利用反射率因子垂直廓线填补雷达波束遮挡区的方法研究

新一代天气雷达很多位于地形复杂的山区,地形遮挡形成观测盲区,严重影响了新一代天气雷达数据的应用效果。利用基于高分辨率地形数据计算的波束遮挡信息,依据反射率因子垂直廓线,由高仰角无遮挡的反射率因子观测数据得到低仰角完全遮挡区的数据。以杭州雷达为例,通过直接对比反射率因子值和对比填补前后雷达估算降水效果两种途径检验了填补效果,结果表明：填补与观测“真值”有很好的一致性,填补后降水估算效果优于填补前。本文提出一种填补低仰角完全遮挡区的方法,适用于均匀性降水系统。     

大质量恒星形成区样本外向流的高灵敏度搜寻

对13个大质量恒星形成区样本进行了SiO(2-1)、CH_3OH(2-1)和C~(34)S(2-1)热线的观测.在9个分子云核中,3条热线同时被探测到.这9个SiO探测中,有3个是新探测到的且它们强度都相对较弱.所有探测到的谱线都有较明显的线翼,这可能是外向流出现的证据.SiO谱线的线宽最宽,这也更进一步表明SiO辐射可能是来自高速的外向流,即更靠近外向流的激发源.估算了各分子谱线的旋转温度,柱密度和相对元素丰度.结果表明SiO和CH_3OH元素丰度之间有较好的相关性,相关系数R=0.77,但是SiO和C~(34)S元素丰度之间却没有任何相关性.     

The Tully-Fisher relations of the Eridanus group of galaxies

The Tully-Fisher (TF) or the luminosity-linewidth relations of the galaxies in the Eridanus group are constructed using the HI rotation curves and the luminosities in the optical and in the near-infrared bands. The slopes of the TF relations (absolute magnitudevs log2V _flat) are −8.6 ± 1.1, −10.0 ±1.5, −10.7 ±2.1, and −9.7 ±1.3 in the R, J, H, and K bands respectively for galaxies having flat HI rotation curves. These values of the slopes are consistent with those obtained from studies of other groups and clusters. The scatter in the TF relations is in the range 0.5-1.1 mag in different bands. This scatter is considerably larger compared to those observed in other groups and clusters. It is suggested that the larger scatter in the TF relations for the Eridanus group is related to the loose structure of the group. If the TF relations are constructed using the baryonic mass (stellar +HI + Helium mass) instead of the stellar luminosity, nearly identical slopes are obtained in the R and in the near-infrared bands. The baryonic TF (baryonic massvs log2V _flat) slope is in the range 3.5–4.1.     

全球定位系统的新进展(讲座三)——GPS中的民用测距码

介绍了C/A码、L2C码以及L5码的生成方式、测距精度及特性,并对GPS系统中测距码的扩充作了简要介绍。     

Deep low-frequency observations with the Giant Metrewave Radio Telescope: a search for relic radio emission

We present deep multifrequency observations using the Giant Metrewave Radio Telescope (GMRT) at 153, 244, 610 and 1260 MHz of a field centred on J0916+6348, to search for evidence of fossil radio lobes which could be due to an earlier cycle of episodic activity of the parent galaxy, as well as haloes and relics in clusters of galaxies. We do not find any unambiguous evidence of episodic activity in a list of 374 sources, suggesting that such activity is rare even in relatively deep low-frequency observations. We examine the spectra of all the sources by combining our observations with those from the Westerbork Northern Sky Survey (WENSS), NRAO (National Radio Astronomy Observatories) VLA (Very Large Array) Sky Survey (NVSS) and the Faint Images of the Radio Sky at Twenty-Centimeters Survey (FIRST). Considering only those which have measurements at a minimum of three different frequencies, we find that almost all sources are consistent with a straight spectrum with a median spectral index,  α∼ 0.8 [S(ν) ∝ν^−α  ], which appears steeper than theoretical expectations of the injection spectral index. We identify 14 very steep-spectrum sources with  α≥ 1.3  . We examine their optical fields and discuss the nature of some of these sources.     

The IPHAS-POSS-I proper motion survey of the Galactic plane

We present millimetre observations of a sample of 12 high-redshift ultraluminous infrared galaxies (ULIRGs) in the extended growth strip (EGS). These objects were initially selected on the basis of their observed mid-IR colours (  0.0 < [3.6]−[4.5] < 0.4  and  −0.7 < [3.6]−[8.0] < 0.5  ) to lie at high redshift  1.5 ≲ z ≲ 3  , and subsequent 20–38 μm mid-IR spectroscopy confirms that they lie in a narrow redshift window centred on   z ≈ 2  . We detect 9/12 of the objects in our sample at high significance  (>3σ)  with a mean 1200 μm flux of  〈 F _1200 μm〉= 1.6 ± 0.1  mJy. Our millimetre photometry, combined with existing far-IR photometry from the Far-IR Deep Extragalactic Legacy Survey (FIDELS) and accurate spectroscopic redshifts, places constraints both sides of the thermal dust peak. This allows us to estimate the dust properties, including the far-IR luminosity, dust temperature and dust mass. We find that our sample is similar to other high- z and intermediate- z ULIRGs, and local systems, but has a different dust selection function than submillimeter-selected galaxies. Finally, we use existing 20-cm radio continuum imaging to test the far-IR/radio correlation at high redshift. We find that our sample is consistent with the local relation, implying little evolution. Furthermore, this suggests that our sample selection method is efficient at identifying ultraluminous, starburst-dominated systems within a very narrow redshift range centred at   z ∼ 2  .