Algol型雙星的觀測研究

張嘉

(中國科學院云南天文臺昆明650011)

Algol型雙星的觀測研究

張嘉?

(中國科學院云南天文臺昆明650011)

Algol型雙星是雙星的一種,其獨特的半接結構使它擁有豐富的物理現象,包括嚴重畸變的充滿子星、強磁活動現象,物質轉移的各種形式,完全迥異于單星的演化狀態(tài)和特有的形成歷史.本文對雙星光變曲線的基礎物理做了介紹,同時介紹了歷史上的各個模型或程序.展示了各個物理參數對光變曲線的影響,包括傾角、溫度、金屬豐度、表面重力加速度、第3光、半徑、軌道橢率和軌道近點角等.根據已有星表統(tǒng)計了Algol型雙星的性質,并對3顆樣本星進行了具體的觀測和分析,結果如下:

(1)對Algol型雙星進行了統(tǒng)計分析,結果支持前人的分離子星大多為主序星的結論.質量比的分布支持我們對于Algol型雙星質量比臨界值的理論計算,同時猜測Algol型雙星的半徑比可能存在下限.發(fā)現Algol型雙星中兩子星的溫度、光度、半徑和質量等都具有較好的相關性.

(2)觀測并分析了雙星FG Gem.基于不同溫度、光度組合的大量的解軌參數,使用新的對比年齡的方法得出雙星FG Gem是半接雙星的結論.使用新的溫度搜尋的方法改善了對分離子星溫度的估計值.對FG Gem特殊的周期變化,提出原因可能是間斷性物質流和持續(xù)的磁滯的共同作用.

(3)以雙星VV Vir為例,討論了Algol型雙星中物質流的一些性質.某些性質可以反映半接系統(tǒng)中物質流的一些共性,包括:流的半徑很小,進而造成的撞擊斑的半徑也很小.在物質轉移率較高的情況下,物質流的能量轉移率可以比擬分離子星的本征光度.撞擊斑的位置由周期、質量比和分離子星的無量綱勢決定.撞擊斑的溫度很高,并能夠以駝峰的形式直接反映在光變曲線上.

(4)發(fā)現了1顆罕見的正處在質量比反轉過程中的Algol型雙星V753 Mon,這顆雙星的質量比非常接近1,處在雙星演化的關鍵階段,為雙星演化理論提供了觀測標本.

(5)介紹了光變曲線模型及其各個物理因素,包括軌道的形狀、恒星的形狀、引力致亮效應、恒星大氣模型、臨邊昏暗效應、反射效應、掩食效應、第3天體及第3光、黑子和磁效應、熱斑、恒星震動、大氣掩食和星周物質等.梳理并介紹了歷史上的各個光變曲線分析程序.對光變曲線的參數逐一進行了分析和結果展示,包括軌道傾角、恒星表面溫度、表面金屬豐度、表面重力加速度、第3光、恒星半徑(由表面勢表述)、雙星軌道橢率和近點角等.

The Algol-Type binary systems are a subtype of binary systems.Their unique semidetached structure leads to have abundant physical phenomena,including the dramatically distorted donor star,strong magnetic activities,various ways of mass transfer,the evolution stage quite di ff erent from that of single stars,and speci fi c formation tracks.In this paper,we introduce the fundamental physics of light curves,as well as the models or programs used in the past.We show the in fl uence of di ff erent parameters on the light curves,including the inclination,temperature,abundance,surface gravity,the third light,radius,orbital eccentricity,and the argument of periastron.Based on the current catalog of Algols,we investigate their statistic characteristics.We observe three Algols and analyze the data in detail.The results are as follows:

(1)Our statistical analyses of Algols support the previous suggestion that most of the detached component stars are main sequence stars.The distribution of the mass ratio agrees to our calculated critical value of the mass ratio for Algols.We suggest that there could be a lower limit of the radius ratio.We also show that there are good correlations among the temperature,luminosity,radius,and the mass of the component stars.

(2)The binary FG Gem is observed,and the data are analyzed.Based on the solutions of large combinations of the temperature and luminosity,we use a new age-comparing method to show that the FG Gem is a semi-detached system,and a new temperaturesearching method to get a better estimate of the temperature of the detached component star.We suggest that a combination of the intermittent mass fl ow and the continuous magnetic braking can explain its orbital period change.

(3)Taking the VV Vir as an example,we discuss some properties of the mass fl ow in a semi-detached binary.Some of them can re fl ect the common characteristics of the mass fl ows in the Algol systems,e.g.,the radius of the mass fl ow is very small,so is its impact spot.If the mass transfer rate is high,the energy transfer rate can be comparable to the intrinsic luminosity of the detached component star.The position of the impact spot can be determined by the orbital period,mass ratio,and the dimensionless potential.The temperature of the impact spot is very high,and it can be directly re fl ected by the humps on the light curves.

(4)We discover a rare Algol binary V753 Mon,which is just in the process of mass ratio inversion.The mass ratio of this binary is very close to one,and the key evolutional stage provides an important observational source for the theoretical studies of binary evolution.

(5)We introduce the light curve models and the related physical factors,including the shape of the orbit,the shape of the stars,gravity brightening,atmosphere model,limb darkening,re fl ection e ff ect,eclipse e ff ect,the third body and its third light,dark spots and magnetic e ff ect,hot spots,asteroseismology,atmospheric eclipse,and circumstellar matter. The light curve analysis programs are presented.We analyze the parameters and show the relevant results,including the orbital inclination,surface temperature,metal abundance, gravity acceleration,the third light,stellar radius(expressed by the surface potential),the eccentricity of the orbit,and anomaly.

An Observational Study of Algol-Type Binary System

ZHANG Jia
(Yunnan Observatories,Chinese Academy of Sciences,Kunming 650011)

10.15940/j.cnki.0001-5245.2015.01.011

?2014-01-05獲得博士學位,導師:云南天文臺錢聲幫研究員;zhangjia@ynao.ac.cn