Seeing Conditions at Sutherland. Results of the 1992/93 seeing campaign

In order to decide whether the seeing conditions at SAAO/Sutherland justify the erection of a 3.5 m telescope and also to compare Sutherland with the Gamsberg/Namibia site, a seeing campaign covering 15 months has been carried out. For direct comparison with the results of the seeing campaign at Gamsberg twenty years before the same QUESTAR telescope was employed. The seeing is determined by the scattering of the star-trail exposed on a film in the focal plane of the telescope. The campaign commenced in February 1992. Up to May 1993, data for 204 nights, that is 47.3% of the total number of nights, were collected. Due to wind speeds above 30 km h^-1, 25 out of the 204 nights were not considered in the final reduction. The useful 179 nights are evenly distributed over the campaign period. The median seeing value for the whole period is = 0.52. There are differences during the year: the best season gives = 0.42, the worst = 0.67. Each night was divided into three intervals, although data for each of the three intervals were not always available. Generally, there is an improvement in the seeing during the course of a night. The results are compared to the seeing values of Gamsberg/Namibia and ESO/La Silla.     

超新星遗迹X射线研究

在此介绍我们基于ＡＳＣＡ 和ＲＯＳＡＴ 等Ｘ 射线天文卫星,对３Ｃ３９７ 、Ｇ３２７ ．１１ ．１ 、Ｇ２１ ．５０ ．９ 和ＲＸＪ１７１３ ．７３９４６ 等超新星遗迹的物理特性进行的分析,简要地讨论了３Ｃ３９７ 的非平衡电离双热分量和双极泡结构以及Ｇ３２７ ．１１ ．１ 和Ｇ２１ ．５０ ．９ 中隐匿脉冲星的性质,并提出ＲＸＪ１７１３ ．７３９４６ 和ＡＤ３９３ 客星之间可能的关系。     

21世纪世界的资源和环境

20世纪世界人口从15亿增长到60亿.而经济成长更为快速,自1950年至今已增长4倍.目前世界人口每年增加8000余万人,至2050年将达到90亿,世界经济是否能持续发展以提升或维持现有的生活水准,值得研讨.资源的消长和环境的变迁是具有决定性的两大重要议题.     

耦合热传导的磁重联的数值模拟

磁重联被认为是太阳耀斑的产生机制,本文数值模拟在日冕中发生在磁重联过程,结果表明耀斑环的表观运动是磁重联的自洽结果;由重联点发出的慢激波对耀斑环的加热有贡献;耀斑环的上升并不意味着重联点的上升。     

V473 Lyrae: a Blazhko-effect Cepheid?

The amplitude spectra of the light curves of RR Lyrae Blazhko stars can often be typified by symmetrical triplets. It is shown that the same applies to V473 Lyr. Furthermore, the star is probably a radial pulsator – as is thought to be the case for the RR Lyrae stars – thus ruling out rotational splitting of a purely non-radial mode.     

BeppoSAX observations of the Seyfert 2 galaxies NGC 7172 and ESO 103-G35

We investigate the X-ray spectra of the type 2 Seyfert galaxies NGC 7172 and ESO 103-G35, using BeppoSAX observations, separated by approximately one year. We find that the X-ray spectra of both NGC 7172 and ESO 103-G35 can be well fitted using a power-law model with an Fe K α emission line at 6.4 keV. We did not find any statistically significant evidence for the existence of a reflection component in the X-ray spectra of these two galaxies. The continuum flux has decreased by a factor of approximately 2 during this period, in both objects. However, the spectral index as well as the absorption column have remained constant. We find weak evidence for the decrease of the normalization of the Fe K α emission line in a similar manner to the continuum in NGC 7172. We also report tentative evidence for a broad Fe K α line in agreement with previous ASCA observations. In contrast, in the case of ESO 103-G35 the line flux does not change while its width remains unresolved.     

The fraction of galaxies that contain active nuclei and their accretion rates

We investigate the relationship between the present-day optical luminosity function of galaxies and the X-ray luminosity function of Seyfert 1s to determine the fraction of galaxies that host Seyfert 1 nuclei and their Eddington ratios. The local type 1 active galactic nuclei (AGN) X-ray luminosity function is well reproduced if ∼1 per cent of all galaxies are type 1 Seyferts which have Eddington ratios of ∼10⁻³. However, in such a model the X-ray luminosity function is completely dominated by AGN in E and S0 galaxies, contrary to the observed mix of Seyfert host galaxies. To obtain a plausible mix of AGN host galaxy morphologies requires that the most massive black holes in E and S0 galaxies accrete with lower Eddington ratios, or have a lower incidence of Seyfert activity, than the central black holes of later-type galaxies.     

Spectral index determination between 408 MHz and 5 GHz in the northern sky

We present the joint analysis of two 5-GHz interferometric surveys of the northern sky, taken with different baselines. The two surveys were carried out on the Jodrell Bank 5-GHz interferometer based at Manchester. The Maximum Entropy Method is used to check the consistency of the two surveys and the final two-dimensional maps are used, together with low-frequency full sky surveys, to put constraints on the Galactic spectral index. It is found that synchrotron emission is the dominant process at high Galactic latitudes below 5 GHz.