Praesepe – two merging clusters?

A membership catalogue for Praesepe was compiled and split into four mass bins. A contour plot indicates the presence of a subcluster some 3 pc from the centre of the cluster, of approximately 30 M_⊙. A tidally truncated King profile was fitted to the remainder of the cluster and the tidal radius is found to be 12.1 pc; the mass of the cluster (excluding the subcluster) is 630 M_⊙. From the calculated velocity dispersions we find that the cluster appears to have too much kinetic energy and should be rapidly disintegrating. X-ray data suggest that there may be an age spread between the main core stars and the subcluster stars. This leads us to the conclusion that Praesepe is two merging clusters.     

X-ray spectral evolution of low-mass X-ray binary GX 349+2

We present the results of a systematic investigation of spectral evolution in the Z source GX 349+2, using data obtained during 1998 with the Proportional Counter Array (PCA) on-board the RXTE satellite. The source traced a extended normal branch (NB) and flaring branch (FB) in the colour–colour diagram (CD) and the hardness-intensity diagram (HID) during these observations. The spectra at different positions of the Z-track were best fitted by a model consisting of a disc blackbody and a Comptonized spectrum. A broad (Gaussian) iron line at ∼6.7 keV is also required to improve the fit. The spectral parameters showed a systematic and significant variation with the position along the Z-track. The evolution in spectral parameters is discussed in view of the increasing mass accretion rate scenario, proposed to explain the motion of Z sources in the CD and the HID.     

Aegir脊及邻区重磁异常及构造特征

为研究北极地区挪威海内Aegir脊及邻区断裂构造特征,为北极地区油气勘探提供方向,在斯克里普斯海洋研究所发布的研究区重力数据（网格数据）基础上填充最新船测数据,对已有重磁资料进行异常分离、滑动平均和重磁场边界识别。目前,研究区的特征断裂和构造单元划分尚不清楚。根据异常极值带、异常带走向、异常梯度带变化程度等,对研究区进行了断裂识别和构造单元划分。研究表明：重磁异常特征呈NNE—NW—NE向展布,重力异常呈现高低分带,反映出该区基底隆坳相间的格架。根据重磁异常与断裂对应关系,识别出4个构造走向和7条主要断裂,划分出Mohns脊、扬马延微陆块、东扬马延断裂带、西扬马延断裂带、Aegir脊、东扬马延深海盆地和挪威深海盆地等7个构造单元。     

基于地磁参数和子午线收敛角计算的井斜方位角校正方法

井斜方位角的校正对于定向井轨迹控制、中靶分析有非常重要的意义。通过分析大地坐标与高斯克吕格投影坐标之间的关系,根据地磁场球谐函数模型,地磁参数和子午线收敛角的计算模型,提出了实现方式和求解步骤,并编制了相应的计算软件。通过实例计算与分析,表明地磁参数和子午线收敛角的准确计算对于定向井轨迹控制的重要性。     

Wavelength Dependence of the Orbital Variability of the Eclipsing Nova-Like Object Dw Uma

Results of three-colour VRI CCD photometry are presented obtained during 11 nights in 2001. Twelve new minima timings are derived. The eclipse depth decreases with wavelength, being equal to 1.28, 1.13 and 1.02 for V, R and I, respectively. The instrumental magnitudes and colours are tabulated for the mid-eclipse, out-of-eclipse part and the eclipsed component. The V−R colour of the eclipsed component of emission is by 0.22 mag bluer than that for mid-eclipse, indicating a much higher temperature of the eclipsed region.