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arXiv 1110.2008astro-ph.SR
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X射线耀斑的研究-- II。RS CVn型双星

A study of X-ray flares - II. RS CVn type Binaries

J. C. Pandey, K. P. Singh

摘要:

本文分析了XMM-Newton天文台观测到的5个RS CVn型双星(UZ Lib,σGem,λAnd,V711 Tau和EI Eri)的7个耀斑。这些恒星在0.3-10.0 keV能带的静态X射线光度为10^{30.7-30.9} erg/s。所有耀斑样品的指数衰减时间在~ 1 ~ 8小时之间。在0.3-10.0 keV的能量范围内,耀斑的峰值亮度在10^{30.8} - 10^{31.8} erg/s之间。XMM-EPIC仪器的高灵敏度使我们能够在耀斑期间和随后的静止阶段进行时间分辨光谱分析。在观测到的σGem、V771 Tau和EI Eri耀斑期间,日冕等离子体的金属丰度是变化的。在这些耀斑中,发现元素丰度比静止状态增加了约1.3-1.5倍。在大多数耀斑中,峰值温度超过100 MK,而排放量增加了1.5 - 5.5倍。在大多数耀斑中存在显著的持续加热。由耀斑结构导出的环长(L)为10^{10 - 11} cm量级,小于恒星半径(R*),即L/R* \lesssim 1。来自σGem的耀斑在耀斑期间表现出高的和可变的吸收柱密度。

英文摘要:

We present an analysis of seven flares detected from five RS CVn-type binaries (UZ Lib, σGem, λAnd, V711 Tau and EI Eri) observed with XMM-Newton observatory. The quiescent state X-ray luminosities in the energy band of 0.3-10.0 keV of these stars were found to be 10^{30.7-30.9} erg/s. The exponential decay time in all the sample of flares range from ~ 1 to 8 hrs. The luminosity at peak of the flares in the energy band of 0.3-10.0 keV were found to be in the range of 10^{30.8} - 10^{31.8} erg/s. The great sensitivity of the XMM-EPIC instruments allowed us to perform time resolved spectral analysis during the flares and also in the subsquent quiescent phases. The derived metal abundances of coronal plasma were found to vary during the flares observed from σGem, V771 Tau and EI Eri. In these flares elemental abundances found to be enhanced by factors of ~ 1.3-1.5 to the quiescent states. In most of the flares, the peak temperature was found to be more than 100 MK whereas emission measure increased by factors of 1.5 - 5.5. Significant sustained heating was present in the majority of flares. The loop lengths (L) derived for flaring structure were found to be of the order of 10^{10 -11} cm and are smaller than the stellar radii (R*) i.e. L/R* \lesssim 1. The flare from σGem showed a high and variable absorption column density during the flare.

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