in color with distance from the nucleus. No clear correlation was detected for 2P/Encke or 22P/Kopff to an accuracy of 3-11%, while the 65P/Gunn tail did show color variation, becoming redder with increasing distance from the nucleus. This dark red material, consisting of particles of sand-cobble size, has marginally escaped from the nuclei and will evolve into finer-grained interplanetary dust particles after subsequent collisions.     

湖泊沉积物中磷形态标准物质研制

水体富营养化与沉积物中磷元素的形态有密切关系。为了准确测定沉积物中不同形态的磷的含量,欧盟在2000年研制了第一个湖泊沉积物中磷形态标准物质(BCR 684),但基本用尽已不能满足需求,而且该标准物质采集于欧洲某湖泊,沉积物类型及污染情况与我国湖泊不相匹配。本文结合我国沉积物的类型和湖泊污染状况,研制了我国首批2个湖泊沉积物中磷形态标准物质(编号为 GBW 07462和GBW 07463)。候选物样品采集地点为江苏太湖和湖南洞庭湖,样品经过自然干燥、研磨、灭菌、陈化等加工处理,随机抽取15个子样采用单因素方差分析(F检验法)进行均匀性检验,检验的F实测值均小于临界值,表明样品均匀性良好。根据ISO导则35推荐方法对候选物样品在一年内进行四次稳定性检查,分析结果无方向性变化,再通过2次验证实验,样品稳定性良好。此批磷形态标准物质采用8家实验室联合定值,定值参数包括五种磷形态:总磷、无机磷、有机磷、磷灰石态磷、非磷灰石态磷;磷形态提取方法采用欧盟SMT法,测定方法采用钼锑钪光度法和电感耦合等离子体发射光谱法(实验过程中用欧盟BCR 684作为质量监控);按照《一级标准物质研制规范》(JJG 1006—1994)和ISO导则35的要求给出了五种磷形态的标准值和不确定度。此批磷形态标准物质样品代表了我国典型富营养化湖泊的沉积物类型,采样点的区域代表性强,定值项目选择合理、量值准确,可应用于环境、地质、农业、地球化学等研究领域沉积物的磷形态样品质量监控。     

Mafic silicate mapping on Mars: effects of palagonitic material, multiple mafic silicates, and spectral resolution

The visible to near-infrared spectral reflectance properties of intimate and areal pyroxene?+?palagonitic material mixtures as well as pure mafic silicates (low-calcium pyroxene, high-calcium pyroxene, pigeonite, olivine) and mixtures of these minerals were analyzed at high spectral resolution (5 nm) as well as with non-contiguous band passes equivalent to recent HST observations and the Pathfinder IMP in order to determine the quality and quantity of mineralogical information (end member compositions, abundances, and grain sizes) derivable in the presence of palagonitic material. In the case of pyroxene?+?palagonitic material mixtures, pyroxene is detectable at abundances as low as 10 wt%, and its composition can be constrained because (a) its diagnostic absorption feature (located near 1000 nm) persists even for high palagonitic material abundances, and (b) palagonitic material does not appreciably alter the wavelength position of this band (<4 nm variation). For broad band data (such as Pathfinder IMP band passes), different mafic silicates can be discriminated and palagonitic material abundances constrained using a variety of reflectance ratios and three-point “absorption band depths.” However, other properties of mafic silicate?±?palagonitic material assemblages, such as mafic silicate major element compositions, grain sizes, and end member abundances, generally cannot be rigorously quantified. The use of multiple reflectance ratios can, however, be used to identify relative changes in these properties, as most changes in mafic silicate?±?palagonitic material assemblage properties are characterized by a unique corresponding set of reflectance ratio variations. The observed spectral-assemblage property trends are consistent with those expected from the known spectral properties of the end members.     

Physical characterization of the potentially hazardous high-albedo Asteroid (33342) 1998 WT24 from thermal-infrared observations

The potentially hazardous Asteroid (33342) 1998 WT₂₄ approached the Earth within 0.0125 AU on 2001 December 16 and was the target of a number of optical, infrared, and radar observing campaigns. Interest in 1998 WT₂₄ stems from its having an orbit with an unusually low perihelion distance, which causes it to cross the orbits of the Earth, Venus, and Mercury, and its possibly being a member of the E spectral class, which is rare amongst near-Earth asteroids (NEAs). We present the results of extensive thermal-infrared observations of 1998 WT₂₄ obtained in December 2001 with the 3-m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii and the ESO 3.6-m telescope in Chile. A number of thermal models have been applied to the data, including thermophysical models that give best-fit values of 0.35±0.04 km for the effective diameter, 0.56±0.2 for the geometric albedo, pv, and 100-300 J m⁻² s^−0.5 K⁻¹ for the thermal inertia. Our values for the diameter and albedo are consistent with results derived from radar and polarimetric observations. The albedo is one of the highest values obtained for any asteroid and, since no other taxonomic type is associated with albedos above 0.5, supports the suggested rare E-type classification for 1998 WT₂₄. The thermal inertia is an order of magnitude higher than values derived for large main-belt asteroids but consistent with the relatively high values found for other near-Earth asteroids. A crude pole solution inferred from a combination of our observations and published radar results is β=−52°, λ=355° (J2000), but we caution that this is uncertain by several tens of degrees.     

Young Asteroid 832 Karin shows no rotational spectral variations

We have made near-IR spectral observations of the very young (5.75 Myr) S-type asteroid 832 Karin, well sampled in rotational phase over its 18.35-h period. We find no significant variations in its reflectance spectrum. Karin, the brightest member of the Karin cluster (a sub-family of the larger, older Koronis dynamical family), was shown to be exceptionally young by Nesvorný et al. [Nesvorný, D., Bottke, W.F., Dones, L., Levison, H., 2002. Nature 417, 720-722], using backward numerical integration of orbital elements of cluster members. Their precise dating of the collisional breakup gives us an opportunity, for the first time and without age-dating of physical samples, to monitor time-evolution of processes, like space weathering, that operate on timescales of ∼1-10 Myr. Sasaki et al. [Sasaki, T., Sasaki, S., Watanabe, J., Sekiguchi, T., Yoshida, F., Kawakita, H., Fuse, T., Takato, N., Dermawan, B., Ito, T., 2004. Astrophys. J. 615, L161-L164; Sasaki, T., Sasaki, S., Watanabe, J., Sekiguchi, T., Yoshida, F., Ito., T., Kawakita, H., Fuse, T., Takato, N., Dermawan, B., 2005. Lunar Planet. Sci. XXXVI. Abstract #1590] had made similar measurements of Karin, although more sparsely sampled than ours, and claimed dramatically different colors as a function of rotational phase. Sasaki et al. interpreted their data to be showing the reddish, space-weathered exterior surface of the precursor asteroid, as well as an interior face, which had not had time to become space-weathered. On five nights over 2006 January 7-14 UT, we observed Karin with the SpeX (0.8-2.5 μm) spectrometer of the IRTF. We analyze data in 30° intervals of rotational longitude, some of which we sampled on two different nights. The spectra are consistent with little or no spectral variation as the asteroid rotates; certainly there are no changes as large as previously reported. The previous observations were probably spurious. Our average spectrum resembles the “blue” spectrum of Sasaki et al., which they interpreted to be the “fresh” surface. Karin is not quite as red as typical S-types, yet has rather shallow absorption bands. We surmise that the space-weathering process affecting Karin has had time to reduce spectral contrast, but has not operated long enough to redden its spectrum—an intermediate case of space weathering, which has gone to completion for most main-belt asteroids. This work sets an important constraint on the timescale for the ubiquitous space-weathering process affecting S-types, namely that its effects are evident, but not yet complete, at ∼6 Myr.     

Asteroid observations at low phase angles: III. Brightness behavior of dark asteroids

The results of photometric observations of eight main-belt asteroids with low surface albedo are presented. The magnitude-phase dependences including low phase angles (<1 deg) have been obtained for Asteroids 76 Freia (down to phase angle 0.1 deg, P-type), 190 Ismene (0.3 deg, P-type), 303 Josephina (0.2 deg, C-type), 309 Fraternitas (0.1 deg, C-type), 313 Chaldaea (0.1 deg, C-type), 444 Gyptis (0.8 deg, P-type), 615 Roswitha (0.1 deg, C-type), and 954 Li (0.03 deg, FCX-type). The behavior of brightness in the range of opposition effect is found to be practically linear for 190 Ismene with amplitude of opposition effect only 0.03 mag. Amplitudes of the opposition effect for other asteroids are close to a mean for this type. The obtained data allowed us also to determine the rotation periods of asteroids: 303 Josephina (12.497±0.001 h), 309 Fraternitas (11.205±0.005 h), 615 Roswitha (4.422±0.001 h) and 954 Li (7.207±0.002 h). The color indexes B-V, V-R and R-I have been determined for some asteroids.     

Optical and thermal infrared observations of six near-Earth asteroids in 2002

We present thermal infrared photometry and spectrophotometry of six Near-Earth Asteroids (NEAs) using the 3.8 m United Kingdom Infrared Telescope (UKIRT) together with quasi-simultaneous optical observations of five NEAs taken at the 1.0 m Jacobus Kapteyn Telescope (JKT). For Asteroid (6455) 1992 HE we derive a rotational period P=2.736±0.002 h, and an absolute visual magnitude H=14.32±0.24. For Asteroid 2002 HK₁₂ we derive . The Standard Thermal Model (STM), the Fast Rotating Model (FRM) and the Near-Earth Asteroid Thermal Model (NEATM) have been fitted to the measured fluxes to derive albedos and effective diameters. The derived geometric albedos and effective diameters are (6455) 1992 HE: pv=0.26±0.08, Deff=3.55±0.5 km; 1999 HF₁: pv=0.18±0.07, ; 2000 ED₁₀₄: pv=0.18±0.05, Deff=1.21±0.2 km; 2002 HK₁₂: , Deff=0.62±0.2 km; 2002 NX₁₈: pv=0.031±0.009, Deff=2.24±0.3 km; 2002 QE₁₅: , Deff=1.94±0.4 km. The limitations of using the NEATM to observe NEAs at high phase angles are discussed.     

钌的硫脲比色测定

本文讨论了钌同硫脲的显色反应，在不经分离的条件下，将Ｒｕ还原Ｒｕ￣Ⅱ，Ｒｕ￣Ⅱ与硫脲生成蓝色，λ＿最大＝６３５ｎｍ，在０－３００μｇ／ｍｌ范围内呈线性关系。本法适宜测定含Ｒｕ量较高钌的渣及其选矿成品。     

Determination of dissolved organic matter in streamwater using visible spectrophotometry: A comment

A discussion querying the need (Grieve, 1985) for further studies on the use of the technique, which is already well established. The use of chemical oxygen demand is also questioned.     

A simplified resorcinol method for direct spectrophotometric determination of nitrate in seawater

A direct, spectrophotometric method has been adapted for quantitative determination of nitrate concentrations in seawater. The method is based on nitration of resorcinol in acidified seawater, resulting in a color product. The absorption spectrum obtained for the reaction product shows a maximum absorption at 505 nm, with a molar absorptivity of 1.7 × 10⁴ L mol^− 1 cm^− 1. This method has a detection limit of 0.5 μM and is linear up to 400 μM for nitrate. The advantage of this method is that all reagents are in aqueous solutions without involving cadmium granules as a heterogeneous reactant, as in conventional methods, and therefore is simple to implement. Application of the resorcinol to seawater analysis demonstrated that the results obtained are in good agreement with the conventional approach involving the reduction of nitrate by cadmium followed by diazotization.