The PRIMA facility phase-referenced imaging and micro-arcsecond astrometry     

Franoise Delplancke 《New Astronomy Reviews》2008,52(2-5):199

This article describes dual-field interferometry, in particular PRIMA, the phase-referenced imaging and micro-arcsecond astrometry facility of the very large telescope interferometer. It uses the simultaneous detection of fringes of two stars in a narrow angle and the accurate measurement of their respective positions. PRIMA aim is threefold: (i) to increase the VLTI limiting magnitude with off-axis fringe tracking, (ii) to reconstruct images with a resolution of 2 mas in K-band, 10 mas in N-band, and (iii) to perform differential narrow-angle astrometry with an accuracy of 10 μas. This article exposes the fundamental and technical limitations of such a technique and presents how PRIMA will try to solve the practical problems of measuring 100-m long optical paths with nanometric accuracy in a ground based interferometer.  相似文献   

A massive, dusty toroid with large grains in the pre-planetary nebula IRAS22036+5306     

R. Sahai  K. Young  N. Patel  C. Sánchez Contreras  M. Morris 《Astrophysics and Space Science》2008,313(1-3):241-244

Using the Submillimeter Array (SMA), we have obtained high angular-resolution (∼1″) interferometric maps of the submillimeter (0.88 mm) continuum and CO J=3–2 line from IRAS 22036+5306 (I 22036), a bipolar pre-planetary nebula (PPN) with knotty jets discovered in our HST SNAPshot survey of young PPNe. In addition, we have obtained supporting lower-resolution (∼10″) 2.6 mm continuum and CO, ¹³CO J=1–0 observations with the Owens Valley Radio Observatory (OVRO) interferometer. We find an unresolved source of submillimeter (and millimeter-wave) continuum emission in I 22036, implying a very substantial mass (0.02–0.04M _⊙) of large (i.e., radius ≳1 mm), cold (≲50 K) dust grains associated with I 22036’s toroidal waist. The CO J=3–2 observations show the presence of a very fast (∼220 km s⁻¹), highly collimated, massive (0.03M _⊙) bipolar outflow with a very large scalar momentum (about 10³⁹ g cm s⁻¹), and the characteristic spatio-kinematic structure of bow-shocks at the tips of this outflow. The fast outflow in I 22036, as in most PPNe, cannot be driven by radiation pressure. The large mass of the torus suggests that it has most likely resulted from common-envelope evolution in a binary, however it remains to be seen whether or not the time-scales required for the growth of grains to millimeter sizes in the torus are commensurate with such a formation scenario. The presence of the torus should facilitate the formation of the accretion disk needed to launch the jet. We also find that the ¹³C/¹²C ratio in I 22036 is very high (0.16), close to the maximum value achieved in equilibrium CNO-nucleosynthesis (0.33). The combination of the high circumstellar mass (i.e., in the torus and an extended dust shell inferred from ISO far-infrared spectra) and the high ¹³C/¹²C ratio in I 22036 provides strong support for this object having evolved from a massive (≳4M _⊙) progenitor in which hot-bottom-burning has occurred.  相似文献   

Cometary science with ALMA     

Dominique Bockelée-Morvan 《Astrophysics and Space Science》2008,313(1-3):183-189

This paper presents a prospect for the observations of comets with ALMA. Thanks to unprecedented sensitivity, angular resolution and instantaneous uv-coverage, key measurements on a number of topics related to the chemical and physical properties of the coma and the nucleus will be obtained. These include (1) the identification of new molecular species and measurements of key isotopic ratios, (2) measurements of the composition of short-period comets coming from the trans-Neptunian scattered disc, to investigate chemical diversity within the whole comet population, (3) imaging of gas jets and their relationship with dust features, (4) the study of extended sources of gas in the coma, and (5) the study of the physical and outgassing properties of the nucleus.  相似文献   

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杨久东  田辉  周春霞 《大地测量与地球动力学》2010,30(1):9-13

????DORIS?????????????ENVISAT????????????NASA??????SRTM?????????DEM????????????????????????????????????α??????????????????????????????????????????????????ε??????????????????????????????????????????????????????25.2 cm??  相似文献   

利用空间技术求解现时板块运动参数   总被引：1，自引：0，他引：1  

毛悦  孙付平 《四川测绘》2005,28(1):3-6

本文综合利用GPS及VLBI技术，以站心坐标速度为观测量，求解了五个主要板块的绝对和相对板块运动参数，进行了精度分析。并与传统的NUIVEL-1 A地学板块运动模型进行了比较，在一定程度上说明全球板块运动在最近300万年内总体上趋于稳定。  相似文献   

Comparisons of homogeneously reprocessed GPS and VLBI long time-series of troposphere zenith delays and gradients     

Peter Steigenberger  Volker Tesmer  Manuela Krügel  Daniela Thaller  Ralf Schmid  Sibylle Vey  Markus Rothacher 《Journal of Geodesy》2007,81(6-8):503-514

Troposphere parameters estimated from space-geodetic techniques, like the Global Positioning System (GPS) or Very Long Baseline Interferometry (VLBI), can be used to monitor the atmospheric water vapor content. Although the troposphere can only be monitored at discrete locations, the distribution of the instruments, at least the GPS antennas, can be assumed to be quasi-global. Critical in the data analysis are systematic effects within each single technique that significantly degrade the accuracy and especially the long-term stability of the zenith delay determination. In this paper, consistent time-series of troposphere zenith delays and gradients from homogeneously reprocessed GPS and VLBI solutions are compared for a time period of 11 years. The homogeneity of these completely reprocessed time-series is essential to avoid misinterpretations due to individual model changes. Co-located sites are used to investigate systematic effects and the long-term behavior of the two space-geodetic techniques. Both techniques show common signals in the troposphere parameters at a very high level of precision. The biases between the troposphere zenith delays are at the level of a few millimeters. On the other hand, long-term trends significantly differ for the two techniques, preventing climatological interpretations at present. Tests assume these differences to be due to mathematical artifacts such as different sampling rates and unmodeled semi-annual signals with varying amplitudes.  相似文献   

对地观测与地理信息系统   总被引：23，自引：2，他引：21  

李德仁 《地球科学进展》2001,16(5):689-693

20世纪地球科学进步的一个突出标志是人类开始脱离地球从太空观测地球（Earth Observation from Space）,并将得到的数据和信息在计算机网络以地理信息系统形式存储、管理、分发、流通和应用。比较全面地介绍了上述过程的若干关键技术：航空航天遥感技术、GPS技术和地理信息系统技术的最新发展及其未来计划。重点介绍了气象卫星、资源卫星、制图卫星、EOS计划以及我国航空航天遥感的主要成就;GPS全球定位系统及在我国的应用、卫星测高技术、我国的甚长基线干涉测量与卫星激光测距;GIS的发展历史及其特点、我国GIS的发展概况与现状等,最后提出“Geo-Information for all”的观点。  相似文献