Interstellar Extinction and the Intrinsic Colors of Classical Cepheids in the Galaxy, the LMC, and the SMC

New methods are applied to samples of classical cepheids in the galaxy, the Large Magellanic Cloud, and the Small Magellanic Cloud to determine the interstellar extinction law for the classical cepheids, R _B:R _V:R _I:R _J:R _H:R _K= 4.190:3.190:1.884:0.851:0.501:0.303, the color excesses for classical cepheids in the galaxy, E(B-V)=-0.382-0.168logP+0.766(V-I), and the color excesses for classical cepheids in the LMC and SMC, E(B-V)=-0.374-0.166logP+0.766(V-I). The dependence of the intrinsic color (B-V)₀ on the metallicity of classical cepheids is discussed. The intrinsic color (V-I)₀ is found to be absolutely independent of the metallicity of classical cepheids. A high precision formula is obtained for calculating the intrinsic colors of classical cepheids in the galaxy: (<B>-<V>)₀=0.365(±0.011)+0.328(±0.012)logP.     

VLA and MERLIN observations of RZ Cassiopeiae

We present radio interferometric observations of the Algol-type binary system RZ Cassiopeiae made with the VLA and MERLIN arrays at 6 cm over an incomplete orbital cycle of the system (1.195 d). We detected RZ Cas with both instruments. The images were unresolved in both cases, with angular extents comparable to the synthesized beams. The peak flux density in the VLA image was 1.14 mJy beam⁻¹ and in the MERLIN image it was 0.93 mJy beam⁻¹. The derived brightness temperatures are  4.02 × 10⁸  and  4.35 × 10⁸ K  and the effective electron energies are 0.347 and 0.346 MeV for the MERLIN and VLA data respectively. The radio light curve shows an interesting modulation centred close to the primary eclipse which seems to correlate with ASCA SIS observations of the system. The results can be interpreted as an emitting region on the outer hemisphere of the cool component aligned along the centroid axis of the binary system.     

TheROSAT survey of extreme UV sources: a new window on the universe

This paper discusses the first all-sky suvey of cosmic extreme ultra-violet sources, discovered by theROSAT Wide Field Camera. Details of the instrument and the survey are presented, with comparisons made to previous selected surveys in the X-ray regime. The subsequent optical identification program is described, and the major results summarized. I then discuss the main classes of EUV emitters: active chromosphere stars and hot white dwarfs, and describe the importance of EUV obserevations in understanding the astrophysics of these objects. Many bright, and relatively nearby, sources have been identified with hitherto unrecognized active stars, representing the extremes in chromospheric and coronal activity, be it binary or age related. Many new hot DA white dwarfs have also been indentified, and the most exciting result in this area is the discovery that significant traces of heavier elements (e.g. C, N, O, Si, Fe & Al) exist in their atmospheres, substantially increasing their EUV opacities. The importance of hot white dwarfs as standard candles in probing the local interstellar medium is also discussed. Miscellaneous counterparts (AGN, PNN, O-B stars and CVs) that make up the rest of the sample of EUV sources are also briefly mentioned. I conclude the paper with a discussion of the new magnetic cataclysmic variables discovered at SAAO, which have been the subject of intensive follow-up observations.     

The circumstellar shells of carbon miras

The relation between mass loss rate and pulsation period in carbon Miras is discussed. The dust mass loss rate is very low (about 2 × 10^–10 M/yr) up to aboutP = 380 days, where there is a sudden increase. ForP > 400 days there is a linear relation between logM andP. The change in the mass loss rate near 380 days may be related to radiation pressure on dust becoming effective in driving the outflow.     

Environmental variables related to wheat yields in the semiarid pampa region of Argentina

The current paper analyses various environmental parameters in relation to wheat yields in Bordenave, Province of Buenos Aires, Argentina. The variables used are: precipitation (ppt), maximum (Tx) and minimum temperature (Tmi) as well as those obtained by applying the Palmer model. Decadic and phenological scales are used for data corresponding to the period 1977–2000. The stepwise method is used to obtain a multi-variate equation to calculate yield taking into account environmental variables only. For a five variates model the coefficient of determination, R² equals 95.79% and the standard error of estimation is 129.0 kg ha⁻¹. In the sample yields, the incidence of total variability for thermal variables is 42.7% and for hydrological variables, 53%. The value and sign of the correlation coefficients were analysed throughout the cultivation cycle. The α coefficient is mainly responsible for yield variance during tillering and stem elongation. There is good correlation with the values of Palmer's Drought Severity Index (PDSI) for the flowering and grain filling stages.     

夏季东太湖光合有效辐射衰减特征及其对沉水植物恢复的指示

水下光照分布是影响水生态系统的重要因素,研究光合有效辐射衰减特征对于沉水植物恢复具有一定的指导意义.根据沉水植物生物量资料,将东太湖划分为沉水植物茂盛区、沉水植物稀疏区和无植物区3种区域.基于2019年夏季原位水下光场资料,探讨了东太湖光衰减特性和光照衰减因子的空间差异以及不同区域内的主导衰减因子,分析了东太湖的稳态阶段和富营养化水平,并阐述了真光层深度与透明度的关系,以期为东太湖沉水植物恢复和保护提供相关资料.结果表明:东太湖不同区域光衰减特性差异显著,光合有效辐射衰减系数(k d(PAR))在0.73~11.80 m^-1之间变化,真光层深度范围为0.39~6.31 m.不同区域的无机悬浮物和有机悬浮物浓度存在显著性差异,稀疏区叶绿素a浓度显著高于茂盛区,而与无植物区没有显著差异,有色可溶性有机物(CDOM)吸收系数在3种区域无显著性差异.k d(PAR)与无机、有机悬浮物的线性拟合效果较好,而与叶绿素a、CDOM拟合较差.水体吸收和散射作用是茂盛区光衰减的主要原因,无植物区域主导衰减因子仅有无机悬浮物,稀疏区由叶绿素a和无机悬浮物共同主导,是生态修复需要重点关注的区域,有机悬浮物和CDOM对东太湖光照衰减没有太大影响.东太湖目前正处于从草型稳态向藻型稳态过渡的阶段,整个湖泊属于富营养水平,真光层深度大约为透明度的2.7倍.     

PLS法与隧道围岩稳定性分类

围岩稳定性是隧道工程支护设计的基本参数,采用偏最小二乘回归法,综合考虑多因变量影响因素,对隧道围岩稳定性分类进行回归建模,并取得较好效果.