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1.
N. Kameswara Rao V. R. Venugopal A. Patnaik 《Journal of Astrophysics and Astronomy》1985,6(3):153-157
VLA observations at 2 and 6 cm have been obtained for six hydrogen-deficient stars R CrB, HD 160641, BD — 9°4395, V348 Sgr,
MV Sgr and Sgrv Upper limits to the massloss rates have been estimated for some of these using the upper limits to the radio flux density.
National Radio Astronomy Observatory’s Very Large Array is operated by Associated Universities Inc. under contract with National
Science Foundation, USA 相似文献
2.
Observe是用于制订甚大阵 (theVeryLargeArray ,VLA)观测文件的软件。随着中国科学院创新工程的全面推进 ,利用VLA进行观测研究的中国天文学家逐渐增多 ,Observe软件的使用也日益广泛。简要介绍了Observe的主要功能和应用 ;并结合 2 0 0 0年 12月的观测文件 (AH72 1)的制订过程 ,给出了注意事项 ,供今后的VLA观测者参考 相似文献
3.
V. Migenes E. Lüdke R. J. Cohen M. Shepherd P. F. Bowers 《Astrophysics and Space Science》1995,224(1-2):515-516
We present recent radio interferometer measurements of the OH 1612 MHz maser emission from the OH/IR sources OH0.9+1.3 and OH357.31 obtained with the enhanced MERLIN. Some preliminary results are briefly discussed. These results are part of an on-going observational campaign to obtain the best radio maps of bright OH/IR stars with MERLIN, VLA and VLBA, in order to understand the nature and dynamics of their circumstellar matter and evolution. 相似文献
4.
Tao An Xiao-Yu Hong Wen-Xia Feng Jun-Hui Zhao Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai National Astronomical Observatories Chinese Academy of Sciences Beijing Harvard-Smithsonian Center for Astrophysics Garden Street MS Cambridge MA 《中国天文和天体物理学报》2004,4(6):527-532
We observed 1938-155, a broad line radio galaxy (BLRG), with the Very Large Array (VLA) at 90cm with an angular resolution of 6.8" × 4.0". The source consists of two components separated by 4 arcsec (- 20kpc, for H0 = 65km s-1 Mpc-1, q0 = 0.5) along the SE-NW direction. Both components show steep-spectra with a similar spectral index α - 0.83 ± 0.07 (Sv ∝ v-α). The bright double components are surrounded by a low-brightness cocoon. The radio properties of the two bright components are consistent with the hot spots produced by twin jets. An upper limit of - 0.0008 for the core dominance parameter (R) is inferred, suggesting there is no prominent radio core in the source. Assuming a modest viewing angle 30f77, a jet velocity is estimated - 0.07 c, based on the jet to counter-jet brightness ratio (J). The lower limit in jet speed inferred is consistent with no Doppler beaming effect on the jet. The radio galaxy 1938-155 could be an exceptional BLRG with no prominent radio core or jet. 相似文献
5.
Tao An Xiao-Yu Hong Wei-Hua WangShanghai Astronomical Observatory Chinese Academy of Sciences Shanghai National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2004,4(1):28-36
We present radio images of the compact steep spectrum (CSS) quasar 3C 286 acquired with the Very Large Array (VLA) at 8.4 and 22.5 GHz. The source exhibits a two-sided core-jet structure with a bright central component and two extended components one to the east (P.A. 100°) and another to the southwest (P.A. - 116°). From the compact core, an extension runs towards the southwest component up to - 0.7 arcsecond. The emission between the primary central component and the southwest component exhibits a knotty structure. A gradual change of the jet position angles from -135° to -120° in the inner southwest jet suggests a local bend. The position angle changes of the major eastern components E2 and El suggest that the eastern jet likely follows a curved trace. The bends in the jet trace may be associated with a relativistic precession or some interaction between the jet and the ambient matter. A mean spectral index of a22.58.4 - -0.76 (Sv ∝ va) is estimated for the core component. Steep spectra are also 相似文献
6.
文章简要介绍了浅海声传播损失的研究背景和基本理论方法。通过1/3倍频程滤波对浅海爆炸宽带信号的不同频段在浅海的传播损失情况进行了分析,描述了浅海环境对声传播损失的影响;同时在不知道先验信息的条件下,利用垂直阵声压数据成功地进行了简正波分离,并与理想条件下Kraken简正波模型计算出的结果进行了比较分析。 相似文献
7.
为确定浅埋软黏土中法向承力锚的位移破坏标准,利用实验室自行开发的电动伺服加载控制装置,对埋置在饱和软黏土中深度为3倍锚板宽度、系缆力角度为30°的法向承力锚模型进行了荷载和位移控制的静力加载试验。依据试验结果,以极限承载力与锚板宽度为参考,对锚板法向荷载与位移进行归一化处理,通过归一化曲线确定了法向承力锚的位移破坏标准,即破坏位移约为0.38倍锚板宽度。另外,依据锚板的尺寸、埋深及试验土体的强度条件,利用经验公式对锚的极限承载力进行了计算。结果表明,以该位移破坏标准确定的极限承载力与经验公式计算结果基本一致,两者相差均不超过10%,初步验证了该位移破坏标准的合理性。 相似文献
8.
Three supernova remnants (SNR) have been mapped in the galaxy M33 with the Very Large Array* (VLA) at 20 cm. The angular resolution
is ∼1.3 arcsec or ∼4 pc at a distance of 600 kpc and the rms noise is ∼0.04 mJy /beam. One of the radio sources shows evidence
for a shell structure with a size of ∼15 pc, confirming the SNR nature of this source. The second object is extended and may
well be a thick-shell SNR of size ∼12 pc. The third object is a small, presumably young SNR with a size of ∼4 pc. 相似文献
9.
Positions and proper motions obtained from observations by the very large array (VLA) and the multi-element radio-linked interferometer
network (MERLIN) are used to establish the link of the Hipparcos Celestial Reference Frame (HCRF) to the International Celestial
Reference Frame (ICRF). The VLA and MERLIN data are apparently the latest ones published in the literature. Their mean epoch
at around 2001 is about 10 years after the epoch of the Hipparcos catalogue and, therefore, the data are considered suitable
to check the Hipparcos link established at epoch 1991.25. The parameters of the link, i.e., the angles of frame orientation
and the angular rates of frame rotation, are estimated by fitting these parameters to the differences of the optical and radio
positions and proper motions of stars common to the Hipparcos catalogue and the VLA and MERLIN data. Both the estimates of
the angles of orientation and the angular rates of rotation show nearly consistent but insignificant results for all samples
of stars treated. We conclude that not only the size of the samples of 9–15 stars is too small, but also that the accuracy
of the radio positions and, above all, of the radio proper motions is insufficient, the latter being based on early-epoch
star positions of low accuracy. The present observational data at epoch 2001 suggest that maintenance of the Hipparcos frame
is not feasible at this stage. 相似文献
10.
Christopher J. Davis Michael D. Smith Jochen Eislöffel John K. Davies 《Monthly notices of the Royal Astronomical Society》1999,308(2):539-550
We present a comprehensive near-infrared study of two molecular bow shocks in two protostellar outflows, HH 99 in R Coronae Australis and VLA 1623A (HH 313) in Rho Ophiuchi. New, high-resolution, narrow-band images reveal the well-defined bow shock morphologies of both sources. These are compared with two-dimensional MHD modelling of molecular bows from which we infer flow inclination angles, shock speeds and the magnetic field in the pre-shock gas in each system. With combined echelle spectroscopy and low-resolution K -band spectra we further examine the kinematics and excitation of each source. Bow shock models are used to interpret excitation (CDR) diagrams and estimate the extinction and, in the case of VLA 1623, the ortho–para ratio associated with the observed H2 population. For the first time, morphology, excitation and kinematics are fitted with a single bow shock model.
Specifically, we find that HH 99 is best fitted by a C-type bow shock model (although a J-type cap is probably responsible for the [Fe ii ] emission). The bow is flowing away from the observer (at an angle to the line of sight of ∼45°) at a speed of roughly 100 km s−1 . VLA 1623A is interpreted in terms of a C-type bow moving towards the observer (at an angle to the line of sight of ∼75°) at a speed of ∼80 km s−1 . The magnetic field associated with HH 99 is thought to be orientated parallel to the flow axis; in VLA 1623A the field is probably oblique to the flow axis, since this source is clearly asymmetric in our H2 images. 相似文献
Specifically, we find that HH 99 is best fitted by a C-type bow shock model (although a J-type cap is probably responsible for the [Fe ii ] emission). The bow is flowing away from the observer (at an angle to the line of sight of ∼45°) at a speed of roughly 100 km s