The properties of the early-type binary Cyg OB2 #5 have been debated for many years and spectroscopic and photometric investigations yielded conflicting results. We have attempted to constrain the physical properties of the binary by collecting new optical and X-ray observations. We find that the orbital period of the system slowly changes though we are unable to discriminate between several possible explanations of this trend. The best fit solution of the continuum light curve reveals a contact configuration with the secondary star being significantly brighter and hotter on its leading side facing the primary. The mean temperature of the secondary star turns out to be only slightly lower than that of the primary, whilst the bolometric luminosity ratio is found to be 3.1. The solution of the light curve yields a distance of 925 +/- 25 pc much lower than the usually assumed distance of the Cyg OB2 association. Whilst we confirm the existence of episodes of higher X-ray fluxes, the data reveal no phase-locked modulation with the 6.6 day period of the eclipsing binary nor any clear relation between the X-ray flux and the 6.7 yr radio cycle. The bright region of the secondary star is probably heated by energy transfer in a common envelope in this contact binary system as well as by the collision with the primary's wind. The existence of a common photosphere probably also explains the odd mass-luminosity relation of the stars in this system. Most of the X-ray, non-thermal radio, and possibly gamma-ray emission of Cyg OB2 #5 is likely to arise from the interaction of the combined wind of the eclipsing binary with at least one additional star of this multiple system.
Eclipsing Binaries as Astrophysical Laboratories: Internal Structure, Convective Core Overshooting and Evolution of the B-star Components of V380 Cygni
INTEGRAL-ISGRI observations of the CygOB2 region: earching for hard X-ray point sources in a region containing several non-thermal emitting massive stars
New insights into the nature of the SMC WR/LBV binary HD 5980
本文介绍了1999年和2004- 2005年对不寻常的SMC食双星HD 5980的光波长观测结果。通过对N-IV和N-V线的可变发射线剖面进行去混合，得到了爆发的LBV/WR天体（A星）及其近距离类WR伴星（B星）的径向速度曲线，这种去混合是在简单的假设下进行的，即这些线主要来自A星和B星的风。导出的质量M_A=58- 79 Mo和M_B=51- 67 Mo，与HRD顶部附近的恒星位置比以前的估计更一致。从He I P Cygni吸收分量的轨道相位依赖行为推断风-风相互作用区域的存在。发射线强度继续下降的趋势，以前看到的紫外光谱。光球层吸收线的行为与Schweickhardt（2002）的结果一致，后者得出结论，在组合光谱中的第三个物体，恒星C，也是一个双星系统，P（starC）~96.5天，e=0.83。本文件中使用的数据将公开提供，以供进一步分析。
