Radio OH observations of 9P/Tempel 1 before and after Deep Impact   总被引：1，自引：0，他引：1  

Ellen S. Howell  Amy J. Lovell  F. Peter Schloerb 《Icarus》2007,187(1):228-239

We observed 18-cm OH emission in Comet 9P/Tempel 1 before and after Deep Impact. Observations using the Arecibo Observatory 305 m telescope took place between 8 April and 9 June, 2005, followed by post-impact observations using the National Radio Astronomy Observatory 100 m Green Bank Telescope 4-12 July, 2005. The resulting spectra were analyzed with a kinematic Monte Carlo model which allows estimation of the OH production rate, neutral gas outflow velocity, and distribution of the out-gassing from the nucleus. We detected typically 24% variability from the overall OH production rate trend in the two months leading up to the impact, and no dramatic increase in OH production in the days post-impact. Generally, the coma is well-described, within uncertainties, by a symmetric model with OH production rates from 1.6 to , and mean water outflow velocity of . At these low production rates, collisional quenching is expected to occur only within 20,000 km of the nucleus. However, our best-fit average quenching radius is 64,200 ± 22,000 km in April and May.  相似文献   

Radio observations of Comet 9P/Tempel 1 before and after Deep Impact     

Nicolas Biver  Dominique Bockelée-Morvan  Jacques Crovisier  Alain Lecacheux  Gabriel Paubert  Matthew Sumner  Åke Hjalmarson  Anders Winnberg  Aage Sandqvist 《Icarus》2007,187(1):253-271

Comet 9P/Tempel 1 was the target of a multi-wavelength worldwide investigation in 2005. The NASA Deep Impact mission reached the comet on 4.24 July 2005, delivering a 370-kg impactor which hit the comet at 10.3 km s⁻¹. Following this impact, a cloud of gas and dust was excavated from the comet nucleus. The comet was observed in 2005 prior to and after the impact, at 18-cm wavelength with the Nançay radio telescope, in the millimeter range with the IRAM and CSO radio telescopes, and at 557 GHz with the Odin satellite. OH observations at Nançay provided a 4-month monitoring of the outgassing of the comet from March to June, followed by the observation of H₂O with Odin from June to August 2005. The peak of outgassing was found to be around between May and July. Observations conducted with the IRAM 30-m radio telescope in May and July 2005 resulted in detections of HCN, CH₃OH and H₂S with classical abundances relative to water (0.12, 2.7 and 0.5%, respectively). In addition, a variation of the HCN production rate with a period of 1.73±0.10 days was observed in May 2005, consistent with the 1.7-day rotation period of the nucleus. The phase of these variations, as well as those of CN seen in July by Jehin et al. [Jehin, E., Manfroid, J., Hutsemékers, D., Cochran, A.L., Arpigny, C., Jackson, W.M., Rauer, H., Schulz, R., Zucconi, J.-M., 2006. Astrophys. J. 641, L145-L148], is consistent with a rotation period of the nucleus of 1.715 days and a strong variation of the outgassing activity by a factor 3 from minimum to maximum. This also implies that the impact took place on the rising phase of the “natural” outgassing which reached its maximum ≈4 h after the impact. Post-impact observations at IRAM and CSO did not reveal a significant change of the outgassing rates and relative abundances, with the exception of CH₃OH which may have been more abundant by up to one order of magnitude in the ejecta. Most other variations are linked to the intrinsic variability of the comet. The Odin satellite monitored nearly continuously the H₂O line at 557 GHz during the 38 h following the impact on the 4th of July, in addition to weekly monitoring. Once the periodic variations related to the nucleus rotation are removed, a small increase of outgassing related to the impact is present, which corresponds to the release of ≈5000±2000 tons of water. Two other bursts of activity, also observed at other wavelengths, were seen on 23 June and 7 July; they correspond to even larger releases of gas.  相似文献   

Palomar and Table Mountain observations of 9P/Tempel 1 during the Deep Impact encounter: First results     

James M. Bauer  Paul R. Weissman  Mitchell Troy  Carey M. Lisse  Martha S. Hanner 《Icarus》2007,187(1):296-305

We present the first results of the Palomar Adaptive Optics observations taken during the Deep Impact encounter with 9P/Tempel 1 in July 2005. We have combined the Palomar near-IR imaging data with our visual wavelength images obtained simultaneously at JPL's Table Mountain Observatory to cover the total wavelength range from 0.4 to 2.3 μm in the B, V, R, I, J, H, and K filter bands, spanning the dates from 2005 July 03-07. We also include in our overall analysis images taken on the pre-encounter dates of June 1 and June 15, 2005. The broad wavelength range of our observations, along with high temporal resolution, near-IR sensitivity, and spatial resolution of our imaging, have enabled us to place constraints on the temperature of the impact flash and incandescent plume of >700 K, and to provide mean dust velocities of order approximately 1.25 h after impact derived from our 1.64 μm observations. Our ejected dust mass estimates, as derived from our near-IR observations, are an order of magnitude less than those previously reported for visual wavelength observations.  相似文献   

近期乌鲁木齐河源1号冰川成冰带及雪层剖面特征研究   总被引：14，自引：9，他引：5  

李向应  李忠勤  尤晓妮  王飞腾  李传金  朱宇曼 《冰川冻土》2006,28(1):37-44

天山乌鲁木齐河源1号冰川的成冰带20世纪60年代初,自下而上划分为4个成冰带;1988年,由于气候变暖,冰川上部的冷渗浸重结晶带消失,被渗浸带所取代.对近期1号冰川的成冰带进行了划分,并通过大量雪坑资料,研究论述了目前1号冰川雪层剖面的层位特征.研究发现,由于气候变暖,剖面特征和成冰带谱有由“冷”向“暖”的转化趋势.同时还发现,1号冰川东支顶部发生了强烈的消融现象,该处已由渗浸带转化为具有强烈消融特征的局部消融区.  相似文献   

Submillimeter Wave Astronomy Satellite observations of Comet 9P/Tempel 1 and Deep Impact     

Frank Bensch  Gary J. Melnick  Martin Harwit  Ronald L. Snell  Volker Tolls 《Icarus》2006,184(2):602-610

On 4 July 2005 at 5:52 UT the Deep Impact mission successfully completed its goal to hit the nucleus of 9P/Tempel 1 with an impactor, forming a crater on the nucleus and ejecting material into the coma of the comet. NASA's Submillimeter Wave Astronomy Satellite (SWAS) observed the ₁₁₀-₁₀₁ ortho-water ground-state rotational transition in Comet 9P/Tempel 1 before, during, and after the impact. No excess emission from the impact was detected by SWAS and we derive an upper limit of 1.8×¹⁰⁷ kg on the water ice evaporated by the impact. However, the water production rate of the comet showed large natural variations of more than a factor of three during the weeks before and after the impact. Episodes of increased activity with alternated with periods with low outgassing (). We estimate that 9P/Tempel 1 vaporized a total of N∼4.5×¹⁰³⁴ water molecules (∼1.3×¹⁰⁹ kg) during June-September 2005. Our observations indicate that only a small fraction of the nucleus of Tempel 1 appears to be covered with active areas. Water vapor is expected to emanate predominantly from topographic features periodically facing the Sun as the comet rotates. We calculate that appreciable asymmetries of these features could lead to a spin-down or spin-up of the nucleus at observable rates.  相似文献   

Perihelion motion of small irregular dust particles due to radiation forces     

J. Kla?ka  F. Kundracík 《Planetary and Space Science》2006,54(4):379-393

Perihelion motion, i.e. a secular change of longitude of perihelion, of interplanetary dust particles is investigated under the action of solar gravity and solar electromagnetic radiation. As for spherical particle [Kla?ka, J., 2004. Electromagnetic radiation and motion of a particle. Cel. Mech. Dynam. Astron. 89, 1-61]: (i) perihelion motion is of the order ( is heliocentric velocity of the meteoroid and c is the speed of light in vacuum), if a component of electromagnetic radiation acceleration is considered as a part of central acceleration; (ii) perihelion motion is of the first order in if the total electromagnetic radiation force is considered as a disturbing force. The new facts presented in this paper concern irregular dust particles. Detailed numerical calculations were performed for the grains ejected at aphelion of comet Encke. Perihelion motion for irregular interplanetary dust particles exists already in the first order in for both cases of central accelerations. Moreover, perihelion motion of irregular particles exhibits both positive and negative directions during the particle orbital motion. Irregularity of the grains causes not only perihelion motion, but also dispersion of the dust in various directions, also normal to the orbital plane of the parent body.  相似文献   

1：10000地形图航摄成图内业质量控制方法研究     

李津岭  张道明  赵淑玲 《东北测绘》2012,(8):211-213

介绍了1∶10 000地形图航摄成图内业生产质量控制的方法,并以实际工作为依据,对该方法进行了详细阐述。同时,还介绍了元数据的生产和质量自动控制方法。  相似文献   

基于动态阈值的HJ-1B图像云检测算法研究     

韩杰  杨磊库  李慧芳  梁洪有  马晓红  谢玉娟 《国土资源遥感》2012,(2):12-18

针对环境与灾害监测预报小卫星星座1B星(HJ-1B)的传感器波段特征,通过对云检测阈值的年度波动性分析,提出了一种基于波谱标准差异常的“动态阈值云检测算法”.该算法的实现主要是采用图像配准、波段运算、线性回归和误差分析等方法,获取云异常区域,进而剔除图像中的云像元.研究结果表明,该算法可以很好地检测出不同时相、不同类型下垫面上空的云像元,为有效利用HJ-1B数据并提高其图像分类精度发挥作用.  相似文献   

1：50000数据库的更新服务数据库系统设计与实现     

张元杰  商瑶玲  段松鹤  查祝华 《测绘软科学研究》2012,(1):27-31

1：50000数据库的更新工程数据库服务系统是以1：50000数据库更新成果为基础．建立了一个基于B／S结构的服务系统,满足更新数据快速发布、浏览、应急服务等需求。本文介绍了陔系统的设计思想、系统总体架构、数据库设计与建库、软件功能设计与实现,为其他地理信息数据系统建设提供借豁。  相似文献   

基于GIS交通网络的室内3维网络模型研究     

徐效波  吴华玲  郭先春  罗艳 《测绘软科学研究》2012,(2):61-64

在2维交通网络逻辑数据模型基础上,讨论了概念化的楼层网络,进行了室内连通的3维网络模型的研究。基于ArcGIS的交通网络模型建立了试验区的室内3维网络模型．并给出分析结果,该方法为室内3维网络模型研究提供了技术支持。  相似文献