Semiregular variables in the solar neighbourhood     

I. S. Glass  F. van Leeuwen 《Monthly notices of the Royal Astronomical Society》2007,378(4):1543-1549

Period–luminosity sequences have been shown to exist among the semiregular variables (SRVs) in the Magellanic Clouds, the bulge of the Milky Way galaxy and elsewhere. Using modern-period and revised Hipparcos parallax data, this paper demonstrates that they also appear among the M giant SRVs of the solar neighbourhood. Their distribution in the   K , log  P   diagram resembles that of Bulge stars more closely than those in the Magellanic Clouds. The prevalence of mass-loss among local M-type SRVs and its dependence on period and spectral subtype are also discussed.   K −[12]  , a measure of circumstellar dust emission, increases clearly with V amplitude, M giant subtype and  log  P   .  相似文献   

Gamma-ray burst precursors as the remnant of the thermal radiation initially trapped in the fireball     

Li-Xin Li 《Monthly notices of the Royal Astronomical Society》2007,380(2):621-636

In the standard fireball model of gamma-ray bursts (GRBs), the fireball starts with an optically thick phase. As it expands, the fireball becomes optically thin at some stage. The thermal radiation trapped in the originally opaque fireball then leaks out, producing a transient event. The appearance of the event is investigated in the framework of a homogeneous, spherically symmetric and freely expanding fireball produced instantly by an explosive process without continuous injection of mass and energy. We find that, generally, the event has a time duration shorter than that of the main burst, which is presumably produced by the internal shock after the fireball becomes optically thin. The event is separated from the main burst by a quiescent time interval, and is weaker than the main burst at least in a high-energy band. Hence, the event corresponds to a GRB precursor. The precursor event predicted by our model has a smooth and Fast Rise and Exponential Decay (FRED) shaped light curve, and a quasi-thermal spectrum. Typically, the characteristic blackbody photon energy is in the X-ray band. However, if the distortion of the blackbody spectrum by electron scattering is considered, the characteristic photon energy could be boosted to the gamma-ray band. Our model may explain a class of observed GRB precursors – those having smooth and FRED-shaped light curves and quasi-thermal spectra.  相似文献   

Reionization scenarios and the temperature of the intergalactic medium     

Eric R. Tittley  Avery Meiksin 《Monthly notices of the Royal Astronomical Society》2007,380(4):1369-1386

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Absolute diffuse calibration of IRAC through mid-infrared and radio study of H ii regions     

Martin Cohen  Anne J. Green  Marilyn R. Meade  Brian Babler  Rémy Indebetouw  Barbara A. Whitney  Christer Watson  Mark Wolfire  Mike J. Wolff  John S. Mathis  Edward B. Churchwell 《Monthly notices of the Royal Astronomical Society》2007,374(3):979-998

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一种基于滨海核电站海上γ辐射剂量率的智能化自动监测系统研究与设计          下载免费PDF全文

刘占阳  胡澄  孙雪峰  张启明  陈谦  杨立涛  贺一凡 《应用海洋学学报》2020,39(2):273-278

基于滨海核电站海上γ辐射剂量率的智能化自动监测系统是一种无人值守的辐射监测装备,可全天候、长时间、在线组网、连续自动测量水面和空气中的γ剂量率、获取水中γ能谱数据并进行核素识别和计算活度浓度,并实时地将监测数据通过无线通信链路和北斗短报文两种形式上传至地面数据服务中心。在非事故情况下,该系统是对核电厂监督性监测系统的重要补充和完善;在发生重大核安全事故或放射性物质泄漏的情况下,能够有效解决传统的派船巡测时方法不标准、数据不及时不连续、人员受照风险大、船只易受污染和行动代价高等问题;在恶劣的极端气象条件下,无人值守的自动监测系统能够为核电站提供实时有效的水体和空气中的γ剂量率、气象、海水温度等监测数据,有效地提升了核电站在极端气象条件下的监测能力,对滨海核电站整体的安全性和可靠性具有一定积极意义。  相似文献   

Particle decay in the early Universe: predictions for 21 cm     

Yu. A. Shchekinov  E. O. Vasiliev 《Monthly notices of the Royal Astronomical Society》2007,379(3):1003-1010

The influence of ultra-high energy cosmic rays (UHECRs) and decaying dark matter particles on the emission and absorption characteristics of neutral hydrogen in 21 cm at redshifts   z = 10–50  is considered. In the presence of UHECRs, 21 cm can be seen in absorption with the brightness temperature   T _b=−(5–10) mK  in the range   z = 10–30  . Decaying particles can stimulate a 21-cm signal in emission with   T _b∼ 50–60 mK  at   z = 50  and   T _b≃ 10 mK  at   z ∼ 20  . Characteristics of the fluctuations of the brightness temperature, in particular its power spectrum, are also calculated. The maps of the power spectrum of the brightness temperature on the plane wavenumber redshift are shown to be sensitive to the parameters of UHECRs and decaying dark matter. Observational possibilities to detect manifestations of UHECRs and/or decaying particles in 21 cm with the future radio telescopes (LOFAR, 21CMA and SKA), and to distinguish contributions from them, are briefly discussed.  相似文献   

Can the early X-ray afterglow of gamma-ray bursts be explained by a contribution from the reverse shock?     

F. Genet  F. Daigne  R. Mochkovitch 《Monthly notices of the Royal Astronomical Society》2007,381(2):732-740

We propose to explain the recent observations of gamma-ray burst early X-ray afterglows with SWIFT by the dissipation of energy in the reverse shock that crosses the ejecta as it is decelerated by the burst environment. We compute the evolution of the dissipated power and discuss the possibility that a fraction of it can be radiated in the X-ray range. We show that this reverse shock contribution behaves in a way very similar to the observed X-ray afterglows if the following two conditions are satisfied. (i) The Lorentz factor of the material which is ejected during the late stages of source activity decreases to small values  Γ < 10  and (ii) a large part of the shock-dissipated energy is transferred to a small fraction  (ζ≲ 10⁻²)  of the electron population. We also discuss how our results may help to solve some puzzling problems raised by multiwavelength early afterglow observations such as the presence of chromatic breaks.  相似文献   

The morphology of H ii regions during reionization     

Matthew McQuinn  Adam Lidz  Oliver Zahn  Suvendra Dutta  Lars Hernquist  Matias Zaldarriaga 《Monthly notices of the Royal Astronomical Society》2007,377(3):1043-1063

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The vertical attenuation of irradiance as a function of turbidity: a case of the Huanghai(Yellow) Sea in spring   总被引：1，自引：0，他引：1  

LINShaoying  ZOUTao  GAOHuiwang  GUOXinyu 《海洋学报(英文版)》2009,28(5):66-75

The planar photosynthetically available radiation (PAR), turbidity and concentration of chlorophyll a (chl a), were measured at 26 stations in the Huanghai (Yellow) Sea during a cruise of China SOLAS from 19 to 27 March 2005. Due to low chl a (<0.35 mg · m-3 ) in upper layers (above 5 m), suspended particulate matter became the major factor that influenced the turbidity in early spring. The calculated vertical diffuse attenuation coefficient of PAR, K PAR , varied with water depths with a maximum value in t...  相似文献   

2006～2007年北部湾海-气热通量变化特征     

盛立芳  郑元鑫  陈静静  王丹 《中国海洋大学学报(自然科学版)》2009,39(4)

用2006年夏～2007年秋在北部湾获得的船测气象资料,由块体公式计算了海-气通量.结果表明:北部湾春、夏季节获得热通量,而秋、冬季节失去热通量.春季通过湍流交换造成的热通量对海面热平衡的贡献最小,其次是夏季、冬季和秋季.在年平均尺度上感热通量和潜热通量分别占净辐射通量的7.4%和77.4%,15.2%的净辐射热量通过海洋过程消耗掉.感热通量随海-气温差的加大而增大,而与风速之间呈现复杂的非线性关系.海-气温差增加1 ℃,感热通量增加6.7～12.7 W/m2;较大的感热通量(>30 W/m2)容易出现在5～10 m/s风速条件下.潜热通量与风速和相对湿度呈明显的相关关系:风速增加1 m/s,潜热通量增加约18 W/m2,而相对湿度下降1%会导致6 W/m2潜热通量的增加.  相似文献