摘要
本文作者对IUE数据库中5 Cet的观测资料进行处理和分析,得到它的紫外光度随轨道运动的变化,这种变化与可见光不同步,极小和极大分别出现在0.25和0.89位相.对观测资料的分析和拟合表明:5 Cet的紫外辐射来自K2Ⅲ型主星(光球和延伸大气)和吸积流打出的热斑,热斑被食是产生紫外光度变化的原因.拟合给出主星的温度为4300K,半径是23R⊙;热斑的温度为11200K,面积为2.65×10^(21)cm^2,可能位于伴星的表面.并且还得到吸积率的量级估计:M_2M≥6.2×10^(-8)M`2_⊙yr^(-1).
An archival study of 5 Cet shows that its UV flux varies over the orbital cycle in opposite direction with respect to its visual light in the sense that the minima of all UV light curves at different wavelengths occur at phase 0.25, where optical light curve reaches its maximum and UV maxima at the phase 0.89. It is inferred that a hot spot in the system is responsible for the variation. The minimum at phase 0.25 is due to the occultation of the spot which has been formed by the impingement of an outflowing stream from the giant on the surface of the companion or a disk. The inference is confirmed by the good fit to the observations. A computed continuum for the hot spot with temperature of 11200K and area of 2.65×10^(21) cm^2 (if the absolute magnitude of 5 Cet is taken to be—1.5, its distance will be 363.1 pc) fits to the difference between the observed spectra at phases 0.89 and 0.25 at level of 95 percent. If one supposes that the spot is an ellipse whose major and minor axes subtend angles of 5° and 10° at the center of the companion, it will be 3.4R_⊙ from the center. From L～GM_2 M/r～δT^4A, where A and r are the area and the distance of the hot spot from the center of the secondary, we obtained M_2M～6×10^(-8) M_⊙~2 yr^(-1). Another computed continuum for the black body with temperature of 4300K and radius of 23.2 R_⊙ fits also fairly well to the observed spectrum at phase 0.25, except the region from 1600 A to 1950A which may be attributed to the contribution of optically thin hot gas in the extensive atmosphare of a K2 giant. Therefore, the UV luminosity of 5 Cet consists of a constant component, resulting from giant primary and a variable component with the orbital motion from the hot spot. 5 Cet can reasonably be considered as a representative of a sub-type of close binaries. Therefore, the hot spot model will also be significant for these binaries. Furthermore, if the Roche-lobefilled component is a main sequence star, the visual radiation from the hot spot will distort the optical light curve, by which many asymmetric phenomena found in photometric observations may be satisfactorily explained.
出处
《天文学报》
CSCD
北大核心
1991年第3期318-325,共8页
Acta Astronomica Sinica
基金
国家自然科学基金
关键词
密近双星
紫外光度
观测
Long Period Binary—UV Luminosity of Close Binary
