Reflection effect in close binaries. II. Distribution of emergent radiation from the irradiated component along the line of sight

We have calculated the effects of irradiation from a point source observed at infinity. Plane-parallel approximation and spherically-symmetric approximations are employed in calculating the self-radiation field for the sake of comparison. It is found that there are considerable changes in the radiation received at infinity between the approximation of plane-parallel stratification and spherical symmetry.     

拉萨紫外辐射特征分析及估算公式的建立

本文利用2005~2010年的辐射观测资料对拉萨地区紫外辐射的时间变化特征及紫外辐射与总辐射比值的变化特征进行了分析,结果表明,紫外辐射与太阳总辐射的变化规律基本一致,日变化表现为正午大、早晚小;季变化特征是夏季6月最大,冬季1月最小.紫外辐射日累积值6年平均为0.87 MJ·m-2·d-1;紫外辐射有逐年递减的趋势.紫外辐射与总辐射比值也存在着明显日变化,表现为正午大、早晚小的规律;其季节变化也是夏季最大,冬季最小.紫外辐射与总辐射比值6年平均为0.0418;紫外辐射与总辐射比值也呈现逐年递减的趋势.利用2010年大气质量数和晴空指数,建立了适合于拉萨紫外辐射估量的公式,估算值的瞬时值与观测值的平均相对误差最大为8.66%,紫外辐射日累积重构值与观测值平均相对误差仅为5.5%.     

光合有效辐射和紫外辐射测量标准的性能验证

2010年中国气象局建立了气象行业光合有效辐射和紫外辐射测量标准.标准建成后,标准器的各项技术性能指标必须经过实际测试来验证.通过对光谱辐射计的波长精密度、准确度、杂散光、重复性、稳定性、探头余弦响应等参数的测试验证,以及对整个标准的测量误差来源及不确定度的分析和评定,得以验证紫外辐射测量标准DTMc300双单色仪光谱辐射计满足世界气象组织(WMO)相关规定的技术指标要求.     

河南省紫外线辐射分布规律及影响因素研究

利用2005年以来的河南省18个地市级气象台站的紫外线辐射监测数据,分析了河南省紫外线辐射的时空分布特征,并定量分析了云量、能见度及相对湿度等因素对紫外线辐射的影响.结果表明:河南省紫外线辐射年平均值总体表现为中部和南部较高;冬季西北地区紫外线辐射较高,夏季在西部、豫东南到豫北西部有两个高值带;季紫外线辐射均值表现为春夏季高、秋冬季低的特点.紫外线辐射强度与总云量、低云量及相对湿度呈显著负相关,而与能见度呈显著正相关.     

Temperature-dependent photoabsorption cross-sections of cyanoacetylene and diacetylene in the mid- and vacuum-UV: Application to Titan's atmosphere

Cyanoacetylene (HC₃N) and diacetylene (C₄H₂) play an important role in the photochemistry of Titan's atmosphere, in part because of their strong absorption between 110 and 180 nm. Accurate photoabsorption cross-sections at temperatures representative of Titan's atmosphere are required to interprete Cassini observations and to calculate photolysis rates used in photochemical models. Using synchrotron radiation as a tunable vacuum ultraviolet (VUV) light source, we have measured absolute photoabsorption cross-sections of C₄H₂ and HC₃N with a spectral resolution of 0.05 nm in the region between 80 and 225 nm and at different temperatures between 173 and 295 K. The measured cross-sections are used to model transmission spectra of Titan atmosphere in the VUV.     

iVINE – Ionization in the parallel tree/sph code VINE: first results on the observed age-spread around O-stars

We present a three-dimensional, fully parallelized, efficient implementation of ionizing ultraviolet (UV) radiation for smoothed particle hydrodynamics ( sph ) including self-gravity. Our method is based on the sph / tree code vine . We therefore call it iVINE (for Ionization + VINE). This approach allows detailed high-resolution studies of the effects of ionizing radiation from, for example, young massive stars on their turbulent parental molecular clouds. In this paper, we describe the concept and the numerical implementation of the radiative transfer for a plane-parallel geometry and we discuss several test cases demonstrating the efficiency and accuracy of the new method. As a first application, we study the radiatively driven implosion of marginally stable molecular clouds at various distances of a strong UV source and show that they are driven into gravitational collapse. The resulting cores are very compact and dense exactly as it is observed in clustered environments. Our simulations indicate that the time of triggered collapse depends on the distance of the core from the UV source. Clouds closer to the source collapse several 10⁵ yr earlier than more distant clouds. This effect can explain the observed age spread in OB associations where stars closer to the source are found to be younger. We discuss possible uncertainties in the observational derivation of shock front velocities due to early stripping of protostellar envelopes by ionizing radiation.     

How old are SN Ia progenitor systems? New observational constraints on the distribution of time delays from GALEX

The time delay between the formation of the progenitor systems of Type Ia supernovae (SNe Ia) and their detonation is a vital discriminant between the various progenitor scenarios that have been proposed for them. We use Sloan Digital Sky Survey optical and Galaxy Evolution Explorer ( GALEX ) ultraviolet observations of the early-type host galaxies of 21 nearby SNe Ia and quantify the presence or absence of any young stellar population to constrain the minimum time delay for each supernova. We find that early-type host galaxies lack 'prompt' SNe Ia with time delays of ≲100 Myr and that ∼70 per cent SNe Ia have minimum time delays of 275 Myr–1.25 Gyr, with a median of 650 Myr, while at least 20 per cent SNe Ia have minimum time delays of at least 1 Gyr at 95 per cent confidence and two of these four SNe Ia are likely older than 2 Gyr. The distribution of minimum time delays observed matches most closely the expectation for the single-degenerate channel with a main sequence donor. Furthermore, we do not find any evidence that subluminous SNe Ia are associated with long time delays.     

A Century of Solar Ca <Emphasis Type="SmallCaps">ii</Emphasis> Measurements and Their Implication for Solar UV Driving of Climate

Spectroheliograms and disk-integrated flux monitoring in the strong resonance line of Ca ii (K line) provide the longest record of chromospheric magnetic plages. We compare recent reductions of the Ca ii K spectroheliograms obtained since 1907 at the Kodaikanal, Mt. Wilson, and US National Solar Observatories. Certain differences between the individual plage indices appear to be caused mainly by differences in the spectral passbands used. Our main finding is that the indices show remarkably consistent behavior on the multidecadal time scales of greatest interest to global warming studies. The reconstruction of solar ultraviolet flux variation from these indices differs significantly from the 20th-century global temperature record. This difference is consistent with other findings that, although solar UV irradiance variation may affect climate through influence on precipitation and storm tracks, its significance in global temperature remains elusive.