共查询到20条相似文献，搜索用时 93 毫秒
1.
１９９３年１１月４日－１２月１５日，上海天文台氢脉泽安装在澳大利亚帕凯期天文台，本文给出在此期间这台氢脉泽的试验结果，这次试验的主要目的是测定这台氢脉泽作为ＶＬＢＩ频率标准的性能。 相似文献
2.
俞志尧 《中国天文和天体物理学报》1997,(2)
用多重分离的旋转膨胀环模型，分析了旋涡星系Ｍ３３的ＨＩＩ区复合体ＩＣ１３３中的１４个脉泽源斑的ＶＬＢＩ相对位置图，发现这１４个Ｈ２Ｏ脉泽源斑在ＨＩ区复合体盘上成环状，分布在二个不同的旋转膨胀盘环上．同时，也得到这１４个Ｈ２Ｏ脉泽源斑的运动学特性． 相似文献
3.
用多重分离的旋转膨胀环模型，分析了旋涡星系Ｍ３３的ＨＩＩ区复合体ＩＣ１３３中的１４个Ｈ２Ｏ脉泽源斑的ＶＬＢ相对位置图，发现这１４个Ｈ２Ｏ脉泽源斑在ＨＩＩ区复合体盘上成形状，分布在二个不同的旋转膨胀盘环上，同时，也得到这１４个Ｈ２Ｏ脉泽源 运动学特性。 相似文献
4.
利用甚长基线干涉仪，在１６６５ＭＨｚ频率上，观测超致密氢ＩＩ区Ｇ４５．０７＋０．１３的左右圆偏振羟基（ＯＨ）分子脉泽辐射．利用多条纹率成图方法，获得了这个区域２０ｍａｓ相对位置精度的脉泽结构图．除两个弱子源以外，所有脉泽子源都位于彗状结构氢ＩＩ区“彗头”的前沿．脉泽团离致密氢ＩＩ区中心投影距离为０＂．４．在完全饱和辐射的假设下，估计脉泽活动区具有氢分子数密度约为４．５×１０８（Ｈ２）ｃｍ－３．在脉泽源中，发现一对Ｚｅｅｍａｎ对，从它们的ＬＳＲ速度差，导出脉泽区的磁场约为３ｍＧ，方向为远离地球方向．在致密氢ＩＩ区Ｇ４５．０７＋０．１３彗头附近的脉泽团的直径为６×１０１６ｃｍ．这与Ｇ３４．０３＋０．２的观测结果很类似．这给解释彗状结构的氢ＩＩ区的各种模型提供了一个可靠的观测约束条件． 相似文献
5.
本文作者用美国ＮＲＡＯ，ＧｒｅｅｎＢａｎｋ４３ｍ和中国科学院紫金山天文台德令哈１３．７ｍ射电望远镜，对新近发现的水６１６—５２３脉泽相隔约１年的三次观测结果作了本地静止标准速度时变的研究，在分析实测结果时采用了参量ＬＳＲ速度延展（Ｖｓｐｄ），相继两历元观测的谱征峰值速度极差（ＤＶ）和速度位移（ＤＶ）．结果表明可将分析样本归纳为两类：Ａ类，微弱多数样本的速度时变给出的谱征位移显示脉泽结的替代效应．这种情况是在观测波束内存在若干未分解的脉泽斑引起的，主要受制于共同激发源的简单运动；Ｂ类，余下的样本给出较大的速度极差，呈现脉泽结整体的运动，涉及激发源的加速和减速以及抽运机制． 相似文献
6.
我们从对Ｏｒｉｏｎ－ＫＬ星云中ＯＨ１６６５ＭＨｚ脉泽的单基线干涉观测的分析中，提出一种新的外流模型，即多重分离的旋转膨胀环。这种模型与观测结果是一致的。通过对２４ｋｍ单基线观测得到的１９个ＯＨ１６６５ＭＨｚ脉泽斑点的相对位置图进行分析、统计、拟合和计算，得到这１９个ＯＨ１６６５ＭＨｚ脉泽斑点分析分布在三个旋转膨胀环上。这个旋转膨胀环的视距分别为３＂．８５，５＂．８７，６＂．０；对应的环半径分别为１ 相似文献
7.
南天区耀变体的VLBI研究 总被引：2，自引：2，他引：0
本报道南天区５ＧＨｚＶＬＢＩ的第二轮观测，第二轮观测是在１９９３年５月期间进行的，共观测２５个射电源，检测到２４个源，获得了２３个南天区耀变体的ＶＬＢＩ高分辨率的图象，其中１５个是第一次ＶＬＢＩ成图，７个高能γ射电源，１２个泊呈现核－喷流结构，其余１１个源是单一的致密核，未发现致密双源。有两个源可能有视超光速现象。 相似文献
8.
本文报道南天区５ＧＨｚＶＬＢＩ的第二轮观测．第二轮观测是在１９９３年５月期间进行的，共观测了２５个射电源，检测到２４个源，获得了２３个南天区耀变体（Ｂｌａｚａｒ）的ＶＬＢＩ高分辨率的图象，其中１５个是第一次ＶＬＢＩ成图，７个是高能（＞１００ＭｅＶ）γ射电源，１２个源呈现核－喷流结构，其余１１个源是单一的致密核，未发现致密双源．有两个源可能有视超光速现象． 相似文献
9.
本文给出利用中国、意大利、南非射电望远镜对一个近赤道源样本在５ＧＨｚ频率上进行ＭＫ２ＶＬＢＩ普测中１０颗弱源的相关流量和其中部分源用ＨａｒｔＲＡＯ望远镜观测的总流量值，作为进一步的ＭＫ３或ＶＬＢＡ记录系统的ＶＬＢＩ观测依据． 相似文献
10.
ＶＬＢＩ──全人类分一块蛋糕的艺术南仁东甚长基线干涉测量，简称ＶＬＢＩ。是６０年代发展起来的新技术，使用这种方法可以提高射电望远镜的分辨率。随着ＶＬＢＩ技术的发展，它不但应用于天体物理观测，而且对天体测量、天文地球动力学和大地测量等学科也有广泛的应用... 相似文献
11.
J. N. McCallum S. P. Ellingsen J. E. J. Lovell C. J. Phillips J. E. Reynolds 《Monthly notices of the Royal Astronomical Society》2009,392(4):1339-1362
We have used the Long Baseline Array to observe the Circinus Galaxy H2 O megamasers on two epochs separated by 49 d. The masers were observed to be highly variable, consistent with previous studies. We observe rapid variations in the linewidth and central velocity of the maser's spectral profile. The characteristics of these spectral variations suggest that the masers have an anisotropic structure, with axial ratios ≲5, and display velocity gradients in their microarcsecond structure. We also find a strong anticorrelation between the linewidth and the modulation index of the maser features and a relationship between the modulation index and characteristic time-scale of the variations. These various phenomena can all be simply explained through a model where the rapid variations in the masers are produced by quenched diffractive scintillation in the presence of modest velocity gradients in the maser emission.
The very long baseline interferometry (VLBI) images are consistent with previous high-resolution observations and show maser emission arising both in a circumnuclear accretion disc, and in a low-velocity outflow. We find no systematic differences in the variability properties of the disc and outflow masers. The VLBI images reveal that there is considerable spectral blending in single-dish spectra of the Circinus megamasers.
In addition to the VLBI imaging we also used these observations to look for a time delay in the intensity variations observed at the different telescopes in the array, as expected for scintillation-induced variability. No time delay was detected, which allows us to place a lower limit on the velocity of the interstellar medium during these observations 22 km s−1 for the second epoch. We conclude that any future attempts to measure a time delay in this source should utilize intercontinental baselines to increase the chances of success. 相似文献
The very long baseline interferometry (VLBI) images are consistent with previous high-resolution observations and show maser emission arising both in a circumnuclear accretion disc, and in a low-velocity outflow. We find no systematic differences in the variability properties of the disc and outflow masers. The VLBI images reveal that there is considerable spectral blending in single-dish spectra of the Circinus megamasers.
In addition to the VLBI imaging we also used these observations to look for a time delay in the intensity variations observed at the different telescopes in the array, as expected for scintillation-induced variability. No time delay was detected, which allows us to place a lower limit on the velocity of the interstellar medium during these observations 22 km s
12.
中国计划于2025年左右建立月球轨道VLBI (Very Long Baseline Interferometer)测站,将会搭载被动型星载氢钟作为时间频率标准.由于是首次在VLBI观测中使用星载氢钟,需要研究和验证其可行性.因此,利用星载氢钟作为频率基准开展了VLBI观测.实验时,分别使用主动型地面氢钟和被动型星载氢钟作为频率基准,利用上海天文台佘山25 m射电望远镜和其他测站对我国火星探测器天问一号进行了交替VLBI观测.数据处理分析结果表明,基于地面氢钟与星载氢钟的VLBI残余群时延标准差均在0.5 ns以内,表明星载氢钟可满足深空探测VLBI测定轨的精度要求,验证了其作为月球VLBI测站频率基准的可行性. 相似文献
13.
《Chinese Astronomy and Astrophysics》2022,46(3):297-308
China plans to establish a lunar orbital VLBI (Very Long Baseline Interferometer) station around 2025, which will carry a space passive hydrogen maser as the time and frequency reference. Since it is the first time to use a space passive hydrogen maser for VLBI observation, its feasibility needs to be studied and verified. Therefore, we carried out VLBI observations using the space passive hydrogen maser as the frequency reference. In the experiment, the active hydrogen atomic clock and space passive hydrogen maser were used as the frequency standard, and the alternate VLBI observations of China’s Mars probe TW1 (Tianwen 1) were carried out using the 25 m radio telescope at Sheshan, Shanghai, and other VLBI stations. The results of data processing and analysis show that the standard deviation of VLBI residual group delay based on both active hydrogen atomic clock and space passive hydrogen maser are within 0.5 ns, which indicates that the space passive hydrogen maser can meet the accuracy requirements of VLBI measurement for deep space exploration, and verify its feasibility as the frequency standard of lunar orbital VLBI stations. 相似文献
14.
We present VLBI observations of 6.7 and 12.2 GHz methanol masers in three star-forming regions, NGC7538, W75N and S252. Our results reveal linear structures in the VLBI maps and monotonic velocity gradients in the three sources. All these results are consistent with Keplerian disks of diameter of 1000–2000 AU around young stars of mass (10–30) M. 相似文献
15.
V. V. Andreyanov 《Experimental Astronomy》1999,9(3):103-117
Space VLBI's highly dynamic geometry, ability to access the space radio telescope (SRT) only via distant communication links, very expensive mission cost, and scientific goals define the basic strategy and scenario for mission control and radio source observations. These are very different from those for ground-based VLBI. Space VLBI strategy must be based on the limitation of SRT repointings, periodic orbit determination before astronomical observations, preliminary preparation and checking of space and ground facilities, and recommended observing sequences and modes. A control and observation scenario is considered for an in-orbit-checkout period, and also for short (1-orbit – 1 week) and long (1 week and more) observation sessions. Examples and illustrations are given for the Radioastron space VLBI Project. 相似文献
16.
Yu Zhiyao 《Astrophysics and Space Science》1992,192(1):53-62
By use of the data for VLBI observation of SiO masrs, and MERLIN observation of H2O and OH masers of VX Sgr, we found that the SiO, H2O, OH 1665/7, OH 1612 masers occur on a few separated shells, and the order of magnitude of the radii of their corresponding shells is 1014, 1015, 1016 cm, respectively. The field of the expanding velocity of the shells is obtained. It is important to note ice-layer covers on the surface of dust and grain for outlayer envelopes. 相似文献
17.
The European VLBI Network (EVN) has been used to make phase referenced, wide-field (several arcminute) spectral line observations of the 6.7-GHz methanol maser emission towards W51. In the W51 Main region, the bulk of the methanol is offset from an UCHii region. This probably indicates the methanol emission arises at the interface of the expanding UCHii region and not from an edge-on circumstellar disc, as previously suggested. Near the W51 IRS2 region, the methanol emission is associated with a very compact, extremely embedded source supporting the hypothesis that methanol masers trace the earliest stages of massive star formation. As well as these two well-studied sites of star formation, many previously unknown regions star formation are detected, demonstrating that methanol masers are powerful means of detecting young massive stars. 相似文献
18.
M. D. Gray M. Wittkowski M. Scholz E. M. L. Humphreys K. Ohnaka D. Boboltz 《Monthly notices of the Royal Astronomical Society》2009,394(1):51-66
We describe a combined dynamic atmosphere and maser propagation model of SiO maser emission in Mira variables. This model rectifies many of the defects of an earlier model of this type, particularly in relation to the infrared (IR) radiation field generated by dust and various wavelength-dependent, optically thick layers. Modelled masers form in rings with radii consistent with those found in very long baseline interferometry (VLBI) observations and with earlier models. This agreement requires the adoption of a radio photosphere of radius approximately twice that of the stellar photosphere, in agreement with observations. A radio photosphere of this size renders invisible certain maser sites with high amplification at low radii, and conceals high-velocity shocks, which are absent in radio continuum observations. The SiO masers are brightest at an optical phase of 0.1–0.25, which is consistent with observed phase lags. Dust can have both mild and profound effects on the maser emission. Maser rings, a shock and the optically thick layer in the SiO pumping band at 8.13 μm appear to be closely associated in three out of four phase samples. 相似文献
19.
J. Nakajima Y. Koyama M. Sekido N. Kurihara T. Kondo M. Kimura N. Kawaguchi 《Experimental Astronomy》2001,11(1):57-69
We report on the detection of VLBI fringes from quasars by a new VLBI system operating at 1 Gbps (1024 Mbits-per-second). Newly developed 1024 Msps (mega sample-per-second) AD samplers and 1024 Mbps recorders were used for the observations. A correlator with external buffers was used for the 1024 Mbps correlation processing of the tapes data.Our new VLBI system enabled 1024 Mbps VLBI, and this allowed the sampling of a 512 MHz bandwidth from a radio telescope receiver. This is the highest sampling speed ever used for VLBI, and the widest bandwidth used for VLBI observation. Initial sensitivity as evaluated by SNR comparison with earlier VLBI systems produced results to matched the expanded bandwidth. In our first observations, simultaneous optical fibre linked real-time VLBI observations were made to check the validity of data and precisely detemine the clock offsets among the radio telescopes. 相似文献
20.
VLBI是进行高分辨率脉冲星观测研究的重要手段.脉冲星信号是非常微弱的脉冲序列,其VLBI观测面临多种挑战.在数据相关过程中采用有效技术提取脉冲星信号可提高观测成功率和精度.DiFX(Distributed FX-style Software Correlator)是目前国际上流行的开源软件相关处理机,它采用非相干消色散技术和“脉冲星数据分箱技术”(Pulsar Binning),在脉冲星VLBI观测数据的相关处理方面具有优异的性能.介绍了DiFX的构架,安装、调试方法,并对利用DiFX处理脉冲星VLBI观测数据的进展情况进行论述.利用单机环境下的DiFX,在普通模式和Pulsar Binning模式下对中国VLBI网(CVN)第一次脉冲星观测数据进行相关处理;利用德国马普射电天文研究所集群计算环境下的Bonn-DiFX,在Pulsar Binning模式下对流量仅有2.6 mJy的毫秒脉冲星PSRJ1022+1001的欧洲VLBI网(EVN)观测数据成功进行相关处理.最后,对使用DiFX处理脉冲星观测数据情况进行总结,并展望了今后CVN开展脉冲星观测研究的前景. 相似文献