宁静色球中HeI 10830 线的光谱特征

THE SPECTRAL CHARACTERISTICS OF HELIUM 10830 LINE IN THE UNDISTURBED CHROMOSPHERE

本文阐述用紫金山天文台太阳光谱仪新安装的雷迪康系统在1986年和1987年进行的宁静色球HeI 1083光谱观测的初步结果.得到: (1)10830线在日面边缘之外有一发射极大.1987年的发射极大强度(△I/I_(ε☉))_m比1986年明显增大. (2)极大强度(△I/I_(c☉))_m大致正比于谱线半宽. (3)冕洞区的谱线半宽明显小于非冕洞区,且与发射强度无关. (4)谱线半宽在发射极大之前基本为一常数,向外大都有变大趋势,开始变化的高度与光学厚度值有关. (5)冕洞区的光学厚度明显小于非冕洞区. (6)(△I/I_(c☉))只与黑子相对数月平滑值大体呈正变关系,而与1—8X射线流量及测点上空冕绿线的强度无相关迹象. 文中还给出我们计算的理论轮廓拟合实测轮廓的初步结果,指出难以用均匀模型很好解释所得到的观测轮廓;用一个简单的双层模型则不仅对边缘发射轮廓拟合有很大改进,而且算出的日面吸收轮廓亦较合理.因而不必象许多研究者那样非要假设一个20公里/秒的水平湍流场才能加以解释.

A number of undisturbed chromosphere spectra of Helium 10830 line were systematically obtained in 1986 and 1987 with the newly installed Reticon system at Purple Mountain Observatory. Among them, spectra of 34 limb positions taken under good seeing condition were chosen for line profile study. Preliminary analysis shows the following results: (1) Each emission curve shows a maximum beyond the solar limb. The mean value of the maxima is obviously larger in 1987 than in 1986, implying that even in the undisturbed chromosphere, the HeI emission has an evident long-term variation which might relate to the solar cycle. (2) The maximum intensities, (ΔI/I_(c⊙))_m of different measured positions are approximately directly proportional to their half-widths Δλ_((1/2)(R)). (3) The half-widths of the lines in coronal holes are systematically smaller than those outside, and no correspondence with the emission intensity has been found. (4) The line half-width almost keeps constant before the emission curve reaches maximum. But in most cases, the line tends to be wider as height increases. Meanwhile it is interesting to note that the height where half-width begins to increase seems to depend on the optical depth of the line. (5) The optical depth are obviously smaller in the coronal holes than outside. (6) Except that the (ΔI/I_(c⊙))_m increases roughly with the monthly sunspot number, we have failed to see any correspondence between (ΔI/I_(c⊙))_m and the 1—8 X-ray flux, and the intensity of the green coronal line above the sites measured as well. Also presented in the final section, is some discussions on the methods for deriving parameters from the observational line profiles. First we tried a uniform chromosphere model, but found that most of the observational HeI 10830 line profiles can hardly be fit well to the calculated ones. Next, a two-layer chromosphere model was derived, each layer having constant parameters and the Doppler width in the outer layer being 1.5 times larger than that in the inner. Consequently, not only wab the fit between the observational line profiles and the theoritical ones greatly improved, the absorption line profiles on the disk calculated with the same set of parameters obtained also seem rather reasonable for line depths and half-widths. Therefore, the assumption of a non-isotropic turbulence fields is no longer needed for explaining the 10830 line profiles in the chromosphere spectra.